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Structural studies on Klebsiella capsular polysaccharides Mackie, Keith L.

Abstract

Eighty-one serologically distinct strains of Klebsiella bacteria are known. The capsular polysaccharides from these bacteria are their antigenic determinants and in order to help understand the chemical basis of serological differentiation, the detailed chemical structures of these polysaccharides are being determined. The capsular polysaccharides isolated from Klebsiella serotypes K32, K36 and K70 are presented here and have been established using many different chemical techniques. Methyla- tion, partial hydrolysis, periodate oxidation and 3-elimination procedures have yielded analysable subunits of the polysaccharides Extensive use has been made of n.m.r. spectroscopy (¹H and 13 C), mass spectrometry, gas-liquid chromatography and gel filtration in the isolation and identification of the products obtained from the various degradative techniques. The repeating unit structures of K32, K36 and K70 are shown to be as follows: [chemical structures]. Some features of special interest in these structures include: the extreme acid lability of the pyruvate acetal when linking hydroxyls on C₃ and C₄ of a 2-linked L-rharanose residue (K32, K70); the existence of a 3-Lj-rhamnose unit in the structure of K32; and the presence of the pyruvate acetal on only 50% of the linear, six sugar, repeating units of K70. It is also interesting to note that while K70 and K36 have almost the same quantitative composition the chemical structures are markedly different. An efficient means of isolating large quantities of single repeating units of the Klebsiella polysaccharides using glycanase enzymes borne and utilised by specific bacteriophage, is demonstrated. A bacteriophage specific for Klebsiella K32 has been propagated, purified and used to depolymerise K32 polysaccharide. Analysis of the resulting oligosaccharides has shown the glycanase enzyme to be a a-rhamnosidase which cleaves K32 as shown below. [chemical structure] The degradation via bacteriophage is a new area of research and the work described here is only preliminary and as such is presented as an appendix.

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