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Outer membrane protein OprF of P. aeruginosa Rawling, Eileen Grace

Abstract

An OprF-deficient mutant of P. aeruginosa strain M-2 was constructed by Ω mutagenesis. This strain was unable to grow in low osmolarity media and was 70% the length of the parental strain. These results confirmed that these phenotypes were not strain specific. Consistent with the appearance of OprF-deficient strains in clinical situations, an OprF-deficient strain was shown to not have a major growth disadvantage in an in vivo chamber model. Plasmids encoding truncated and cysteine-to-serine mutants of OprF were constructed by linker-insertion mutagenesis, PCR and subcloning of a previously characterized mutant. Analysis of the resulting proteins indicated that between 102 and 163 N-terminal amino acids of OprF was required for protein expression as determined by Western immunoblotting. All of the truncated mutants expressed were associated with the outer membrane, indicating that the N-terminal 163 amino acids of OprF were sufficient for this association. None of the truncated-OprF mutants tested were associated with the peptidoglycan, indicating that more than 215 N-terminal amino acids of OprF are required for this association. Strains that encoded at least two cysteines were 2-mercaptoethanol modifiable. The full-length cloned OprF and the truncated mutant expressing the N-terminal 290 amino acids were normally heat modifiable. When denatured prior to electrophoresis, the remaining truncated mutants had apparent molecular weights lower than those of untreated samples indicating that between 215 and 290 amino acids were required for the protein to be normally heat modified. Although the truncated-OprF mutants were able to grow in low osmolarity media and were significantly longer than the OprF-deficient strain, the C-terminal half of OprF appeared to be required for the wild-type growth and length. The cysteine-to-serine OprF mutants were associated with the outer membrane and were heat modifiable. Analysis of these mutants with and without 2-mercaptoethanol was consistent with the hypothesis that wild-type OprF has two disulphide bonds Monoclonal antibody reactivity with overlapping octapeptides equivalent to the primary sequence of OprF localized three epitopes. Indirect immunofluorescence and opsonic phagocytosis studies identified the surface location of epitopes binding nine OprF-specific monoclonal antibodies. This information was incorporated into an updated secondary structure model of OprF.

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