Isolation of two trypsin-like proteases associated with the outer membranes of Bacteroides gingivalis By HELEN G. SCOTT D.D.S., University of Alberta, 1976 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE In THE FACULTY OF GRADUATE STUDIES THE FACULTY OF DENTISTRY DEPARTMENT OF CLINICAL DENTAL SCIENCES We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November 1988 © Helen G. Scott, 1988 In presenting degree freely at this the available copying of department publication of in partial fulfilment University of British Columbia, for this or thesis reference thesis by this for his and scholarly or thesis study. her for of gain shall permission. Department of n i n i r a l The University of British 1956 Main Mall Vancouver, Canada V6T 1Y3 Date DE-6(3/81) September 2, n p n f a l Columbia 1988 S r i p n p P R that agree may representatives. financial requirements I agree I further purposes the be It not is that the Library permission granted by understood be for allowed an advanced shall for the that without make it extensive head of my copying or my written ABSTRACT Two proteases, P-1 and P-4, present in the outer membranes of gingivalis Bacteroides A T C C 33277, were isolated and partially purified by S D S - P A G E . The purification procedures resulted in a specific activity 45-fold (P-1) and 40-fold (P-4) greater than that of the crude fractions. of proteolytically active P-1 produced three bands Electrophoresis corresponding to molecular weights of 235, 220 and 200 kD whereas electrophoresis of proteolytically active P-4 produced one major band corresponding to 74 kD. The optimum temperature and pH for activity were determined using N-5benzoyl-D-arginine-p-nitroanilide as substrate. The proteases were most active at 37 °C and at pH values between 6.0 and 6.5. Both proteases required a reducing agent for activity and were inhibited by a variety of serine and thiol protease inhibitors. Arginine-containing peptides were readily hydrolyzed whereas the proteases were less active against glycine-containing peptides. The proteases hydrolyzed IgA, IgG, gelatin, azocoll and azoalbumin; acid-soluble collagen was not degraded. The results of this investigation suggest that these are trypsin-like proteases which have a thiol component as part of the active site. ii TABLE OF CONTENTS Abstract ii List of tables v List of figures vi Acknowledgements vii Introduction 1 Classification of black-pigmented Bacteroides 1 Antigenic and serologic characteristics of B. gingivalis 3 Ultrastructural studies 3 Ecology of Bacteroides gingivalis 4 Growth and nutrition 4 Metabolic end-products of Bacteroides gingivalis 7 Formation and characterization of vesicles 7 Adherence properties of Bacteroides gingivalis 8 Fimbriae 9 Surface-binding proteins 9 Hemagglutination properties 10 Experimental infections involving B P B s 11 Periodontal diseases 12 Virulence factors of Bacteroides gingivalis 14 Adherence properties 14 Capsule 15 Outer membrane vesicles 16 Lipopolysaccharide 17 Metabolic end-products 17 Enzyme activities 18 Types of proteases 21 Proteases of Bacteroides gingivalis 22 Protelytic activity of other pathogenic organisms Aim of the investigation 27 29 iii Material and methods Bacterial strain and culture conditions Isolation and purification of proteases Preparation of outer membranes Preparative polyacrylamide gel electrophoresis Protein determination Protein profiles of OM-1 and OM-2 Protein profiles of P-1 and P-4 Proteolytic activity of OM-1, OM-2, P-1, P-4 Peptidase activity Optimum pH Optimum temperature and heat stability Inhibition of protease activity Hydrolysis of protein substrates Immunoreactivity Chemicals Results Purification Peptidase activity Optimum pH Optimum temperature and heat stability Inhibition of enzyme activity Activity against protein substrates Immunoreactivity Discussion Bibliography iv LIST OF TABLES TABLE PAGE 1 Purification of 2 Peptidase activity of P-1 and P-4 52 3 Effect of protease inhibitors and metal ions 59 4 Activity against protein substrates 60 v P-1 and P-4 47 LIST OF FIGURES FIGURE > PAGE 1 S D S - P A G E of outer membranes-1 43 2 S D S - P A G E of outer membranes-2 44 3 Zymogram of proteases after preparative S D S - P A G E 45 4 S D S - P A G E of P-1 49 5 S D S - P A G E of P-4 50 6 S D S - P A G E showing proteolytic purity of OM-2, P-1, P-4 51 7 Optimum pH for the hydrolysis of BAPNA by P-1 55 8 Optimum pH for the hydrolysis of BAPNA by P-4 56 9 Optimum temperature for the hydrolysis of BAPNA 57 10 Heat stability of P-4 58 1 1 Hydrolysis of IgA and IgG by P-1 and P-4 62 12 Hydrolysis of gelatin and collagen by P-1 and P-4 63 13 Hydrolysis of collagen by trypsin and P-1 64 vi I ACKNOWLEDGEMENTS I am deeply grateful to Dr. B. C. McBride for his understanding and guidance, and for his continued support and encouragement of this project, and for the financial support of the University of British Columbia. My sincere thanks to Drs. John Silver and Jukka Uitto for serving on my committee and for their guidance and support, and I gratefully acknowledge the constant encouragement of the members of the Division of Periodontics. I wish to give special thanks to Dr. Daniel Grenier who so generously shared his knowledge and experience with me, and who was always a source of encouragement. I give my sincere thanks to Meja Song, Heather Merilees and Pauline Hannam who asssisted me by sharing their technical skills and experience, and for their constant support and encouragement. I extend to my fellow students, Angela Joe, Nadarajah Ganeshkumar, Umadatt Singh and Blair Heffelfinger, my sincere gratitude for consistently sharing their experience and knowledge, and for their fellowship and humour. I also wish to thank Bruce McCaughey and Harold Traeger for their photography in the preparation of this work. I take this opportunity to express my gratitude to my family and friends their unfailing support and confidence. vii for INTRODUCTION Bacteroides findings gingivalis is c o n s i d e r e d to be a periodontal pathogen b a s e d upon the of n u m e r o u s investigations which have identified this o r g a n i s m in association with a variety of periodontal d i s e a s e s (reviewed by v a n Winkelhoff et al, 1988). Furthermore, B. gingivalis p o s s e s s e s a number of virulence factors which may be potentially d a m a g i n g to the periodontal t i s s u e s . T h e periodontal pocket p r o v i d e s an e c o l o g i c a l environment w h i c h is ideal for c o l o n i z a t i o n by these organisms. Classification of black-pigmented Black-pigmented Bacteroides Bacteroides ( B P B ) are G r a m - n e g a t i v e , obligately anaerobic, non-motile, n o n s p o r e f o r m i n g , r o d - s h a p e d o r g a n i s m s which p r o d u c e b r o w n to black c o l o n i e s o n solid m e d i a containing blood. T h i s group of m i c r o - o r g a n i s m s w a s first d e s c r i b e d by O l i v e r a n d W h e r r y (1921) w h o n a m e d the Bacterium b e c a u s e they b e l i e v e d the dark pigment to be melaninogenicum melanin. T h e s e bacteria were later a s s i g n e d to the genus Bacteroides Bacteroides and Courant and named (Roy and Kelly, 1939). melaninogenicus T h i s w a s the only B P B s p e c i e s r e c o g n i z e d until 1970, (1962) and Gibbons (1967) had although S a w y e r et al shown biochemical i m m u n o l o g i c a l heterogeneity a m o n g strains of B. melaninogenicus. and M o o r e (1970) divided B. melaninogenicus their f e r m e n t a t i v e (strongly abilities: fermentative), fermentative) and B. organism B. B. subsp. melaninogenicus s u b s p . intermedius subsp. melaninogenicus Holdeman into three s u b s p e c i e s b a s e d upon melaninogenicus melaninogenicus and (weakly (non- asaccharolyticus fermentative). Sufficient biochemical and genetic differences were found between saccharolytic and asaccharolytic s u b s p e c i e s to elevate B. melaninogenicus asaccharolyticus to the s p e c i e s level ([B. 1 asaccharolyticus], the subsp. Finegold and B a r n e s , 1977). Further research (Coykendall et al, 1980; v a n S t e e n b e r g e n et al, 1979) indicated that the D N A of asaccharolytic B P B strains isolated from the h u m a n oral cavity c o n t a i n e d b e t w e e n 4 7 a n d 4 9 mol% g u a n i n e plus cytosine (G+C) w h e r e a s the D N A isolated from non-oral strains contained between 52 a n d 53 mol% (G+C). Furthermore, no D N A homology w a s found between the D N A s of the oral a n d the non-oral strains. asaccharolytic species, It w a s therefore p r o p o s e d , that a s e c o n d Bacteroides be recognized gingivalis, designate oral strains (Coykendall et al, 1980; which would v a n S t e e n b e r g e n et al, 1982). A n e w s p e c i e s of asaccharolytic Bacteroides, which c a n b e d i s t i n g u i s h e d B. a n d from B. gingivalis S t e e n b e r g e n et al (1984): asaccharolyticus, Bacteroides has been endodontalis. proposed from by v a n This proposal c a m e after the evaluation of the two asaccharolytic B P B strains by V a n S t e e n b e r g e n et al, (1982). T h e s e two strains were originally isolated by Sundqvist ( G . Sundqvist, P h . D. thesis, University of U m e a , U m e a , S w e d e n , 1976, a s reviewed by M a y r a n d & Holt, 1988). B. endodontalis c a n be differentiated from the other asaccharolytic s p e c i e s by its lower G + C content a n d by the a b s e n c e of antigens c o m m o n to other a s a c c h a r o l y t i c B P B s . identified by their differing polyacrylamide endodontalis Furthermore, all three s p e c i e s c a n b e protein profiles gel electrophoresis following s o d i u m d o d e c y l (van S t e e n b e r g e n sulfate- et a l , 1 9 8 4 ) . B. h a s b e e n isolated from mixed oral infections, predominantly from p y o g e n i c infections of odontogenic origin (van Winkelhoff et al, 1985) a n d from root c a n a l infections ( H a a p a s a l o et al, 1986). Bacteroides gingivalis periodontal p o c k e t is isolated primarily from the h u m a n gingival s u l c u s or a n d differs from the non-oral B. asaccharolyticus production of p h e n y l a c e t i c acid ( K a c z m a r e k a n d C o y k e n d a l l , 1 9 8 0 ; 1979), by Mayrand, hemagglutination of s h e e p erythrocytes (Slots a n d G e n c o , 1979), by a trypsin-like e n z y m e activity (Slots, 1981), a n d by serology 1978; by the M o u t o n et a l , 1981). 2 ( M a n s h e i m et al, Antigenic and serologic characteristics of Bacteroides gingivalis Reed et al (1980) demonstrated the antigenic specificity of B. and B. gingivalis asaccharolyticus using Immunoelectrophoresis and immunodiffusion techniques. The results of their work showed that none of the strains from non-oral sites was antigenically similar to B. gingivalis and furthermore, no common antigens were found between the asaccharolytic and saccharolytic BPB strains. Parent et al (1986) observed that B. gingivalis consisted of at least two serogroups, and found that the human biotype exhibited 25 surface antigens, two of which were specific for the biotype. serogroups of B. gingivalis Fisher et al also demonstrated two (J.G. Fisher, J.J. Zambon, P. Chen and R.J. Genco, J . Dent. Res. 65:816, abstr. 817, 1986) and found that these groups were associated with the virulence of the strain. major protein band at 54 kD which was The virulent strains produced a absent in the avirulent strains. Furthermore the electrophoretic profile produced by cell envelope proteins of virulent and avirulent strains differed (Bramanti and Holt, J . Dent. Res. 66:223, abstr. 930, 1987), and this difference was apparently represented in the pathogenicity of the organism. Ultrastructural studies Electron microscopy observations (Takazoe et al, 1971) revealed the presence of an external capsule and fimbria-like structures in a pathogenic strain of gingivalis. B. The electron microscopy studies of Mansheim and Kasper (1977), revealed a typical Gram-negative morphology: the cells had an inner and outer cell membrane separated by a thin peptidoglycan layer. Furthermore, the oral strain, but not the non-oral strain, was found to have capsular material external to, and associated with, the outer membrane. A recent electron microscopic survey by Handley and Tipler (1986) also revealed the presence of fimbriae and of a layer of material external to the outer membrane. In addition, B. gingivalis produces outer membrane vesicles (blebs) which are 3 formed by pinching or budding of the outer membrane (Grenier 1987; Listgarten and Lai, 1979; Woo et al, 1979). and Mayrand, The number of vesicles released may be related to growth conditions (McKee et al, 1986). The vesicles have been shown to be proteolytic and collagenolytic, to hemagglutinate erythrocytes and to mediate attachment between noncoaggregating bacterial species (Grenier and Mayrand, 1987). of Bacteroides Ecology Bacteroides pocket gingivalis gingivalis colonizes the human gingival sulcus and periodontal (Slots and Genco, 1979) and has occasionally been isolated from oral mucosal surfaces (van Winkelhoff, 1986b; Zambon et al, 1981). The organism is usually absent from a healthy gingival sulcus, however, it may constitute <15% of the cultivable subgingival flora from individuals with gingivitis (Slots, 1982; Slots et al, 1978; White and Mayrand, 1981; Zambon et al, 1981), and the proportion of B. gingivalis increases significantly periodontitis (Loesche et al 1985; Slots, 1977b; al, 1979; White and Mayrand, 1981). in cases of adult Spiegel et al, 1979; Tanner et In addition, this organism is routinely found in those sites which are deemed to be actively progressing (Slots et al, 1986; Growth Tanner et al 1984). and nutrition Morphologically, B P B are uniform or pleomorphic rods; cells in broth culture are coccobacillary, 0.5 urn wide by 1-2 urn long. Growth on blood agar produces colonies which are 1-2 mm in diameter, convex, and form black pigment in 710 days. This black pigmentation, originally thought to be melanin by Oliver and Wherry (1921), was found by Shah et al (1979) to be protohemin, a watersoluble, intracellular or cell-associated derivative of hemoglobin (Duerdan, 1975). Bacteroides gingivalis will grow on solid medium or in broth culture containing small peptides plus hemin and vitamin K as growth factors (Gibbons and MacDonald, 1960; Wahren and Gibbons, 1970). 4 Vitamin K can be replaced by menadione (Gibbons and MacDonald, 1960), and succinate can take the place of hemin as a growth factor (Mayrand and McBride, 1980). proposed a selective medium for B. gingivalis Hunt et al (1986) {Bacteroides gingivalis agar, BGA) containing bacitracin, colistin and nalidixic acid as the selective agents. They found that this medium could be used to differentiate between B. and B. asaccharolyticus and could isolate B. gingivalis gingivalis from other oral bacteria. Colistin and nalidixic acid inhibit aerobic and facultatively anaerobic, Gramnegative bacteria, and bacitracin inhibits Gram-positive bacteria and is active against many other oral species. Seddon et al (1988) described chemically defined and minimal media for the growth of Bacteroides gingivalis. The chemically defined medium contained only twelve components and was able to support the growth of cells in culture which were morphologically identical to those grown in other media. metabolic end-products Furthermore, the of cells grown in this medium were reproducible and yielded patterns similar to those produced in complex media. The growth rates were approximately 50% slower than those of cells grown in a complex medium, however, when the defined medium was supplemented with protein hydrolysates, the rate of cell growth was increased. The effect B. gingivalis of hemin concentration upon the physiology strain W50 was studied by McKee et al (1986). and virulence of They found that no growth occurred in the absence of hemin, although a complex proteinaceous medium supplemented with vitamin was used. Cells grown under conditions of hemin limitation produced few fimbriae, but large numbers of extracellular vesicles were observed surrounding the cells and free within the medium. Conversely, under conditions of hemin excess, the cells were heavily fimbriated and few vesicles were noted. Furthermore, cells grown in medium lacking hemin were avirulent when injected into mice whereas the injection of cells grown in medium supplemented with hemin produced up to 50% mortality in mice. conclusion was that Their the hemin concentration of the medium modulated not only 5 cell growth, but also the virulence of the organism. Based upon this apparently obligate requirement for hemin, it is not surprising that B. gingivalis is highly effective in degrading heme-containing plasma proteins (Carlsson et al, 1984) or that there is a proportionate increase in the number of Bacteroides species when bleeding develops as a result of disease progression (Loesche and Syed, 1978). Shah and Williams (1987) found that B. gingivalis grew best in medium in which glucose was absent, and if glucose was present, little was metabolized (3%). Prolific growth was produced in medium containing protein hydrolysates. Nutritional relationships can exist between certain bacteria the result of which is an enhancement of growth for one or both organisms. For example, BPB species exhibit enhanced growth in the presence of naphthoquinone, a vitamin Krelated compound (MacDonald et al, 1963) and the hemin required by gingivalis B. can be replaced by the succinate produced by facultative organisms which ferment glucose (Mayrand & McBride, 1980) or by capnophilic bacteria (Grenier & Mayrand, 1985). More recently, Grenier & Mayrand (1986) found that protoheme, produced by W. recta in coculture with B. gingivalis, the growth of this Bacteroides gingivalis species. enhanced Furthermore, once established, B. can promote its own growth by suppression of other bacterial species by the production of hematin or bacteriocin (Takazoe et al, 1984). The growth of a pathogenic strain of B. gingivalis (W50) under conditions of varying pH was examined by McDermid et al (1988). Using chemostat conditions, stable growth occurred over the pH range 6.7 to 8.3, but could not be maintained at pH 6.5 or pH 8.5. A maximum yield of cells was obtained when the cultures were maintained between pH values of 7.0 and 8.0. The enzymatic activity of the cells was also found to vary according to the growth pH. Trypsin- like activity increased with the growth pH and was maximal at pH 8.0, whereas the specific enzyme activity of collagenase and hyaluronidase was greatest at, or below a neutral growth pH. 6 Metabolic end-products of Bacteroides gingivalis Some products resulting from the metabolism of nutrients by B. gingivalis are considered to be virulence factors of the organism (van Steenbergen et al, 1982). These include organic acids: isovaleric (Lambe et al, 1982; acetic, proprionic, butyric, isobutyric, Reed et al, 1980; Shah et al, 1976) which are produced in common with other Bacteroides is produced only by B. gingivalis species. However, phenylacetic acid (Kaczmarek and Coykendall, 1980; Mayrand, 1979) and was found to be directly proportional to the Trypticase content of the medium; L-phenylalanine and peptides containing this amino acid also enhanced the production of phenylacetic acid (Bourgeau and Mayrand, 1983). Ammonia and indole (MacDonald and Gibbons, 1962; van Steenbergen et al, 1986b) and volatile sulphur compounds, including hydrogen sulphide, dimethyl sulphide and methylmercaptan (Tonzetich and McBride, 1981) are produced by B. gingivalis and are considered to be virulence factors detrimental to the host. The large quantities of ammonia produced (Shah et al, 1987) contribute to the rise in pH during growth of B. gingivalis in broth culture (McDermid, 1988) and may have a similar effect within the periodontal pocket where the pH has been shown to increase with an increase in pocket depth and with the severity of the host inflammatory response (Bickel and Cimasoni, 1985). Formation and characterization of extracellular vesicles The formation of extracellular vesicles by B. gingivalis has been reported by Williams and Holt (1985) and by McKee et al (1986). Williams and Holt (1985) recovered outer membrane fragments (vesicles) by ultracentrifugation of culture supernatant. They found that although there was a distribution of sizes, vesicles of approximately 50 nm predominated. The polypeptide profile of the vesicles was similar, but not identical, to that of the outer membranes, as analyzed by S D S - P A G E . There were at least two polypeptide bands, at 16 and 18 kD, found in the outer membrane fraction of B. gingivalis detectable in the vesicle fraction. which were not In addition, there were minor differences 7 between the fractions in the intensity of the protein staining of some of the bands. Grenier and Mayrand (1987) characterized some of the biological activities of extracellular vesicles isolated from B. gingivalis. They, too, found a variation in vesicle size from 20-150 nm, but a predominance of vesicles of 50 nm diameter. However, in contrast to the study of Williams and Holt (1985), Grenier and Mayrand (1987) found two supplementary polypeptide bands between 45 and 66 kD in the vesicle fraction which were not apparent in the polypeptide profile of the outer membranes. This difference between the two studies could be the result of having used two different strains of B. for comparison of the polypeptide patterns; gingivalis gingivalis Williams and Holt (1985) used B. strain W whereas Grenier and Mayrand (1987) used a nonpathogenic strain, A T C C 33277. The vesicles were found to be both proteolytic and collagenolytic and were able to agglutinate sheep erythrocytes, activities which are identical with those of the whole cell. Furthermore, the vesicles mediated coaggregation between bacterial cells of two species, Eubacterium and Capnocytophaga ochracea, saburreum by forming a physical link or bridge between the cells, as seen by electron microscopy. This coaggregation was stable over a pH range from 4.5 to 8.5 (Grenier & Mayrand, 1987). Adherence properties of Bacteroides gingivalis A primary requirement of an organism, in order to colonize and grow within a host, is an ability to attach to host surfaces. Specific adhesins on the surface of bacterial cells are responsible for the attachment to specific host receptors (Holt, 1982). The adhesins on the cell surface of Gram-negative bacteria include type-specific pili or fimbriae, hemagglutinins and other surface-binding proteins (Ofek and Perry, 1985). colonize the dentition at discrete sites. It is characteristic of B. gingivalis to Attachment potential, host and bacterial interactions, nutritional, physical and chemical factors are determinants which will affect the colonization pattern. 8 1. Fimbriae Fimbriae from B. gingivalis Yoshimura et al, (1984) and that the fimbriae from B. have been isolated, purified and characterized by Yoshimura et al, (1985). are gingivalis thin, curly, approximately 5 nm long and with a diameter of 4 nm. Their studies indicate heat-stable filaments The component subunit, fimbrillin, has an apparent molecular weight of 43 kD and a primary structure different from that of other Gram-negative bacteria (Yoshimura et al, 1985). Furthermore, native fimbriae and denatured fimbrillin have differing immunological characteristics and show little cross-reactivity. Work done by Okuda & Takazoe (1974) seemed to indicate that the fimbriae conferred hemagglutinating (HA) activity, however, a pure preparation of fimbriae (Yoshimura et al, 1984) showed neither HA activity, nor inhibition of HA activity. Slots and Gibbons (1978) reported that B. gingivalis was able to attach to both buccal and crevicular epithelial cells, and to the surfaces of Grampositive bacteria. However, the attachment of B. gingivalis to epithelial cells and to erythrocytes was inhibited by both saliva and serum. These fluids did not inhibit the attachment to Gram-positive bacteria. What this suggests is that there may be two types of adhesins on the surface of B. gingivalis. This hypothesis is supported by the fact that both those strains which have HA activity, and those which do not, exhibit fimbriae on their cell surface. Furthermore, heating for 15 minutes at 60 ° C abolished the HA activity of a partially purified preparation of fimbriae (Slots and Gibbons, 1978). 2. Surface-binding properties The ability to bind to specific host proteins may assist the organism in colonization, in protection from host defences or by providing key nutrients. B. gingivalis has been found to bind fibrinogen (Lantz et al, 1986). binding was rapid, highly specific and saturable. indicated that B. gingivalis The Furthermore, this group possessed a cell-associated thiol protease which 9 could degrade fibrinogen. Winkler et al (1987) investigated the ability of some Gram-positive and Gramnegative oral organisms, membrane-like matrix including B. and to gingivalis, purified fibronectin, laminin and Type IV collagen. to attach to a basement- basement membrane proteins: Their results showed that, generally, the Gram-negative organisms bound in greater numbers to the intact matrix, whereas the Gram-positive organisms attached preferentially to the isolated proteins. Of all the Gram-negative organisms tested, B. gingivalis intact matrix in the greatest numbers and although it did not bound to the bind to a great degree to the isolated proteins, it attached in greater numbers to the isolated Type IV collagen than did either of the other Gram-negative organisms or the Grampositive organisms. The apparent affinity of B. gingivalis for the intact matrix, rather than for the isolated proteins, may be related to involvement of a threedimensional structure of the matrix in adherence. The importance of the binding of B. gingivalis to the isolated Type IV collagen should not be overlooked in that the basement membrane, which is composed of Type IV collagen, offers the last potential barrier to bacterial translocation from the pocket to the underlying connective tissues. 3. Hemagglutination properties The ability of B. gingivalis to hemagglutinate erythrocytes (Boyd and McBride, 1984; Slots and Genco, 1979) differentiate B. gingivalis is an important taxonomic character which can from other Bacteroides species. However, receptor responsible for HA activity has not been completely elucidated. components (capsular polysaccharide and lipopolysaccharide [LPS]) from B, gingivalis extracted from the Surface extracted neither exhibited nor inhibited HA activity, however, pili B. gingivalis Although, as mentioned earlier, did posess HA ability (Okuda et al, 1981). others have had difficulty reproducing this work. 10 Boyd and McBride (1984) showed that the HA activity was associated with lowmolecular-weight LPS, protein, and loosely bound lipid of the outer membrane and furthermore, that procedures which removed fimbriae from the surface of B. had no effect gingivalis upon the ability of the whole cells to cause hemagglutination. In their study, the hemagglutinating activity and the bacterial aggregating activity associated with a crude outer membrane fraction were separated. The fraction responsible for bacterial aggregation comprised a large quantity of protein and carbohydrate with little lipid material, whereas the fraction responsible for hemagglutination contained loosely-bound lipid, carbohydrate and only a small amount of protein. The work of Yoshimura et al (1984) also showed that a preparation of purified fimbriae from B. gingivalis had neither a positive correlation with HA activity nor did it inhibit HA activity. factor of B. Further investigation into the hemagglutination by Okuda et al (1986) resulted in the isolation and gingivalis characterization of a hemagglutination factor from culture supernatant of strain 381. gingivalis mainly of protein B. Their results indicated that the factor was composed (73%) with smaller quantities of sugar (12%) and phosphorous (6%). The apparent molecular weight was 40 kD, as determined by SDS-PAGE. Experimental infections involving asaccharolytic BPBs Asaccharolytic BPB species have often been cited as pathogens in experimental infections (Grenier & Mayrand,1985; Mayrand & McBride, 1980; Gibbons, 1965). Socransky & In these studies, combinations of bacteria were isolated from various oral sources and were tested for their ability to induce abscess formation and transmissible infections when inoculated subcutaneously into guinea pigs. The general consensus from these studies was that individual bacterial species or isolates were not able to induce an infection, however, mixtures of two or more bacteria produced a pathogenic effect. A common finding of these studies was that when BPBs were included in the 11 infectious mixture, a transmissible infection could be produced. the BPB species, and especially asaccharolytic BPBs, mixture, transmissibility was not exhibited. However, when were deleted from the It is possible that the synergistic infective mechanism is related to growth factors produced by the associated bacteria. However, a recent study by Grenier & Mayrand (1987) has shown that six out of fourteen strains of Bacteroides pathogenic in pure culture. gingivalis tested for virulence were These pathogenic strains tended to be highly collagenolytic and proteolytic whereas strains which were not pathogenic had lower collagenolytic activity but possessed a high proteolytic activity. Periodontal diseases Specific periodontal diseases have been described and are distinguished by such factors as the age of the patient, the type and distribution of bone and attachment loss and by the species of bacteria associated with the disease (Page & Schroeder, 1982). For example, adult periodontitis has been associated with BPBs intermedius and B. gingivalis) Slots, 1986a; (Slots,1979; Zambon, 1985; Zambon organisms (Listgarten Capnocytophaga and Actinobacillus Slots & & actinomycetemcomitans, Listgarten, et al, 1981), and 1988; spirochetes Hellden,1978). and Actinobacillus (B. Socransky, 1977; and other motile Bacteroides actinomycetemcomitans gingivalis, have been isolated from patients diagnosed as having juvenile periodontitis (Kornman & Robertson, 1985; Liljenberg & Lindhe, 1980; Moore et al 1985; Newman et al, 1976; Slots, 1976). At least 300 different periodontal pocket. sulcus are bacterial species have been identified within the In health, bacteria comprising the microflora of the gingival primarily Gram-positive, facultative organisms (Slots, 1977a), whereas in adults, a proportionate increase in the number of Gram-negative, anaerobic species occurs as the disease increases in severity (Slots, 1977b; Slots et al, 1978). This is the case as well for juvenile periodonditis where the subgingival microflora has been found to comprise Gram-negative facultative or 12 anaerobic rods (Baehni et al, 1979; Kornman & Robertson, 1985; Moore et al, 1985; Slots, 1976; Tanner et al, 1979). Bacteroides gingivalis has been repeatedly implicated in the establishment and progression of periodontal diseases. Many recent studies have confirmed the finding of Burdon (1928) that Bacteroides species were present in disease sites (reviewed by Slots, 1982; Slots & Listgarten, 1988; van Winkelhoff et al, 1988). B. gingivalis has been recovered not only from sites in adults diagnosed as having generalized advanced periodontitis, (Loesche et al, 1985; Slots, 1977b; Spiegel et al, 1979; Tanner et al, 1979; White & Mayrand, 1981) but also from sites in adult patients which were classified as actively progressing (Slots et al, 1986; Tanner et al, 1984). That periodontal diseases are the result of mixed infections has been the indication from all of the investigations periodontal health and disease. into the microflora related to both The composition of the subgingival flora found in health varies significantly from that found in the various forms of periodontal disease. In a state of health, 95% of the total microflora, as determined by phase contrast or darkfield microscopy, is composed of nonmotile rods and cocci (Listgarten and Hellden, 1978). A s disease progressses, there is a marked decrease in the numbers of cocci and a proportionate increase in the number of motile rods and spirochetes (Lindhe et al, 1980; Temporo et al 1983). Di Murro et al (1987), in a study evaluating the subgingival microflora isolated from patients diagnosed as having rapidly progressive periodontitis, found B. gingivalis to be consistently involved. Furthermore, a recent report by van Dyke et al (1988), indicated that B. gingivalis was an etiologic agent in severe, recurrent adult periodontitis. B. gingivalis has been demonstrated in both generalized juvenile periodontitis (Loesche et al, 1985; Wilson et al , 1985) and in localized periodontitis (Kornman & Robertson,1985; Moore et al, 1985). 13 juvenile Additional evidence periodontal for the role of B. diseases investigators agree comes that from in patients in the various types of gingivalis immunological diagnosed studies. Virtually with generalized periodontitis or adult periodontitis the serum antibody levels to B. are higher than in other groups of individuals ( Altman et al, 1982; al, 1982; Ebersole juvenile gingivalis Ebersole et et al, 1986; Farida et al, 1986; Mouton et al, 1981; Taubman et al, 1982; Vincent et al, 1985). Elevated levels of antibody to B. are also noted in gingival crevicular fluid as compared to serum gingivalis levels (Ebersole et al, 1985; Schonfeld & Kagan, 1982; Tew et al, 1985b). A recent study by Holt et al (1988) indicated that B. successfully implanted into the periodontal could be gingivalis microbiota of monkeys. B. strain 3079.03 was isolated from a ligature-induced periodontal site gingivalis in a cynomolgus gingivalis all strain. monkey and was used to derive a rifampin-resistant Subsequent to the implantation of the had serum antibody levels to the B. gingivalis B. derived strain, not only strain increased as compared to controls, but in addition, significant bone loss was observed radiographically at implanted sites, ostensibly due to a burst of activity. Thus, this work appears to demonstrate a direct connection between the implantation of B. gingivalis and clinical alterations in serum antibody levels and in crestal bone levels. Virulence factors of Bacteroides gingivalis Potentially pathogenic organisms require a combination of properties in order to manifest their effect. B. gingivalis 1. Much research has been directed toward the properties of which contribute to its virulence. Adherence properties One of the first requirements of an organism, in order to initiate disease, is an ability to attach to its host, for only in so doing will the organism be able to colonize and multiply within the host. The features of B. gingivalis which effect adherence have been discussed previously under adherence properties and include 14 fimbriae, hemagglutinins and surface-binding proteins. The recent work by Ohmori et al (1987) and Hanazawa et al (1988) helps to elucidate the virulence properties of the fimbriae of B. gingivalis. (1987) reported that human gingival fibroblasts spontaneously thymocyte-activating factor (FTAF), which in turn stimulates thymoctye proliferation. The importance of Ohmori et al produce mitogen-induced F T A F is that it may function to activate the immune response, which has a potentially damaging effect upon the periodontal tissues of the host. In the follow-up study, Hanazawa et al (1988) examined culture supernatants from gingival fibroblasts for their ability to stimulate thymocyte proliferation. purified fimbriae on F T A F Once this was established, the effect of production was determined by culturing gingival fibroblasts with various doses of purified fimbriae. Lipopolysaccharide was not detected on a silver-stained gel following S D S - P A G E of the fimbriae. results indicated that the fimbriae stimulated F T A F dependent manner. Their production in a dose- Thus fimbriae may have a duel role in the pathogensis of disease: attachment and the activation of factors which elicit a response from the host defense system. 2. C a p s u l e of Bacteroides The capsule of B. gingivalis gingivalis has a number of functions: as a physicochemical barrier between the cell and the external environment, as protection against dessication by binding water molecules, as a defense against the host immune system by avoiding the phagocytic action of polymorphonuclear leukocytes (PMNLs), and if entrapment by PMNLs does occur, the capsule aids in preventing hydrolytic degradation of the organism. The capsule consists of a layer of electron-dense material, external to the outer membrane, approximately 15 nm thick (Handley & Tipler, 1986; Listgarten & Lai, 1979; Woo et al, 1979) and is composed of a polysaccharide heteropolymer (Mayrand & Holt , 1988). Studies relating virulence to the presence of a capsule have shown that those strains which are encapsulated have greater resistance to phagocytosis (Okuda & 15 Takazoe, 1973). Furthermore, when capsular material species was added to a system utilizing Staphylococcus extracted from a BPB aureus, phagocytosis was inhibited. Mayrand & Holt (1988), reviewing the work of van Steenbergen et al (in publication), noted that virulent strains of B. gingivalis killing by human serum and by PMNLs plus serum. organisms did not autoagglutinate, hydrophilic than less virulent strains. that were more resistant to Furthermore, the virulent had a thicker capsule and were more The conclusion from their results was observed differences in virulence can be attributed, at least in part, to differences in capsular structure. 3. The Outer outer membrane membrane vesicles vesicles (previously described) identical, to the outer membrane of B. gingivalis. are similar, if not Their virulence is related to proteolytic and collagenolytic activities, as well as to an ability to hemagglutinate erythrocytes and to promote adherence between noncoaggregating species (Grenier & Mayrand, 1987). Although their role in the pathogenesis of disease is unclear, it is possible that, because of their small size, the vesicles could easily cross epithelial barriers which would be impermeable to whole cells. In this way, the lytic capacity of the cell could be expanded, allowing it to obtain nutrients from a larger area, and creating a pathway for invasion of the whole cell into the tissues. Furthermore, the vesicles could compete for antibodies of the host defence system, thereby impeding the specific antibacterial immune defense (Grenier & Mayrand, 1987). In a study by Smalley & Birss (1987), vesicles from B. were found to have tryspin-like enzyme gingivalis activity, supporting the finding of Grenier & Mayrand (1987) who found not only a trypsin-like, collagenolytic acitvity, associated with the extracellular vesicles. 16 strain W50 but also a In a more recent study by Smalley, Birss & Shuttleworth (1988), a trypsin-like enzyme was purified from a cell- and particle-free culture supernatant of B. gingivalis. The activity was associated with both a 58 kD peptide (by S D S - P A G E ) and a higher molecular-weight complex. Both prepared fractions had the ability to degrade human plasma fibronectin in the presence and the absence of a reducing agent 4. (dithiothreitol). L i p o p o l y s a c c h a r i d e of Bacteroides gingivalis The lipopolysaccharide (LPS) of B. gingivalis is associated with the outer leaflet of the outer membrane and comprises three covalently-linked components: a polysaccharide O antigen which extends into the surrounding medium from the surface of the outer membrane, a core polysaccharide found at the surface of the outer membrane, and the lipid A moiety which is embedded in the outer membrane. The studies of Mansheim & Kasper (1977) and Mansheim et al (1978) indicated that the L P S of BPB species was biochemically different from that of other Gram-negative bacteria in that it lacked heptose and 2-keto-3deoxyoctonate. The absence of these compounds in lipopolysaccharide from BPB species has been disputed (B. Johne, I Olsen, & K. Bryn, J . Dent. Res. abstr. 67:368, 2046,1988). The virulence of L P S from B. gingivalis is manifested in a number of ways: (1) incubation of gingival fibroblasts in culture with L P S inhibits growth of the fibroblasts (Larjava et al, 1987; Layman & Diedrich, 1987), (2) L P S has been shown to cause bone resorption in vitro ( Millar et al, 1986; Nair et al, 1983) and is able to inhibit bone collagen formation (Millar et al, 1986), (3) through induction of interleukin-1, L P S is able to activate the inflammatory response which is postulated to have a role in disease pathogenesis (Hanazawa et al, 1985). 5. Metabolic end-products of Bacteroides gingivalis Other substances which may contribute to the virulence of B. gingivalis the characteristic end-products of asaccharolytic metabolism. 17 include For example, butyric and proprionic acid have been shown to have a cytotoxic effect upon various human or animal cells in culture (Goldstein et al, 1984; Grenier & Mayrand, 1985; Singer & Buchner, 1981; Touw et al, 1982; van Steenbergen et al, 1982). Volatile sulphur compounds, methylmercaptan and dimethyl disulphide, including hydrogen sulphide, produced by B. gingivalis (Tonzetich & McBride, 1981) have a potentially damaging effect upon tissues of the host because they can influence the permeability of the oral mucosal tissues (Ng & Tonzetich, 1983) and can reduce collagen synthesis (Tonzetich & McBride, 1981). Indole and ammonia (MacDonald & Gibbons, 1961; van Steenbergen et al, 1986b) are also potentially toxic metabolic products of B. 6. Enzyme activities a. Perturbation of o f Bacteroides host defense gingivalis. gingivalis mechanisms is able to elaborate specific enzymes which may contribute to its B. gingivalis virulence by destroying or impeding the defensive response of the host immune system. to Carlsson et al (1984a) found the presence of enzymes degrade the macroglobulin. plasma proteinase In vivo, these inhibitors, proteinase which were able 3-1-antitrypsin inhibitors probably and 3-2- function to regulate the activity of proteases released from PMNLs (Starkey & Barrett, 1977), however, the destruction of such inhibitors by B. gingivalis could favor greater tissue degradation and more rapid disease progression. Enzymes which can specifically degrade the plasma proteins albumin, haemopexin, haptoglobulin and transferrin have been reported (Carlsson et al, 1984). The degradation of the iron-transporting requirement of B. gingivalis for hemin. proteins may reflect the Nilsson et al (1985) also found a virulent strain of B. gingivalis (W30) able to recognize and inactivate other important plasma proteinase inhibitors including complement (Cl) inhibitor which is a key modulator of both the classical and alternative pathways of complement activation. 18 Furthermore, antithrombin, plasminogen, complex, clotting factor X and most of the eliminated after 30 minutes of incubation prekallikrein, prothrombinase 2-antiplasmin were functionally with the bacterial suspension. Bacteroides gingivalis is able to alter the host defense system by degrading IgG, IgM and complement factors C3 and C5 (Sundqvist et al, 1985) and secretory IgA (Sato et al, 1987). immunoglobulins Kilian (1981) demonstrated the degradation of A-), A2 and G and in a follow-up investigation (Mortensen 81 Kilian, 1984) purified and characterized an immunoglobulin A1 protease from a B P B species, B. melaninogenicus subsp. melaninogenicus. It may not be possible to compare this work directly with that of either Sundqvist et al (1985) or Sato et al (1987) because the bacterial strain used in the study of Mortensen & Kilian (1984) was a sacchrolytic strain whereas the studies of Sundqvist strains b. The et al (1985) and Sato et al (1987) utilized oral asaccharolytic (B. gingivalis). Provision of nutrients extensive proteolytic enzyme system of B. gingivalis is able to degrade a wide variety of proteinaceous substances. The large number of small peptides produced by protein hydrolysis may then be transported into the cell and used to satisfy its nutritional requirements. c. Destruction of host tissues A strong fibrinolytic activity is evidenced by B. gingivalis (P.A. Mashimo & J . Slots, J . Dent. Res. 62: 663, abstr. 123, 1983; Lantz et al, 1986; Nitzan et al, 1978; Wikstrdm et al, 1983) which provides it with the potential for tissue invasion. Other enzymatic activity may be responsible for the destruction of tissue matrix. The early studies by Courant et al (1965) and Socransky (1970), in which whole plaque samples were analyzed, indicated that the plaque contained lytic enzymes capable of destroying the major components of the gingival connective tissue. More recently, Grenier & Mayrand (1983) investigated the production 19 of enzymes by B. gingivalis which had the potential components of the gingival ground substance. elaborated gingivalis gelatinase, to degrade various Their findings showed that B. chondroitin deoxyribonuclease and fibrinolysis all of which sulfatase, hyaluronidase, may have an effect upon tissue destruction in the pathogenesis of periodontal disease. Gibbons & MacDonald (1961) and Robertson et al (1982) noted the cellassociated collagenase activity of B. gingivalis. This organism has subsequently been shown to be the only BPB species having specific collagenase activity which will degrade native Type 1 collagen (Mayrand & Grenier, 1985; 1987; van Steenbergen & de Graaff, 1986). Sundqvist et al, This type of collagen is the major constituent of gingival connective tissue (From & Schultz-Haudt, 1963) and although it is resistant to many proteolytic enzymes, it can be degraded by both bacterial and mammalian collagenase (Loesche et al, 1982). B. gingivalis Slots, 1981; also possesses a trypsin-like van Winkelhoff et al, 1986c) activity (Laughon et al, 1982; which appears to be an important part of collagen degradation. The trypsin-like activity of B. gingivalis in cultures grown at increasingly (McDermid et al, 1988). strain W50 was found to be enhanced higher pH values, maximal at pH 8.0 Furthermore, the finding of McDermid et al (1988) that collagen degradation required the action of collagenase and a trypsin-like activity emphasizes the importance of these two enzymes in tissue degradation. The trypsin-like activity of B. gingivalis van Winkelhoff (Laughon et al, 1982; Slots, 1981; et al, 1986c) may also contribute to the virulence of this organism by the conversion of latent host collagenase into active collagenase (Golub et al, 1985) and by the activation of the complement system, thereby stimulating prostaglandin-mediated osteoclastic bone resorption 1982). (Schenkein, Unlike eucaryotic collagenases, which cleave native collagen at a single site, collagenase from B. gingivalis hydrolyzes collagen into small peptides 20 (Robertson et al, 1982; Toda et al, 1984), perhaps making the fragments more susceptible to degradation by other, nonspecific proteases. The trypsin-like activity may also contribute to the virulence of B. gingivalis by the induction and activation of host procollagenase (H. Birkedal-Hansen, J . Dent. Res. 62: 101, abstr. S51, 1987). T y p e s of proteases Proteases may be characterized as one or more of the following: 1. serine protease: the active site. characterized by the presence of a unique serine residue at This group includes mammalian trypsin, chymotrypsin and elastase and several bacterial proteases. The usual reaction catalyzed by these enzymes is the hydrolysis of peptide bonds in proteins and peptides. Trypsin cleaves bonds only after lysine and arginine whereas chymotrypsin cleaves bonds only after large hydrophobic residues, eg. tyrosine. protease which is able to degrade elastin. Elastase is a specific Trypsin and chymotrypsin can be inhibited by specific inhibitors which bind to the active site. 2. thiol protease: characterized by the presence of a cysteine side chain at the active site, comparable to the serine residue of a serine protease. Papain is an example of a thiol protease. These proteases can be inhibited by reagents which react with thiol groups or by a variety of metal ions which form complexes with thiol groups. 3. carboxyl (acidic) protease: characterized by the presence of two aspartic acid residues at the active site. These proteases are active at acid pH. Pepsin is a representative of this group and will hydrolyze peptides with hydrophobic residues on either side of the scissile bond. Pepsin can be inhibited by the specific inhibitor, pepstatin. 4. metalloprotease: characterized by the presence of a bound metal (usually 21 zinc) at the active site. These proteases require divalent metal ions for activity. This group of enzymes includes carboxy peptidases A and B (exopeptidases) and thermolysin (endopeptidase). Inhibitors of these proteases include ethylenediaminetetracetic acid and ascorbic acid. Destruction of both hard and soft tissues can occur as a result of the enzyme activities of Bacteroides gingivalis. The major component of the tissues of the periodontium is Type I collagen which, in disease, can be rapidly destroyed (Page & Schroeder, 1976) possibly by both specific collagenase and nonspecific protease activity. The proteases of Bacteroides gingivalis have been the subject of much research. Proteases of Bacteroides gingivalis Uitto & Raeste (1978) determined collagenase activity against Type I collagen using gingival fluid from both healthy and disease sites. This activity was found to be 7 times greater in inflamed versus healthy tissue, however in both groups, collagenolysis was increased by brief exposure to trypsin, suggesting the presence of latent collagenase which could be activated by neutral protease. Collagenase activity was enhanced in both groups by bacterial plaque and by incubation of leukocytes with bacterial plaque extract. In a later study, Uitto (1983) examined the effect upon basement membrane collagen (Type bacterial plaque. IV) using proteinases from human gingiva, leukocytes and As determined by the release of hydroxyproline, the highest activity was found in leukocyte and plaque extracts. Type IV collagen, because of discontinuities in the triple helical structure (Schuppan et al,1980) is susceptible to degradation by nonspecific proteases, for example, gelatinase and elastase-like enzymes. Robertson et al (1982) assessed the collagenolytic activity of a number of oral organisms, including B P B species, Actinobacillus (A.a.), Fusobacterium, Capnocytophaga, 22 actinomycetemcomitans and Selenomonas. Degradation of collagen was determined by S D S - P A G E following incubation of collagen in solution and collagen fibrils with cell sonicates and culture supernatants. These investigators found that the BPB species had a cell-associated collagenolytic activity, whereas collagenolytic activity was observed in both the cell sonicates and media preparations of A.a. Enhancement of the proteolytic activity was found when the cells were grown in peptide-depleted medium. Toda et al (1984), however, did find some collagenolytic activity supernatant from B. gingivalis. in culture The activity was enhanced by the addition of reducing agents such as dithiothreitol (DTT) and L-cysteine, suggesting the presence of a thiol-dependent collagenolytic activity, the production of which increased with bacterial growth (up to 40 hours). The origin of this activity was not precisely defined. The work of Mayrand & Grenier (1985) further elucidated the ability of oral organisms to degrade collagen. including six BPB BPB species, were evaluated. examined, B. gingivalis previously In this study, twelve species of oral bacteria, Their results indicated that, of the was the only species which could degrade collagen sterilized with ethylene oxide. A rapid collagenolysis occurred which was determined to be the result of the combined activity of a specific collagenase and nonspecific proteases. Although other strains were capable of degrading collagen, the hydrolysis was much slower (24 vs 2 hours of incubation) and appeared to be the result of the activity of nonspecific proteases only. The findings of Sundqvist et al (1987) and van Steenbergen & de Graaf (1987) support the results of Mayrand & Grenier (1985). gingivalis These studies also found B. to be the only BPB species, of those examined, to demonstrate specific collagenolytic activity. The results of Sundqvist et al (1987) indicated that the activity was cell-associated. As well as having a specific collagenolytic activity, B. gingivalis has been shown to possess other proteolytic activities, both cell-free and cell-associated, which 23 may be important in the pathogenesis of disease. These nonspecific proteases may produce destruction of tissue directly or may induce factors of the host defense system which can have a deleterious effect upon the periodontal tissues. Fujimura & Nakamura (1981) characterized two partially purified proteases from cell extracts of a strain of B. melaninogenicus. Since the supernatant from an ultracentrifugation following cell sonication was used as the starting material, it is unlikely that the proteases isolated were cell-bound. These proteases were inhibited by thiol compounds, but not by diisopropylfluorophosphate (DFP), an inhibitor of serine proteases. Neither collagenase nor elastase activity was detected. A partially purified protease from B. gingivalis strain 381 was characterized by Yoshimura et al (1984) using the chromogenic synthetic substrate, benzoylD-L-arginine-p-nitroanilide preparation containing (BAPNA). both The activity was found in a whole cell the inner and outer membranes and the peptidoglycan, therefore the exact localization of the enzyme was not possible, although it was classified as being membrane-bound. The trypsin-like activity was inhibited by thiol protease inhibitors and stimulated by reducing agents such as DTT and L-cysteine. Ono et al (1987) also found a trypsin-like protease from culture supernatant of B. activity gingivalis in a partially purified strain 381. These investigators suggested that the activity was due to the same enzyme as previously studied by Laughon et al (1982) and Yoshimura et al (1984). The work by Ono et al (1987) extended the characterization of this protease by determination of the apparent molecular weight by S D S - P A G E to be 49,000 D. It should be noted, however, that the protease studied by Yoshimura et al (1984) was partially purified from a whole cell envelope fraction, whereas Ono et al (1987) used culture supernatant as a starting material. Tsutsui et al (1987) used the supernatant from the ultracentrifugation of 24 sonicated B. gingivalis cells. A protease was isolated and purified by ammonium sulphate precipitaiton and sequential column chromatography. molecular weight by S D S - P A G E was found to be 50,000 D. The apparent This membrane-free protease was inhibited by serine and trypsin inhibitors and was most active at an alkaline pH (8.5). The activity was enhanced by the reducing agents L-cysteine and 2-mercaptoethanol. Although there are similarities to the trypsin-like activity found by Yoshimura et al (1984), this protease was slightly inhibited by M g Mg + + + + and EDTA, whereas significant inhibition from EDTA and activation by was found by Yoshimura et al (1984). In addition, the activity found by Tsutsui et al (1987) was not significantly affected by p-chloromercuribenzoic acid (PCMB), although it did affect the activity of the protease reported by Yoshimura et al (1984). In a later study, Fujimura & Nakamura (1987) examined the characteristics of a trypsin-like protease isolated from a Triton X-100 soluble extract of sonicated cells of B. gingivalis sequential column chromatography. (nonionic detergent) strain 33277 and purified by This enzyme was active at neutral pH (7.5), inhibited by thiol inhibitors and EDTA, with an apparent molecular weight of 65,000 D as determined by S D S - P A G E . The properties of this enzyme are similar to those of the enzyme reported by Yoshimura et al (1984), however, different strains of B. gingivalis were used in each of these studies. Sorsa et al (1987) found both a trypsin-like protease and collagenase in a supernatant fraction resulting from a low speed centrifugation of sonicated cells of B. gingivalis strain 33277. The trypsin-iike protease was able to degrade native Type IV collagen and denatured Type I collagen whereas the collagenase cleaved native Type I collagen at multiple cleavage sites over time. The trypsin- like protease was inhibited by serine protease inhibitors, EDTA, and ascorbic acid; activity was enhanced by reducing agents. The importance of this is that basement membrane is composed of Type IV collagen, thus such a nonspecific, trypsin-like activity could facilitate the penetration of other bacterial toxins and 25 enzymes from the periodontal pocket into the underlying connective tissue. Grenier & McBride (1987) were able to isolate, purify and characterize glycylprolyl protease from the outer membranes of B. gingivalis a strain 33277. The purification was completed by preparative S D S - P A G E and showed a single band with an apparent molecular weight of 29,000 D for the active form of the protease. This protease was inhibited by reducing agents, in contrast to other proteases isolated from B. gingivalis. Proteolytic activity was exhibited against both a synthetic peptide containing the glycylprolyl peptide and denatured collagen. The protease was found in all B. gingivalis strains tested, but not in other BPB species examined. Two groups have investigated the effect of specific peptidases Abiko et al (1985) characterized a partially of B. purified gingivalis. glycylprolyl dipeptidylaminopeptidase isolated from spent culture medium, supernatant from washed cells and supernatant from cell extracts of B. gingivalis strain 381. The enzyme was found to enhance the hydrolysis of partially degraded Type I collagen. Suido et al (1987) isolated two peptidases from the culture supernatant of B. gingivalis strain 381. One, a glycylprolyl peptidase thought to be the same as that found by Abiko et al (1985), was inhibited by serine protease inhibitors. The other enzyme, N-CBz-glycyl-glycyl-arginyl peptidase, was first associated with the cell fraction, but after 48 hours in culture, could be found in the supernatant. This enzyme was characterized as a thiol protease, however, it was not determined whether or not it represented any of the previously described thiol proteases. Finally, Otsuka et al (1987) isolated a protease(s) from culture supernatant from B. gingivalis strain 381. This protease was separated into three isoenzymes, all of which were dependent upon thiol group reagents for activity (DTT). The previous studies of Yoshimura et al (1984), Robertson et al (1982) and Toda et al (1984) suggest the presence of a thiol-dependent 26 trypsin-like protease associated with the proteolytic activity of B. gingivalis. On the basis of their results with specific substrates and inhibitors and the requirement for reducing agents for activity, Otsuka et al (1987) suggest that the designation of this enzyme as a trypsin-like protease be changed to one of a thiol protease. The highly varied and extensive proteolytic nature of B. gingivalis shown in the work of Grenier, Chao, McBride (in press). has been Eight proteases were isolated by these researchers using BSA-polyacrylamide gel electrophoresis. The proteases were isolated, and subsequently characterized, from culture supernatants, cell extracts, purified outer membranes, and outer membrance vesicles. Although only a portion of the proteolytic nature of B. gingivalis can be appreciated from the literature cited, the importance of proteolysis in disease pathogenesis cannot be underestimated, especially as the organism appears to have a direct effect upon the periodontal tissues, and is able to not only induce a response from the host which can enhance disease progression, but can also inhibit the defense system of the host. Proteolytic activity of other pathogenic organisms A number of organisms considered to be pathogenic have been shown to possess cell-associated or cell-free products which are an integral virulence and contribute to their ability to cause disease. Pseudomonas aeruginosa, part of their One such organism is an opportunistic pathogen capable of producing a broad spectrum of disease under a variety of conditions (reviewed by Pollack, 1984). More recently, Heck et al (1986) found Pseudomonas elastase was capable of degrading human collagen, Types III and IV, and that Type I collagen was degraded by both P. aeruginosa elastase and an alkaline protease. Degradation products resulting from the incubation of collagen with the proteases at 25 ° C were visualized Their by staining with Coomassie 27 blue following SDS-PAGE. conclusions were that the tissue destruction observed in P. aeruginosa infections may be the result of collagen degradation by nonspecific extracellular proteases. Collagenolytic activity was observed by Mufioz et al (1984) to be related to the virulence of Entamoeba histolytica. This group had previously shown that E. histolytica produced collagenase which was specific for Type I collagen. Their subsequent study in 1984 examined pathogenic and nonpathogenic strains of E. histolytica. The results indicated that collagenolytic activity correlated positively with the virulence of the organism as determined by the ability of the organisms to produce relationship between liver lesions in hamsters. This evidence for the collagenolysis and virulence is similar to that documented by Grenier & Mayrand (1987) in their study of pathogenic and nonpathogenic strains of Bacteroides gingivalis. The pathogenicity of Legionella pneumophila has been associated with a tissuedestructive protease (TDP) by Williams et al (1987) and Conlan et al (1988). Conlan et al (1988) was able to demonstrate the in vivo production of T D P in the lungs of infected guinea pigs, while the immunocytochemical techniques of Williams et al (1987) demonstrated the presence of T D P in situ. findings reveal an important role for These T D P in the pathogenesis of Legionnaires' disease. An extracellular protease produced by Aeromonas salmonicida is thought to be a virulence factor in the pathogenesis of fish furunculosis. A study by Sakai (1985) demonstrated the importance of the protease in disease by inducing a protease-deficient mutant which, when injected into salmon and trout, produced neither disease nor mortality. Serratia marcesens produces a number of extracellular proteases which are capable of degrading defense-oriented humoral proteins and tissue components. Molla et al (1986) determined that a virulent strain of Serratia produced an extracellular protease which cleaved IgG and lgA1. 28 The protease was not inhibited by endogenous human proteinase inhibitors, 3-1-protease inhibitor and 3-2-macroglobulin, and the inhibitors themselves were completely degraded. Extensive pulmonary edema and hemorrhage was noted by Lyerly & Keger (1983) following administration of a purified protease from Serratia marcescens to the lungs of guinea pigs and mice. The tissue destruction observed was similar to that produced during acute Serratia pneumonia. A i m s of the study All of the organisms described have in common a pathogenic role in specific diseases. The ability of these organisms to produce disease appears to be the result of the associated. combined effects of proteolytic activity, either cell-free or cell- The organism with which this study was concerned was Bacteroides gingivalis and the specific aims of the investigation were to isolate, purify and characterize two membrane-associated proteases. The importance of identifying and characterizing the proteolytic activity of B. gingivalis relates to its presumed role in the pathogenesis and progression of various periodontal diseases. The findings of many investigators potentially of destructive effects B. gingivalis proteases indicate in the form of perturbation of the host defense system and direct tissue destruction. The degradation of host proteins is a potential means by which the organism can satisfy its metabolic requirements. The clinical aspect of the identification of Bacteroides gingivalis proteases is that it may be possible to use specific protease inhibitors in the prevention or treatment of periodontal diseases. 29 MATERIALS and METHODS Bacterial strain and culture conditions 33277, was grown in Brain Heart Bacteroides gingivalis, Infusion broth (3.7%; Difco) hemin (10 ug/ml; Sigma) and vitamin K (1 ug/ml; Sigma). incubated in an anaerobic chamber ( N - H - C 0 2 2 Isolation and purification of proteases 2 strain containing The cultures were [85:10:5]) at 37 ° C . Protease was prepared from the two sources of outer membranes outlined below: Preparation of outer membranes 1. Outer membranes-1 (OM-1): Outer membranes were prepared following the method of Boyd and McBride (1984) and Grenier and McBride (1987). Bacterial cells from Bacteroides centrifugation at 8,000 x g strain 33277, were harvested by gingivalis, from an early-stationary-phase culture. The cells were washed twice in 0.15 M NaCI and suspended in 50 mM phosphate buffer (pH 7.4) containing 0.15 M NaCI. To remove the outer membranes, the cells were sheared through needles of progressively smaller gauge to a final needle size of 26 1/2 gauge. second This was periods. followed by mixing in a Waring blender for seven 30- The blender jar and contents were placed in an ice bath for 2 minutes following each 30-second mixing. The mixture was centrifuged for 20 minutes cells at 8,000 supernatant was x g to remove centrifuged whole for 2 hours and debris. at 80,000 The resulting x g and the gel-like translucent pellets of outer membranes were suspended in distilled water and lyophilized. 2. Outer membranes-2 (OM-2): A cell extract was prepared according to the method of Grenier, Chao, and McBride (in press). Sixty grams (wet weight) of cells treated as described in the previous section (OM-1) were (discontinous sonication, five 3-minute periods, with continuous sonicated cooling in an ice bath, and 2 minute resting periods between each sonication; 30% duty cycle, output 5; Sonifier Cell Disrupter 350; Branson Sonic Power Co.). 30 The sonicated mixture was centrifuged twice (20 minutes at 8,000 x g) to remove cell debris, and the resulting cell extract was concentrated to approximately 1/3 of its original volume by lyophilization. The findings of Grenier, Chao, and McBride (in press) show that the proteolytic activity of the cell extract is identical to that of purified outer membranes and furthermore, this ultracentrifugation. activity can be removed from the cell extract by These findings are good evidence that the activity in the cell extract is due to the presence of outer membrane fragments, and not to soluble proteases unique to this cellular fraction. Preparative 1. polyacrylamide outer membranes-1: of Laemmli proteases. (1970), gel electrophoresis (PAGE) Preparative electrophoresis, with the buffer system was used to accomplish the initial separation of the One hundred mg of lyophilized outer membranes were suspended in 3.5 ml of 50 mM Tris hydrochloride buffer (pH 7.2) and sonicated ( 1 x 1 0 s). The membranes were then solubilized by adding 2.5 ml of sodium dodecyl sulphate (SDS) solubilization buffer (0.125 M Tris hydrochloride, 4% S D S , 20% glycerol, 1% bromphenol blue) and incubating the mixture for 30 minutes at 37 ° C . onto This concentration and volume of outer membrane solution was loaded 6 mm thick, 12% (wt/vol) polyacrylamide resolving gels with 4.5% (wt/vol) polyacrylamide stacking gels. Electrophoresis was carried out at a constant current of 80 mA for two gels, with cooling, for 16 hours (overnight). Following electrophoresis, a narrow vertical strip (approximately 2 cm wide) was cut from one side of the gel and the remainder of the gel stored at 4 ° C . The strip was treated according to the method of Foltmann et al (1985 ) in order to detect proteolytic activity. was washed The gel strip with 2.5% Triton-X 100 in 0.3 M sodium acetate buffer (pH 5.3) for 1 hour to remove S D S . The strip was then equilibrated in the acetate buffer without Triton X-100 for 1 hour. 31 Proteolytic activity was detected by placing the gel strip upon a previously prepared 1% agarose gel containing 1% skim milk and 25 mM dithiothreitol (DTT). proteolytic After incubation for 5-6 hours at 37 ° C , detected as white bands in a clear matrix. activity was Two of these bands, representing protease material, were selected for further purification and characterization (P-1 and P-4). The designations P-1 and P-4 are taken from the work of Grenier, Chao, and McBride (in press) which describes the proteolytic profile of Bacteroides gingivalis. The profiles of the proteolytic activities found in Bacteroides culture gingivalis supernatants, outer membranes, vesicles and cell extracts were analyzed in SDS-polyacrylamide gels containing covalently bound bovine serum albumin. Proteolytic activity of P-1 (M r 200,000 D) and P-4 ( M r 80,000 D) was found in culture supernatants, in cell extracts, in purified outer membranes and in the vesicle preparation of Bacteroides The section of the gel gingivalis . corresponding to proteolytic activity was excised from the remaining gel slab, cut into small pieces and suspended hydrochloride buffer (pH 7.0). constant agitation. in 10 mM Tris The proteins were eluted overnight at 4 ° C with The eluate from P-1 and from P-4 was dialyzed against distilled water for 8 hours at 4 ° C and then lyophilized. The lyophilized eluates (P-1 and P-4) from the preparative electrophoresis procedure were suspended separately in 1.0 ml of 10 mM Tris hydrochloride buffer (pH 7.2). Solubilization of the protein contained in the fractions was accomplished by adding 0.5 ml of SDS-solubilization buffer and incubating the solutions for 30 minutes at 37 ° C . (wt/vol) The solutions were then loaded onto 1.5 mm thick, 10% polyacrylamide resolving gels with 4.5% (wt/vol) polyacrylamide stacking gels and subjected to a second electrophoresis. The electrophoretic purification procedure was carried out at a constant current of 20 mA for two gels, with cooling, for 16 hours (overnight). 32 The areas of proteolytic activity were detected and prepared as described above. The electrophoretic purification procedure was repeated once more using the lyophilized eluate from the previous run as the sample. The partially purified proteases were suspended in 50 mM Tris hydrochloride buffer (pH 7.0) and kept at -20 ° C . 2. outer membranes 2: Aliquots of 5 ml of the cell extract were incubated with 2 ml of the SDS-solubilization buffer for 30 minutes at 37 ° C . The electrophoretic purification procedure was carried out on 6.0 mm gels and 1.5 mm gels as outlined above for outer membranes-1, and the purified protease material suspended and stored in the same manner as that purified from the outer membrane-1 material. The proteases isolated and purified from both OM-1 and OM-2 were used in the characterization studies. All of the results reported, except those for peptidase activity, were obtained from proteases purified from OM-2. Protein determination The amount of protein in the purified fractions and in the crude fractions of OM1 and OM-2 was determined according to the Bradford (Bio-Rad) assay for protein. A standard curve was prepared using bovine serum albumin (BSA) standard stock solution (100 mg/ml; Sigma) diluted with distilled water to 25 pg/ml. Aliquots of this diluted standard solution, containing 0 to 20 u,g of protein, were reacted with 0.2 ml of the Bio-Rad colour reagent and the absorbance measured at A g 5 Protein profiles of OM-1 5 and OM-2 Electrophoresis of OM-1 and OM-2 was carried out on mini-slab gels (0.075 cm thicknesss; Bio-Rad Laboratories, Richmond, Calif.) containing 12% (wt/vol) polyacrylamide in the resolving gel and 4.5% (wt/vol) polyacrylamide in the stacking gel. Two sets of samples were prepared: (i) lyophilized OM-1 and OM-2 were incubated separately with the S D S - solubilization buffer for 30 minutes at 37 ° C (nonboiled fractions), and 33 (ii) lyophilized OM-1 and OM-2 were incubated separately with the SDS- solubilization buffer for 5 minutes at 100 ° C (boiled fractions). Aliquots from both preparations, containing 30 u.g of protein, were loaded onto the gels and electrophoresis carried out at room temperature at a constant current of 200 volts (for two gels). An aliquot containing standard molecular weight proteins was loaded onto the gels as a reference. included serum The reference proteins myosin ([H chain], 200,000 D), phosphorylase b (97,000 D), bovine albumin (68,000 D), ovalbumin (25,700 D) and /Mactoglobulin (43,000 (18,400 D). D), <?-chymotrypsinogen Following electrophoresis, the protein profiles were visualized by staining with silver nitrate following a modification of the procedure of Oakley et al (1980). Protein profiles of P-1 and P-4 The molecular weight of the proteases was determined by S D S - P A G E using 12% (wt/vol) polyacrylamide mini-slab gels. The migration of the proteases was compared to the migration of known protein standards (as described above). Aliquots of each of the proteases were incubated with SDS-solubilization buffer for either 5 minutes at 100 °C, or for 30 minutes at 37 ° C prior to loading onto the gels. Following electrophoresis, the gels were stained with silver nitrate (Oakley et al, 1980). Lipopolysaccharide (LPS) was determined according to the method of Tsai and Frasch (1980). Proteolytic activity of OM-1, OM-2, P-1 and P-4 In addition to the silver stained samples, OM-1 and OM-2 were compared for proteolytic activity, along with an outer membrane vesicle preparation (kindly provided by Dr. Daniel Grenier, University of British Columbia), and the partially purified protease fractions, using the method of Kelleher and Juliano (1984) and D. Grenier & B.C. 1988). Bovine serum polyacrylamide gels to McBride (J. Dent. Res.67:368, abstr. 2045, albumin (BSA) was incorporated provide the substrate for proteolysis. 34 into the SDS- The BSA-acrylamide conjugate was prepared according to the method of Kelleher and Juliano (1984). Four hundred mg of linear polyacrylamide were dissolved in 20 ml of 0.2 M sodium phosphate buffer (PBS), pH 6.8, and then mixed with 8 ml of 25% gluteraldehyde (in water). The mixture was incubated for 24 hours at 37 °C. The non-conjugated gluteraldehyde was removed by dialyzing the mixture against 10 L of distilled water at 4 ° C for four days with three changes of water per day. To the dialyzed mixture 2 ml of 10% BSA (0.2 M PBS, pH 7.2) were added and the mixture allowed to react for 24 hours at 25 °C. Following incubation, the reaction was halted by adding 250 mg of glycine and 3 mg of sodium azide. The mixture was then incubated for 24 hours at 4 ° C and again dialyzed against 10 L of distilled water containing 0.05% sodium azide at 4 ° C for 2 days. The BSA-acrylamide conjugate was stored at 4 °C. Proteolytic activity was determined by analyzing the samples in SDS- polyacrylamide gels containing covalently bound bovine serum albumin (BSA). Briefly, the electrophoresis was carried out as described above, using 10% (wt/vol) polyacrylamide polyacrylamide was in the mixed with resolving gel. BSA-acrylamide Prior to casting, conjugate to the give a concentration of 200 ug of protein per ml of gel (5% [vol/vol] BSA-conjugate in the total casting volume). The crude fractions and partially purified proteases were prepared by incubation with the SDS-solubilization buffer for 30 minutes at 37 ° C . Aliquots of the prepared samples were loaded onto the BSA- polyacrylamide mini-slab gels and subjected to electrophoresis at a constant current of 200 volts (for two gels). Following electrophoresis, the gel was shaken gently for 30 minutes in 100 mM Tris hydrochloride buffer (pH 7.0) containing 2% Triton X-100, washed twice in distilled water and then equilibrated in the Tris buffer without Triton X-100 for 30 minutes. After equilibration, the gel was incubated for 2 hours at 37 ° C in a development buffer of 100 mM Tris hydrochloride (pH 7.0) mM calcium chloride and 50 mM L-cysteine as reducing agent. containing 2.5 The gel was subsequently stained for protein with Coomassie brilliant blue R-250. 35 After destaining, the proteolytic activity could be visualized as clear bands against a dark blue background. Determination of peptidase activity Peptidase activity was determined according to the method of Berdal and Olsvik (1983). Each of the proteases was incubated with each of the chromogenic peptides in the same manner as outlined below for the BAPNA (N-<?-Benzoyl-Darginine-p-nitroanilide) assay: Briefly, 75 pi of each of the proteases was incubated with 75 uJ of a 2 mM solution of each of the chromogenic peptides in a reaction mixture containing 225 u_l of 50 mM Tris hydrochloride buffer (pH7.5 at 37 °C) and 2 mM DTT . Incubation was carried out overnight at 37 ° C , following which, p-nitroaniline was measured after diazotization. the release of Trichloroacetic acid (40% in water, 375 pi) was added to the mixture followed by 112.5 u.l of freshly prepared sodium nitrite (0.1% in water). temperature, 112.5 pi of sodium sulphamate After 5 minutes at room (0.5% in water) was added and the reaction mixture incubated for 5 minutes at room temperature. Lastly, 112.5 uJ of freshly prepared N-1-naphthylethylene diamine dihydrochloride (0.1% in water) was added and following 5 minutes incubation at room temperature, the absorbance at A 5 4 5 was recorded. The diazotization procedure alters the absorption maxima and increases the sensitivity of the test. Determination of peptidase activity was semi-quantitave based upon the following scale: no colour reaction (0), faint red colour (+/-), clearly visible red colour (+), strong red colour (++). Determination of optimum pH A reaction mixture was prepared containing 75 u.l of the partially purified proteases (P-1, 1.7 u,g total protein; u.l of 2 mM P-4, 1.1 pg total protein), 75 N-<?-Benzoyl-D-arginine-p-nitroanilide 36 (BAPNA) and 225 u.l of one of the following buffers: 0.2 M acetate buffer, pH 4.8 and 5.4; 0.2 M phosphate buffer, pH 5.6 to 8.1; 0.2 M Tris hydrochloride buffer, pH 7.0 to 8.6. Each of the buffers contained sufficient DTT such that the reaction mixture was 2 mM in DTT. The reaction mixture was incubated overnight at 37 ° C and the release of p- nitroaniline was measured after diazotization as outlined above for the BAPNA assay. Determination of optimum temperature and heat stability Using the BAPNA assay outlined above, the optimum temperature for activity was determined by incubating the substrate overnight with the proteases in a sample mixture containing 50 mM Tris hydrochloride buffer, pH 7.5, and 2 mM DTT. The incubation was carried out at 25, 30, 37, 45 ° C . The heat stability of the proteases was determined as above, except that the protease used (P-4) was incubated at temperatures of 4, 37, 55, 80, and 100 ° C for 30 minutes, 2 hours or 24 hours prior to determination of enzyme activity using the BAPNA assay. Inhibition of protease activity Protease activity was determined in the presence of various protease inhibitors and metal ions: EDTA, N-9-p-tosyl-L-lysine phenylmethylsulfonyl fluoride (PMSF), chloromethyl ketone tosylamine-2-phenyIethyIchloromethylketone p-chloromercuribenzoic hydrochloride (TLCK), L-1- (TPCK), S D S , iodoacetate, acid (PCMB), aprotinin, C a C I , HgCI , MgCI , Z n C I . 2 2 2 2 Each of the purified proteases was incubated with each of the inhibitors for 30 minutes at 37 ° C prior to determination of protease activity using the BAPNA assay . A positive control containing protease, substrate and buffer with DTT, but no inhibitor, was taken to be 100% reactive. The relative reactivity of the proteases following incubation with each of the selected inhibitors was calculated on this basis. 37 Hydrolysis of protein substrates by P-1 and P-4 Proteolytic activity against azocoll and azoalbumin was determined according to the method of Mayrand and McBride (1980). azocoll assay contained 15 u.l of purified The reaction mixture for the protease, 50 u.l of azocoll (30%), 450 pi of 50 mM Tris hydrochloride buffer (pH 7.5 at 37 °C) and 2 mM DTT. The mixture was incubated overnight at 37 °C, subsequently centrifuged at 12,000 x g for 3 minutes and the absorbance of the supernatant read at A 5 8 0 A sample . mixture containing azocoll, buffer and DTT served as the control. The reaction mixture for the azoalbumin assay contained 100 u.l of purified protease, 500 u1 of azoalbumin (3% in 50 mM Tris hydrochloride buffer, 7.5 at 37 °C), and 25 mM DTT. pH The mixture was incubated overnight at 37 ° C . Following the incubation, 500 u.1 of 20% trichloroacetic acid (TCA) was added to stop the reaction and the resulting 12,000 x g material) A 3 7 5 . for 3 minutes. To precipitate was removed by centrifuging the resulting supernatant at (TCA-soluble 150 pi of 6 N NaOH was added, and the resulting absorbance read at A sample mixture containing azoalbumin, buffer and DTT served as the control. Proteolysis of IgA, IgG, gelatin, and acid-soluble collagen was determined by assaying for lower-molecular-weight degradation products by S D S - P A G E . The proteins in question were incubated overnight at 37 ° C in a reaction mixture containing 25 uJ of partially purified protease, 25 u,l of protein substrate (1 mg/ml), 25 u.l of mM DTT. 50 mM Tris hydrochloride buffer (pH 7.5 at 37 °C), and 2 Subsequently , the samples were incubated for 5 minutes at 100 ° C with 20 u.l of SDS-solubilization buffer. loaded onto mini-slab gels Aliquots of each of the samples were containing an concentration to assay for degradation products. were stained with Coomassie prepared appropriate polyacrylamide After electrophoresis, brilliant blue R-250. the gels Control samples were containing the same reaction mixture but these were not incubated at 37 °C, instead solubilization buffer was immediately added to the samples and the 38 mixtures incubated for 5 minutes at 100 ° C . Determination of immunoreactivity The antibody used in this determination was prepared Dr. Daniel Grenier, University of British Columbia. membrane-associated Bacteroides gingivalis and kindly provided by The antibody was against a glycylprolyl protease (Grenier and McBride, 1987) and did not contain antibody against lipopolysaccharide. Cross-reactivity between the partially purified proteases (P-1 and P-4) and the prepared antibody was determined by Western blotting (Burnette, 1981). Electrophoresis was carried out as described above on a 12% (wt/vol) polyacrylamide resolving gel onto which had been loaded aliquots of P-1 (0.68 u.g of total protein), P-4 (0.45 u.g of total protein), crude OM-1 (20 u.g of total protein), crude OM-2 (20 u,g of total protein) and outer membrane vesicles (10 u.g of total protein). After the run, electrophoretic blot transfer of material was conducted according to the method of Burnette (1981). The gel was placed upon three layers of 3M Whatman filter paper buffer (glycine [14.4 g/L], Tris previously wetted in the blotting hydrochloride ml/L], pH 8.3). Nitrocellulose paper, previously [3.02 g/L], methanol [200 wetted in Tris buffered saline (TBS; 20 mM Tris hydrochloride, 0.5 M NaCI; pH 7.5) was placed upon the gel and another three layers of wetted filter paper placed over the nitrocellulose paper. The whole stack was placed into the holding cassette of the Bio-Rad Blot cell (Bio-Rad Laboratories, Richmond, Calif.) and the cell filled with blotting buffer. Electrophoretic transfer was carried out for 2 hours at room temperature with a constant current of 60 volts. Following electrophoresis, the nitrocellulose was first shaken gently with blocking buffer (3% BSA) for 1 hour, and then with the first antibody (anti-glycylproyl protease, 1:400 in 1% BSA) for 1 hour. incubation with the first antibody, the nitrocellulose was water followed by washing for 20 minutes 39 After washed with distilled in 2-100 ml changes of T B S containing 0.05% Tween-20 (TTBS). Subsequently, the nitrocellulose was shaken gently with the second antibody (goat anti-mouse IgG horseradish peroxidase conjugate [Bio-Rad], 1:3000 in 1% BSA) for 1 hour, followed by washing in distilled water and T T B S as outlined above. Staining of the antigen- antibody complexes with antibody raised in rabbit to the glycylprolyl protease was carried out with the Bio-Rad Immun Blot (GAR-HRP) assay kit. Chemicals Synthetic peptides, IgG, IgA, azocoll, azoalbumin , acid-soluble collagen and the protease inhibitors P M S F , T P C K , TLCK, P C M B were purchased from Sigma. Electrophoresis chemicals (glycine, SDS, acrylamide, bis-acrylamide, ammonium persulfate and TEMED) were purchased from Bio-Rad. 40 RESULTS Purification Comparison of OM-1 and The yield of purified OM-2. outer membranes was 233 mg, dry weight, (7.8 mg per liter of culture) in one preparation, from an original wet weight of cells of 104 gm (3.5 gm per liter of culture). In a second preparation, 560 mg, dry weight, (14.0 mg per liter of culture), of outer membranes were purified from an original wet weight of cells of 155 gm (3.9 gm per liter of culture). The protein content of the outer membrane fractions was determined to be 1.5 mg/ml; the cell extract contained 2.0 mg/ml of protein. The protein profile of the outer membrane preparation (OM-1) obtained by silver staining (Fig. 1) was similar to that previously reported in Boyd & McBride (1984) and Grenier & McBride (1987). The pattern was similar, but not identical, to that of a cell extract prepared by sonication, as outlined in Materials and Methods for outer membranes-2 (OM-2, Fig. 2). bands revealed in the profile of OM-2 had the same M r The major as those of OM-1, the differences being in the number and intensity of staining of the minor bands. An apparent difference is the absence of several low molecular weight bands in the protein profile of OM-2 (Fig. 2, lanes E, F, G, H ) as compared to the protein profile of OM-1 (Fig. 1, lanes E, F, G, H). The low molecular weight bands are not visible in either the boiled or nonboiled samples of OM-2 (Fig. 2, lanes E, F, G, H). A possible explanation is that the integrity of the proteins in OM-1 are preserved whereas the proteins in OM-2 are subjected to proteolytic activity from proteases released during cell sonication. Electrophoresis and silver staining of boiled samples of both OM-1 and OM-2 produced major bands corresponding to M o f 68 kD , 45 kD and 40 kD. r corresponding to M r A number of minor bands both higher and lower than these major bands were apparent. 41 Electrophoresis followed by silver staining of the nonboiled samples revealed a major band corresponding to an M o f 45 kD in the OM-1 preparation (Fig. 1, r lanes B and F) and a similar major band corresponding to 40 kD in the OM-2 preparation (Fig. 2, lanes B and F). These major bands were also found in the respective protein profiles of the boiled samples (Figs. 1 and 2, lanes A and E). In Figures 1 and 2, lanes C, D, G, and H show the protein profiles of the boiled and nonboiled samples following solubilization in buffer containing reducing agent (5-mercaptoethanol). When compared with the protein profiles of the boiled and nonboiled samples (Figs.1 and 2, lanes A, B, E, F) solubilized in buffer without reducing agent, it apparent that there are fewer bands in those lanes which contain samples solubilized in buffer containing reducing agent (Figs. 1 and 2, lanes C, D, G, H), most noticeable when comparing lanes F and H. It is likely that the reducing agent is able to protect the sulfhydryl bonds in the proteases, thus resulting in fewer visible bands. The skim milk zymogram obtained following preparative gel electrophoresis of OM-1 and OM-2 revealed three proteolytic bands with apparent weights above 68,000 D (Fig. 3). molecular The bands were not similar in their intensity of activity, the lower molecular weight band (P-4) and the intermediate band having more activity against the casein substrate than the higher molecular weight band (P-1). The relative intensity of the bands was consistent from one preparation to another. P-1 and P-4 were selected for further purification and characterization. 42 Figure 1. SDS-PAGE of outer membrane-1 preparation. Lane A: boiled OM-1, 0.2 ug dry weight, SDS-sol buffer* Lane B: nonboiled OM-1, 0.2 ug dry weight, SDS-sol buffer Lane C: boiled OM-1, 0.2 u.g dry weight, /J-ME-sol buffer** Lane D: nonboiled OM-1, 0.2 ug, dry weight, /3-ME-sol buffer Lane E: boiled OM-1, 2.0 ug dry weight, SDS-sol buffer Lane F: nonboiled OM-1, 2.0 ug dry weight, SDS-sol buffer Lane G : boiled OM-1, 2.0 ug dry weight, tf-ME-sol buffer Lane H: nonboiled OM-1, 2.0 ug dry weight, /3-ME-sol buffer * sodium dodecyl sulfate solubilization buffer ** fl-mercaptoethanol solubilization buffer Arrows indicate molecular weight markers, from top to bottom, respectively: 97,000 D (phosphorylase b) 68,000 D (bovine serum albumin) 43,000 D (ovalbumin) 25,700 D (<9-chymotrypsin) 43 43a Figure 2. SDS-PAGE of outer membrane-2 preparation. Lane A: boiled OM-2, 0.1 x 10" ug total protein, SDS-sol buffer* 3 Lane B: nonboiled OM-2, 0.1 x 10' ug total protein, SDS-sol buffer** 3 Lane C: boiled OM-2, 0.1 x 10" ug total protein, 3 Lane D: nonboiled OM-2, 01. x 1 0 -3 fl-ME-sol buffer ug total protein, /?-ME-sol buffer Lane E: boiled OM-2, 1.0 x 10~ ug totall protein, SDS-sol buffer 2 Lane F: nonboiled OM-2, 1.0 x 1 0 -2 ug total protein, SDS-sol buffer Lane G : boiled OM-2, 1.0 x 10" ug total protein, 2 Lane H: nonboiled OM-2, 1.0 x 1 0 -2 fl-ME-sol u.g total protein, buffer tf-ME-sol buffer * sodium dodecyl sulfate solubilization buffer tf-mercaptoethanol solubilization buffer Arrows indicate molecular weight markers, from top to bottom, respectively: 97,400 D (phosphorylase b) 68,000 D (bovine serum albumin) 43,000 D (ovalbumin) 25,700 D (<9-chymotrypsin) 44 44a Figure 3. Zymogram of proteases after preparative SDS-PAGE. 45 45a Proteolytic activity of samples against bovine serum albumin (BSA) The protocol outlined in Materials and Methods for the detection of proteolytic activity on BSA-polyacrylamide gels was selected following a number of experiments to determine the optimum length of time for treatment of the gels in Triton-X-100 and for the incubation of the gels in the development buffer. The test gels were subjected to treatment times in Triton X-100 of 15, 30, 60 or 120 minutes whereas the incubation times in development buffer were from 0.5,1.5, 2.0 to 5.0 hours. volume varied The optimal concentration of BSA in the casting was determined to be 5% after testing the protocol using gels containing 4, 5 or 15% BSA-conjugate (vol/vol) in the total casting volume. The optimal treatment time in Triton-X-100 was 30 minutes whereas the optimal incubation time in development buffer was 2 hours. Determination of total protein After the third preparative P A G E , the amount of protein contained in the proteases purified from the OM-1 preparation was determined according to the Bradford (Bio-Rad) protein assay, and found to be 1.2 mg/ml (P-1) and 1.6 mg/ml (P-4), whereas the same proteases purified from the OM-2 preparation contained 67.5 u,g/ml (P-1) and 45.0 pg/ml (P-4). found in P-1 and P-4 The lower protein content purified from the OM-2 preparation is not unexpected in that the cells used to obtain the extract had been previously stripped, to a large degree, of the outer membranes with which the proteases are associated. Specific activity of P-1 and P-4 The purification procedures resulted in an increase of specific activity and 40-fold respectively greater than that of the (Table 1). 46 OM-2 preparation, P-1 45-fold and P-4, T A B L E 1. Purification of P-1 and P-4 from the OM-2 preparation of Bacteroides gingivalis 33277 Fraction Protein Total Sp act Purifi- Yield (mg) units* U/mg of cation (%) protein OM-2 20 6.0 0.3 1 100 P-1 0.067 0.9 13.4 45 15 ** P-4 0.067 0.8 1 1.9 40 13 ** One unit of enzyme activity is defined as the amount of enzyme which released I (xmol of p-nitroaniline from 2 mM B A P N A in 120 minutes at 37 ° C . This is not necessarily the true yield since the original preparation contained a number of BAPNA-degrading proteases. Following the second S D S - P A G E purification, the protein profile of boiled P-1 revealed one major band corresponding to an M r 68 kD and six minor bands corresponding to M f r o m approximately 50 to 18 kD (Fig. 4, lane E) whereas r nonboiled P-1 revealed three major bands corresponding to M in the range of r 200 kD and one minor band with an M o f approximately 50 kD (Fig. 4, lane F). r The 50 kD samples. band was present in the profiles of both the nonboiled and boiled The bands were visualized by silver staining the gels after electrophoresis. Following the third and final S D S - P A G E purification, electrophoresis of boiled P-1 produced five bands which corresponded to molecular weights ranging from 68 kD (major band) to 18 kD (Fig.4, lane G). major bands following electrophoresis. Nonboiled P-1 produced three The bands obtained after silver staining corresponded to molecular weights of 235 kD, 220 kD, and 200 kD (Fig. 4, lane H). 47 After the second S D S - P A G E purification, electrophoresis of boiled P-4 produced eight bands corresponding to M r of 68 to 18 kD (Fig. 5, lane E) whereas nonboiled P-4 revealed one major band corresponding to an M of 200 kD (Fig. r 5, lane F). After the third and final S D S - P A G E purification, electrophoresis of boiled P-4 produced two major bands which corresponded to molecular weights of 68 and 50 kD, and a minor band corresponding to 40 kD (Fig. 5, lane G). Nonboiled P-4 produced one major band following electrophoresis which corresponded to a molecular weight of 74 kD (Fig. 5, lane H). The three bands produced following electrophoresis of the boiled P-4 (68, 50, 40 kD) were also present in the protein profile of boiled P-1 (Fig. 4, lane G). The M r of the partially purified proteases determined by silver staining correlated well with the bands of proteolytic activity found in gels in which BSA had been incorporated as a substrate for the proteases (Fig. 6). Proteolytic activity can be visualized (Fig. 6, lanes C and D) in the area of 200 kD (P-1) and at 74 kD (P-4; Fig. 6, lane B). Lane D contains protease (P-1) eluted from the upper one-half of a gel section excised from a preparative gel whereas Lane C contains protease (P-1) eluted from the lower one-half of the same preparative gel section. If the two were combined, it would be equal to the whole P-1 protease as visualized following silver staining in Figure 4. No bands were detected following electrophoresis of the purified proteases and subsequent staining of the gels for lipopolysaccharide. 48 Figure 4. SDS-PAGE of P-1. Lane A: boiled OM-1, 2.0 ug dry weight, SDS-sol buffer* Lane B: nonboiled OM-1, 2.0 u.g dry weight, SDS-sol buffer Lane C: boiled P-1, after preparative S D S - P A G E , SDS-sol buffer Lane D: nonboiled P-1, after preparative S D S - P A G E , SDS-sol buffer Lane E: boiled P-1, after 2nd purification by S D S - P A G E , SDS-sol buffer Lane F: nonboiled P-1, after 2nd purification by S D - P A G E , SDS-sol buffer Lane G : boiled P-1, 0.2 u.g total protein, after 3rd purification by S D S - P A G E , SDS-sol buffer Lane H: nonboiled P-1, 0.2 u.g total protein, after 3rd purification by SDS-PAGE, SDS-sol buffer sodium dodecyl sulfate solubilization buffer Arrows indicate molecular weight markers, from top to bottom, respectively: 200,000 D (myosin, H chain) 97,000 D (phosphorylase b) 68,000 D (bovine serum albumin) 43,000 D (ovalbumin) 25,700 D (^-chymotrypsin) 18,400 D (/3-lactoglobulin) 49 A B C D E F HI 49a G H jm Figure 5. SDS-PAGE of P-4. Lane A: boiled OM-1, 2.0 u.g dry weight, SDS-sol buffer* Lane B: nonboiled OM-1, 2.0 u.g dry weight, SDS-sol buffer Lane C: boiled P-4, after preparative S D S - P A G E , SDS-sol buffer Lane D: nonboiled P-4, after preparative S D S - P A G E , SDS-sol buffer Lane E: boiled P-4, after 2nd purification by S D S - P A G E , SDS-sol buffer Lane F: nonboiled P-4, after 2nd purification by S D S - P A G E , SDS-sol buffer Lane G : boiled P-4, 0.2 ug total protein, after 3rd purification by S D S - P A G E , SDS-sol buffer Lane H: nonboiled P-4, 0.2 u.g total protein, after 3rd purification by SDS-PAGE, SDS-sol buffer * sodium dodecyl sulfate solubilization buffer Arrows indicate molecular weight markers, from top to bottom, respectively: 200,000 D (myosin, H chain) 97,000 D (phosphorylase b) 68,000 D (bovine serum albumin) 43,000 D (ovalbumin) 25,700 D (<9-chymotrypsinogen) 18,400 D (/Mactoglobulin) 5 0 A B C D E 50a F G H Figure 6. Proteolytic purity of OM-2, P-1 and P-4. Lane A: nonboiled OM-2, 30 u.g total protein, SDS-sol buffer * Lane B: nonboiled P-4, 0.22 u.g total protein, SDS-sol buffer Lane C: nonboiled P-1 (lower 1/2), 0.45 ug Lane D: nonboiled P-1 (upper 1/2), 0.45 ug total protein, SDS-sol buffer Lane E: total protein, SDS-sol buffer molecular weight markers, from top to bottom, respectively: 200,000 D (myosin H chain) 97,400 D (phosphorylase b) 68,000 D (bovine serum albumin) 43,000 D 25,700 D (ovalbumin) (<9-chymotrypsinogen) * sodium dodecyl solubilization buffer 51 A B C 51a D E Peptidase activity Peptidase activity is shown in Table 2. There was no proteases regarding peptidase activity. Both were able to readily hydrolyze substrates containing benzoyl-arginine groups: arginine-p-NA and the glutamylglycyl-L-arginine-p-NA. L-Pro-p-NA the dipeptide, N-3-Benzoyl-D- tetrapeptide, N-Benzoyl-L-isoleucyl-L- The two dipeptides containing glycine, and Gly-L-Arg-p-NA aminopeptide L- difference between the Gly- , were less actively hydrolyzed, and the -glutamyl-p-NA was only weakly degraded. T A B L E 2. P e p t i d a s e activity of P-1 a n d P-4 Substrate P-1 Activity* P-4 Activity* L-Alanine-p-N A 0 0 L-Arginine-p-N A 0 0 L- o'-Glutamyl-p-N A + / - +/- L-Leucine-p-N A 0 0 L-Lysine-p-N A 0 0 L-Methionine-p-N A 0 0 L-Proline-p-N A 0 0 L-Valine-p-N A 0 0 + + + + + / - + / - + + 0 0 + + + + 0 0 N-3-Benzoyl-D-arginine-p-N A Glycyl-L-proline-p- N A Glycyl-L-arginine-p-N A L-Alanyl-L-alanyl-Lphenylalanine-p-NA N - B e n z o y l - L - i s o l e u c y I-Lglutamylglycyl-L-arginine-p-N A Methoxysuccinyl-L-alanyl-L-alanylL- proline-L-valine-p-N A * T h e d e t e r m i n a t i o n of p e p t i d a s e activity on s y n t h e t i c s u b s t r a t e s w a s s e m i - q u a n t i t a t i v e b a s e d u p o n t h e f o l l o w i n g s c a l e : no c o l o u r r e a c t i o n (0), faint r e d c o l o u r (+/-), c l e a r l y v i s i b l e red c o l o u r (+), strong red c o l o u r (++). 52 Optimum pH The optimum pH for activity of both proteases was found to be between pH 6.0 and 6.5, although there was significant activity over the pH range of 5.5 to 7.0 (Figs. 7 and 8). Both proteases appeared to have significant activity in the acetate buffer whereas Optimum activity appeared to be inhibited in Tris hydrochloride buffer. temperature As determined by the BAPNA assay, the optimum temperature for activity for both proteases was found to be 37 ° C (Fig. 9). Activity declined at temperatures either higher or lower than this value. P-4 appeared to be much more sensitive to changes in temperature than did P-1. 90% At 45 °C, P-1 retained approximately of the relative reactivity whereas P-4 had only 45% of the relative reactivity at the same temperature. reactivity whereas P-1 At 25 °C, P-4 exhibited 42% of the relative retained 47% of the relative activity at the same temperature. Heat stability P-4 was used as the representative sample to determine the heat stability of the partially purified proteases, based upon its apparent sensitivity to changes in temperature. The proteolytic activity of P-4 was completely incubation at 80 ° C or after boiling for 5 minutes. abolished after 2 hours of Incubation at temperatures below 55 ° C for 30 minutes or for 2 hours had relatively little effect upon proteolytic activity and 41% of the relative activity was retained after 16 hours of incubation at 55 °C. Electrophoresis of P-4 which had been incubated at 37 ° C for 48 hours revealed autodegradation. This could be visualized, following silver staining, as a loss of 53 resolution of the protein bands when compared to those of the non-incubated control (Fig. 10). The major band (Fig. 10, lanes A, C, E) corresponds to the 74 kD band seen in Figure 5 (lane H) following electrophoresis of nonboiled P4. The major bands (Fig. 10, lanes B, D, F) correspond to the 68, 50, and 40 kD bands seen in Figure 5 (lane G) following electrophoresis of boiled P-4. Comparison of the bands in Lanes B, D, and F (Fig. 10) reveals the loss of the 50 kD band in Lane D (boiled P-4, incubated 48 hours at 37 °C). The loss of this band indicates autodegradation of the P-4 protease after this incubation period. The protease remained stable for at least 3 months at -20 ° C ; repeated freezing and thawing had no apparent effect upon proteolytic activity. 54 Figure 7. Optimum pH for the hydrolysis of B A P N A by P-1. The reaction mixture contained 75 u,l of purified P-1, 75 u.l of 2 mM BAPNA, 225 U.I of buffer, and 2 mM DTT. buffer, pH 4.8 and 5.4; The following buffers were used: 0.2 M acetate 0.2 M phosphate buffer, pH 5.6 to 8.1; 0.2 M Tris hydrochloride buffer, pH 7.0 to 8.6. The reaction mixture was incubated overnight at 37 ° C and the release of pnitroaniline was measured after diazotization as outlined for the BAPNA assay in Materials and Methods. 55 55a Figure 8. Optimum pH for the hydrolysis of B A P N A by P-4. The reaction mixture contained 75 u.1 of purified P-4, 75 u.1 of 2 mM BAPNA, 225 u.1 of buffer and 2 mM DTT. buffer, pH 4.8 and 5.4; The following buffers were used: 0.2 M acetate 0.2 phosphate buffer, pH 5.6 to 8.1; 0.2 Tris hydrochloride buffer, pH 7.0 to 8.6. The reaction mixture was incubated overnight at 37 ° C and the release of pnitroaniline was measured after diazotization, as outlined for the BAPNA assay in Materials and Methods. 56 56a F i g u r e 9. O p t i m u m t e m p e r a t u r e for the h y d r o l y s i s of B A P N A b y P-1 a n d P-4. The reaction mixtures contained 75 u.l of either P-1 or P-4, 75 u.l of 2 mM BAPNA, 225 u.1 of Tris hydrochloride buffer, pH 7.5 and 2 mM DTT. reaction mixtures were incubated overnight at the following temperatures: The 25, 30, 37, and 45 ° C . The release of p-nitroaniline was measured after diazotization as outlined for the BAPNA assay in Materials and Methods. 57 110 -i Temp. 57a Figure 10. Heat stability of P-4. Lane A: nonboiled P-4, incubated 48 hours at 4 ° C Lane B: boiled P-4, incubated 48 hours at 4 ° C Lane C: nonboiled P-4, incubated 48 hours at 37 ° C Lane D: boiled P-4, incubated 48 hours at 37 °C Lane E: nonboiled P-4, control maintained at -20 ° C Lane F: boiled P-4, control maintained at -20 ° C Lane G: molecular weight markers: 97,400 D (phosphorylase b) 43,000 D (ovalbumin) 25,700 D (3-chymotrypsinogen) 58 58a Inhibition of enzyme activity The effect of various inhibitors and metal ions on the hydrolysis of BAPNA is shown in Table 3. The proteases were strongly inhibited by the chymotrypsin inhibitor T P C K , and by the thiol inhibitors P C M B , iodoacetate and Hg ions. Inhibition occurred to a lesser extent from the serine protease inhibitor PMSF, from the trypsin inhibitor TLCK, from the anionic detergent S D S , and from Zn ions, which are inhibitory to thiol proteases. The activity of the proteases against BAPNA was enhanced by EDTA, aprotinin, and C a and Mg ions. T A B L E 3. Compound Effect of protease inhibitors a n d metal ions on e n z y m e activity Concn P-1 % R e s i d u a l (mM) activity None P-4 % R e s i d u a l activity 100 100 EDTA 20 304 241 PMSF 4 44 85 TLCK 2 44 41 TPCK 2 8 7 20 50 29 PCMB 4 2 0 Iodoacetate 2 0 9 8 ]ig/ml 318 234 2 217 203 2 2 1 2 323 347 2 74 60 SDS Aprotinin CaCI 2 HgCI 2 MgCI ZnCI 2 2 * Activity w a s m e a s u r e d by the B A P N A a s s a y a s outlined in Material and M e t h o d s . 59 Activity against protein substrates The activity of the proteases against protein substrates is shown in Table 4. Both of the proteases were able to degrade gelatin, IgA, IgG and the two azo substrates, azocoll and azoalbumin, under the conditions of the experiments. Acid-soluble collagen was not hydrolyzed by either protease during overnight incubation at 25 °C. T A B L E 4. Substrate Proteolytic activity of P-1 and P-4 P-1 Activity* P-4 Activity* Azocoll + + Azoalbumin + + Gelatin* + + IgG* + + IgA* + + Acid-soluble collagen* * T h e d e t e r m i n a t i o n of activity a g a i n s t p r o t e i n s w a s b a s e d u p o n the ability of the p r o t e a s e s to p r o d u c e fragments of lower molecular weight a s c o m p a r e d to the original protein profile s e e n in p o l y a c r y l a m i d e gels stained with C o o m a s s i e blue. The degradation of IgA and IgG is apparent (Fig. 11) as a loss of bands following overnight incubation (37 ° C ) of the substrates with the proteases (Fig. 11, lanes B, D, F, H) as compared with the IgA and IgG samples which were not incubated with the proteases (Fig. 11, lanes A, C , E, G). Gelatin was completely degraded by both P-1 and P-4 (Fig. 12). The degradation is indicated by the loss of bands (Fig. 12, lane B, gelatin with P-1 and lane F, gelatin with P-4) following overnight incubation (37 ° C ) of the substrate with the proteases as compared to the profiles seen in lanes A and E (Fig. 12) which contain samples of non-incubated substrate and protease. The 68 kD band seen in 60 lanes A, B, C, and D (Fig. 12) may be a contaminant related to the P-1 protease rather than to the substrate, since it appears to remain unaltered following the overnight incubation. It was initially thought that P-1 had collagenolytic activity since acid-soluble collagen was completely degraded following overnight incubation with the protease at 37 ° C (Fig. 12, lane D). Therefore, a subsequent experiment, having a reaction mixture which comprised acid-soluble collagen, boiled P-1, a nonspecific protease (trypsin), Tris hydrochloride buffer and DTT, was completed following identical experimental conditions. After electrophoresis of the samples, it was evident that collagenolysis had occurred in the presence of trypsin and boiled Fraction 1 (Fig. 13, lane B). Since boiling was previously shown to completely abolish the proteolytic activity of the purified protease, the degradation which occurred could not be the result of proteolytic activity due to P-1. The results suggest that the non-specific protease (trypsin) was responsible for the collagenolytic activity in concert with the disruption of the helical structure of collagen which occurs at 37 ° C (Fig. 13, lane B). The collagenolytic activity of the nonboiled P-1 could be the result of a similar effect upon acid-soluble collagen during incubation at 37 ° C . Alternatively, this could result from a small amount of residual S D S in the P-1 protease which may disrupt the tertiary structure of the collagen making it accessible to a non-specific protease. 61 molecule, Figure 11. Lane A: Hydrolysis of immunoglobulins P-1 with IgA, T A and G by P-1 and P - 4 . 0 Lane B: P-1 with IgA, T * 1 8 Lane C: P-4 with IgA, T 0 Lane D: P-4 with IgA, T Lane E: P-1 with IgG, T 1 8 0 Lane F: P-1 with IgG, T Lane G: P-4 with IgG, T 1 8 0 Lane H: P-4 with IgG, T 1 8 * no incubation ** overnight incubation of protease fraction with substrate at 37 ° C Arrows indicate molecular weight markers, from top to bottom, respectively: 97,400 D (phosphorylase b) 43,000 D 25,700 D (ovalbumin) (^-chymotrypsin) The reaction mixtures contained 25 pi protease, 25 pi IgA or IgG (1 mg/ml water), 25 u.1 Tris hydrochloride buffer, pH 7.5 at 37 ° C , 2mM DTT. The mixtures were either immediately boiled for 5 minutes with 20 u.1 of SDSsolubilization buffer, or incubated overnight at 37 ° C followed by boiling for 5 minutes with 20 u.1 of SDS-solubilization buffer. Aliquots of 20 pi were loaded onto a 12% (wt/vol) mini-slab gel. The gel was stained with Coomassie blue dye after electrophoresis. 62 A B C E D 62a F G H Figure 12. Hydrolysis of gelatin and collagen Lane A: P-1 with gelatin, T * Lane B: P-1 with gelatin, T * by P-1 and P-4. 0 1 8 Lane C: P-1 with collagen, T 0 Lane D: P-1 with collagen, T-| Lane E: P-4 with gelatin, T Lane F: P-4 with gelatin, T 8 0 1 8 Lane G: P-4 with collagen, T 0 Lane H: P-4 with collagen, T 1 8 no incubation overnight incubation of protease fraction and substrate at 37 ° C Arrows indicate molecular weight markers, from top to bottom, respectively: 200,000 D (myosin H chain) 97,400 D (phosphorylase b) 68,000 D (bovine serum albumin) 43,000 D (ovalbumin) The reaction (1 mg/ml) mixtures contained 25 u.l protease fraction, 25 uJ gelatin or acid-soluble collagen (1 mg/ml 0.1% acetic acid), 25 u.l Tris hydrochloride buffer, pH 7.5 at 37 °C, 2 mM DTT. immediately boiled for 5 minutes The mixtures were either with 20 u,l of SDS-solubilization buffer, or incubated overnight at 37 °C followed by boiling for 5 minutes with 20 ju.l of SDS-solubilization buffer. Aliquots of 20 uJ were loaded onto a 7.5% (wt/vol) polyacrylamide resolving mini-slab gel. The gel was stained with Coomassie blue dye after electrophoresis. 63 A B C D E 63a F G H Figure Lane A: 13. H y d r o l y s i s of collagen by trypsin and P-1. boiled P-1, trypsin and collagen, To* Lane B: boiled P-1, trypsin and collagen, T18* Lane C: nonboiled P-1, trypsin and collagen, To Lane D: nonboiled P-1, trypsin and collagen, T18 Lane E: trypsin and collagen, To Lane F: trypsin and collagen, T18 * no incubation overnight incubation of P-1 and /or tryspin with substrate at 37 ° C Arrows indicate molecular weight markers, from top to bottom, respectively: 200,000 D (myosin H chain) 97,400 D (phosphorylase b) 68,000 D (bovine serum albumin) 43,000 D (ovalbumin) Reaction mixture for Lanes A-D: 25 u.l boiled or nonboiled P-1, 25 u.l acid- soluble collagen (1 mg/ml 0.1% acetic acid), 25 u.l trypsin (0.4 mg/ml water), 25 u.l Tris hydrochloride buffer (pH 7.5 at 37 °C), 2mM DTT. for Lanes E and F: Reaction mixture 25 uJ trypsin (0.4 mg/ml water), 25 u.1 acid-soluble collagen (1 mg/ml 0.1% acetic acid), 25 u.l Tris hydrochloride buffer (pH 7.5 at 37 °C), 2 mM DTT. The reactions mixtures were either boiled immediately ( T ) with 20 u.l of the SDS-solubilization buffer for 5 minutes or incubated 0 overnight ( T ) at 37 ° C followed by boiling for 5 minutes with 20 u.l of the 1 8 SDS-solubilization buffer. Aliquots of 20 u,l were loaded onto a 7.5% (wt/vol) polyacrylamide resolving mini-slab gel. The gel was stained with Coomassie blue dye after electrophoresis. 64 A B C D 64a E F Reaction with antibody No cross-reactivity to g l y c y l p r o l y l protease was found when the partially purified proteases reacted with antibody to a glycylprolyl protease. were This was determined by Western blotting as outlined in Material and Methods. It is not surprising to find a lack of cross-reactivity since the glycylprolyl protease was deemed to be pure, based upon the electrophoretic pattern produced and subsequent staining with silver which is a very sensitive method for detection of protein (Oakley et al, 1 980) 65 DISCUSSION The proteolytic activity of Bacteroides gingivalis gives this organism many potential advantages in terms of pathogenicity. A number of proteases have been characterized with regard to molecular weight, temperature and pH optima, specific inhibitors and ability to hydrolyze specific substrates. The proteases, preparation membrane P-1 and P-4, were isolated from the outer membrane (OM-1) obtained by shearing whole cells and from the outer preparation (OM-2) derived from the sonication of whole cells (Grenier & McBride, in press). Since the shearing method for removal of the outer membranes is very gentle, it is likely that little cell breakage occurred during this procedure. However, sonication is a destructive process, probably resulted in cell damage, and releasing intracellular proteins as well as the outer membranes. Grenier & McBride (in press) have described the proteolytic activity of culture supernatants, purified outer membranes, outer membrane vesicles and cell extracts of Bacteroides electrophoresis. using gingivalis BSA-polyacrylamide gel Their findings indicate that the proteolytic activity of the purified outer membranes is identical to that of the cell extracts. This activity was found to be absent from the cell extracts following ultracentrifugation which would result in the removal of the outer membrane fragments from the cell extract. The loss of proteolytic activity from the cell extract after ultracentifugation is confirmation that the proteolytic activity is associated with the outer membranes rather than with soluble proteases unique to the cell extract. The BSA-polyacrylamide gel electrophoretic procedure proved to be a rapid and very sensitive method for monitoring proteolytic activity during the purification of P-1 and P-4. Gel electrophoresis was chosen as the method of purification because it is rapid, sensitive, and reproducible. Furthermore, 66 SDS-polyacrylamide gel electrophoresis offers the ability to easily separate proteins according to their molecular weight. Separation of high molecular weight proteins is often not possible by more traditional methods because of the formation of protein aggregates. The higher molecular weight protease (P-1) was fractionable to proteolytic purity, as determined by electrophoresis conjugated to bovine serum albumin. using SDS-polyacrylamide gels The area of proteolysis was visible as a single band on the stained gel which suggests that P-1 was pure in terms of its proteolytic activity. Three narrow bands, corresponding to molecular weights of 235 kD, 220 kD and 200 kD, were visible following S D S - P A G E of nonboiled P-1 and subsequent silver staining for protein. Several bands were visible following electrophoresis and silver staining of boiled P-1 (68-18 kD). These bands may be due to denaturation of the protease after boiling with SDS-solubilization buffer. possible that at 37 ° C , in the presence of SDS, molecules migrate as one band. It is the protease and associated However, during incubation at 100 ° C , in the presence of SDS, the associated molecules may separate from the protease and each migrate as a separate band. The outer membrane is associated with insoluble hydrophobic molecules, protein and lipopolysaccharide. It is very likely that some of these molecules remain associated with the protease following purification procedures. The position of P-1 protelytic activity visible on a BSA-polyacrylamide gel (corresponding to 200 kD) correlated well with the position of the three bands seen on a silver stained gel after electrophoresis of nonboiled P-1 kD). (235-200 The presence of three bands visible after silver staining may simply reflect the conformation of the protease, as suggested by Heukeshoven & Dernick (1985) and is not an indication that each band has individual activity. proteolytic The results of the study by Heukeshoven & Dernick (1985) indicated 67 that differences in staining occurred when the protein three-dimensional structure was changed by treatment with detergents, e.g. SDS. three-dimensional Furthermore, the protein structure, and therefore the presentation of the reactive moiety in space, appeared to be the single most important factor in stainability. The appearance of a single band of proteolytic activity on the BSA- polyacrylamide gel would tend to support this, and is additional proteolytic and protein purity of P-1. evidence of the Furthermore, the appearance of a single major band, corresponding to 68 kD, after electrophoresis of boiled P-1 is another indication that the three bands represent a single protease. P-4, fractionnated to proteolytic purity (as above for P-1), in its active (nonboiled) form, had a molecular weight corresponding to 74 kD whereas the boiled protease produced two major bands after S D S - P A G E corresponding to 68 and 50 kD. It may be that these two bands again represent molecules associated with the nonboiled protease and are produced as the protease during treatment a result of the denaturation of with SDS-solubilization buffer at 100 °C. Alternatively, the bands could be the result of a conformational change in the protease following denaturation of the protease by boiling with SDS- solubilization buffer. The position of proteolytic activity (74 kD) on the BSA- polyacrylamide correlates gel very well with the single major band corresponding to 74 kD, visualized by silver staining after S D S - P A G E of nonboiled P-4, and is an indication of a high degree of proteolytic and protein purity of the P-4 protease. Lipopolysaccharide was not found in either P-1 or P-4, after S D S - P A G E and silver staining for lipopolysaccharide (results not shown). Although the proteases had different molecular weights, they were identical in their activity. The lower molecular weight protease (P-4) appeared to be more reactive than the higher molecular weight protease (P-1). The proteases were identical in their requirement for reducing agent for activity and in pH and temperature optima. The small difference in heat stability between P-1 and P-4 68 may be due to a protein complex which stabilizes P-1, making it less susceptible to changes in temperature. The proteases were identical in their activity against synthetic peptides and protein substrates. Both proteases were especially active against synthetic peptides containing arginine which, on the basis of this substrate specificity, suggests that the proteases inhibition are trypsin-like resulted rather than chymotrypsin-like, from the specific chymotrypsin even inhibitor, T P C K . though It is interesting that although the glycylprolyl dipeptide was slowly hydrolyzed, both denatured collagen and gelatin were readily degraded. the collagenolytic appears activity of the higher molecular Further investigation of weight warranted, based upon the potential ability of protease (P-1) P-1 to degrade acid- soluble collagen at 37 ° C . Both proteases completely degraded IgG and IgA. terms of virulence, This ability is important in giving the organism the potential to interfere with the host defense system and thus enhance its own survival. Previous studies (Mortensen & Kilian, 1984; Sato et al, 1987; Sunqvist et al, 1985) have reported similar results. The inhibition studies indicated that both P-1 and P-4 are serine proteases. Inhibition was produced by several serine protease inhibitors, including those active against both trypsin- (PMSF and TLCK) and chymotrypsin-like enzymes (TPCK). In addition, the sensitivity of these proteases to thiol inhibitors (PCMB, Hg and Zn ions) suggests that these groups are present at the active site. These findings are similar to those of other investigations describing trypsinlike proteases of B. gingivalis Sorsa et al, 1987; EDTA (Fujimura & Nakamura, 1987; Yoshimura et al, 1984). Ono et al, 1987; The enhancement of activity from and aprotinin may be the result of chelation of an inhibitory cation associated with the proteases. Supportive evidence is the increase in activity when cations, C a and Mg, are added to the reaction mixture. 69 The immunoreactivity studies indicate that the glycylprolyl protease purified from outer membranes of B. gingivalis different from the proteases 33277 (Grenier and McBride,1987) is purified in this work. The specificity of the antibody to the glycylprolyl protease was reinforced by the fact that only the band representing the M r of the glycylprolyl protease (29,000 D) was detected when the antibody was reacted with crude preparations of outer membrane, cell extract and with the outer membrane vesicle preparation, as outlined in Materials and Methods. Whether these fractions represent a single protease or two different proteases is not entirely clear from this investigation, since in all characteristics molecular weight, the proteases were identical. except The initial detection of three proteolytic bands on the skim milk zymogram could represent three different proteases or a single protease having three proteolytically active moieties. Further work using immunological and genetic techniques may be able to resolve this. Preparation of specific antibody to each of the purified proteases, and investigation of any cross-reactivity, should determine whether these are unique proteases or part of single large protein. Furthermore, isolation and purification of the intermediate protease seen on the zymogram would likely provide more information concerning this group of proteases. It is quite likely, based upon the findings of this investigation, that the three bands apparent on the initial zymogram represent different forms of a single protease. Evidence for this conclusion is the appearance of the major band corresponding to 68 kD which is common to both P-1 and P-4 following electrophoresis of boiled P-1 and boiled P-4. The trypsin-like protease described by Fujimura and Nakamura (1987) was also isolated from a cell extract of sonicated cells of B. gingivalis. However, their protease, soluble in Triton X-100, was found to be active at neutral pH (pH 7.5) and had a lower molecular weight by S D S - P A G E (65 kD) than either the P1 or P-4 protease in this study. The earlier investigation of Fujimura and 70 Nakamura (1981) revealed the presence of two proteases, probably membranefree, which were also inhibited by thiol inhibitors; however, no molecular weights were determined. Yoshimura et al (1984) and Ono et al (1987) described trypsin-like proteases with similar activities to the P-1 and P-4 proteases, however, the proteases were isolated from different crude fractions in each of these investigations. The protease isolated by Yoshimura et al (1984) could have been associated with either the inner or the outer membrane of the cell whereas Ono et al (1987) used culture supernatant as a starting material. Yoshimura et al (1984) did not determine the molecular weight of the partially purified protease whereas the M r of the protease purified by Ono et al (1987) was determined to be 49 kD by S D S - P A G E . Differences other than M exist among the proteases found in these r two investigations and the proteases purified in this study. The maximum activity of the protease was determined to be at pH 7.6 (Ono et al, 1987), however, information regarding pH optimum is not given by Yoshimura et al (1984). In contrast, both P-1 and P-4 had their optimum activity between the pH values between 6.0 and 6.5. Furthermore, P-1 and P-4 appear to be associated only with the outer membrane of the cell. The trypsin-like protease isolated from culture supernatant by Sorsa et al (1987) appeared similar to P-1 and P-4 in activity. The given for their protease was 35 kD (by gel filtration). molecular weight Therefore, it is not possible to make a direct comparison to the proteases isolated in this study. Activity similar to that found for P-1 and P-4 was apparent in extracellular vesicles (Grenier & Mayrand, 1987). The vesicle fraction was found to degrade azocoll and to possess trypsin-like activity, evidenced by the hydrolysis of BAPNA. The vesicles were also active against collagen. Furthermore, the polypeptide pattern (by SDS-PAGE) of the vesicle preparation was found to be similar, although not identical to that of an outer membrane fraction. It is reasonable to postulate that the proteases associated with the outer membrane 71 per se are also associated with the outer membrane vesicles. Thus both P-1 and P-4 may be bound to the vesicles and able to exert their effect within the host at some distance from the cell itself. Although it is generally recognized that B. gingivalis is involved in the pathogenesis of a number of periodontal diseases, the specific role of the proteases associated with this organism is not entirely understood. Certainly all of the information available concerning the proteolytic activity of B. gingivalis indicates an extensive and varied ability of the organism to cause destruction to the host tissues by both direct and indirect means. As such, further understanding of the characteristics of this virulent organism can only assist in the understanding and treatment of periodontal disease. 72 BIBLIOGRAPHY 1. M. Hayakawa, S. Murai and H. Takiguchi. Abiko, Y., Glycylprolyl Dent. 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Isolation of two trypsin-like proteases associated with the outer membranes of Bacteroides gingivalis Scott, Helen G. 1988
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