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Cloning and characterization of the oprF gene for protein F from Pseudomonas aeruginosa Woodruff, Wendy Anne


The oprF gene encoding porin protein F from Pseudomonas aeruginosa was cloned onto a cosmid vector into Escherichia coli. Protein F was expressed in large amounts in E. coli and retained its heat- and reduction-modifiable and immunological characteristics. The cloned oprF gene product was purified from E. coli and characterized with respect to pore-forming ability in black lipid bilayers. Small channels, with an average single channel conductance of approximately 0.4 nS, were observed. A similar small channel size was observed for native protein F. The oprF sequences were used as a DNA-DNA hybridization probe with chromosomal DNA from the 17 IATS (International Antigen Typing Scheme) strains of P. aeruginosa, 52 clinical isolates and the non-aeruginosa Pseudomonads. Conservation of oprF sequences was observed among all the P. aeruginosa strains and to a lesser extent among the non-aeruginosa strains of the P. fluorescens rRNA homology group. Insertion mutations in the oprF gene were created in vivo by Tn1mutagenesis of the cloned gene in E. coli and in vitro by insertion of the streptomycin-encoding Ω fragment into the cloned gene, followed by transfer of the mutated protein F gene back into P. aeruginosa and homologous recombination with the chromosome. The oprF mutants were characterized by gel electrophoresis and immunoblotting, and it was shown that the mutants had lost protein F. The P. aeruginosa oprF mutants were characterized with respect to growth rates, antibiotic permeability and cell surface hydrophobicity. The results of these studies indicated that major alterations in the cell surface had occurred and that the cells were unable to grow in a non-defined liquid medium without added electrolytes. Marginal differences were observed in MICs (minimum inhibitory concentrations) of hydrophilic antibiotics for the oprF mutants compared with their protein F-sufficient parents. The putative roles of protein F in antibiotic permeability and general outer membrane permeability are discussed. Evidence for extensive homologies between protein F, the OmpA protein of E. coli and PHIII of Neisseria gonorrhoeae are presented. A role for protein F in prophylactic anti-Pseudomonas therapy, as a target for vaccine development, is proposed.

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