Escherichia coli K-12 outer membrane protein (OmpA) as a bacteriophage receptor: Analysis of mutant genes expressing altered protein

Abstract

The outer membrane protein OmpA of Escherichia coli K-12 serves as a receptor for a number of T-even-like phages. We have isolated a series of ompA mutants which are resistant to such phages but which still produce the OmpA protein. None of the mutants was able to either irreversibly or reversibly bind the phage with which they had been selected. Also, the OmpA protein is required for the action of colicins K and L and for the stabilization of mating aggregates in conjugation. Conjugal proficiency was unaltered in all cases. Various degrees of colicin resistance was found; however, the resistance pattern did not correlate with the phage resistance pattern. DNA sequence analyses revealed that, in the mutants, the 325-residue OmpA protein had suffered the following alterations: Gly-65→Asp, Gly-65→Arg, Glu-68→Gly, Glu-68→Lys (two isolates), Gly-70→Asp (four isolates), Gly-70→Val, Ala-Asp-Thr-Lys-107→Ala-Lys (caused by a 6-base-pair deletion), Val-110→Asp, and Gly-154→Ser. These mutants exhibited a complex pattern of resistance-sensitivity to 14 different OmpA-specific phages, suggesting that they recognize different areas of the protein. In addition to the three clusters of mutational alterations around residues 68, 110, and 154, a site around residue 25 has been predicted to be involved in conjugation and in binding of a phage and a bacteriocin. These four areas are regularly spaced, being about 40 residues apart from each other. A model is suggested in which the OmpA polypeptide repeatedly traverses the outer membrane in cross-β structure, exposing the four areas to the outside.