Pseudomonas aeruginosa outer membrane protein F: structural role and relationship to the Escherichia coli OmpA protein

A Pseudomonas aeruginosa outer membrane protein F-deficient omega-insertion mutant strain H636, in contrast to its protein F-sufficient parent strain H103, was unable to grow on unsupplemented Proteose Peptone no. 2 broth (Difco Laboratories, Detroit, Mich.). Addition of high concentrations of NaCl, KCl, glucose, sucrose, or potassium succinate permitted growth of strain H636 at rates approaching those of the parent strain H103. Strain H636 cells were 33% shorter and had a 46% smaller cross-sectional area than did the parent strain growing at similar rates on the same medium. These properties of the oprF::omega mutant were analogous to those previously observed for Escherichia coli ompA mutants in an lpp (Braun lipoprotein-deficient) mutant background. Therefore, we compared P. aeruginosa protein F and the E. coli OmpA protein. In addition to many similarities previously described, sequence alignment demonstrated substantial amino acid sequence homology throughout the carboxy-terminal 168 to 180 amino acids of the two proteins. Consistent with this observation, polyclonal antiserum specific for OmpA reacted on Western blots (immunoblots) with protein F. Expression of protein F from the cloned oprF gene in an E. coli ompA lpp double mutant resulted in a 1.7-fold increase in cell length and a 2.1-fold increase in cross-sectional area compared with values for the same mutant containing only the plasmid vector onto which the oprF gene had been cloned. These results favor a structural role for P. aeruginosa protein F and suggest that it is strongly related to the E. coli OmpA protein.