The function of OmpA in Escherichia coli.

Outer membrane protein A (OmpA) is a major protein in the Escherichia coli outer membrane. In this study, the function of OmpA in E. coli stress survival was examined. An E. coli K1 ompA-deletion mutant was significantly more sensitive than that of its parent strain to sodium dodecyl sulfate (SDS), cholate, acidic environment, high osmolarity, and pooled human serum. A number of amino acid changes at the extracellular loops of OmpA did not affect the viability of E. coli, while short peptide insertions in the periplasmic turns of the OmpA beta-barrel decreased E. coli resistance to environmental stresses. Moreover, ompA mutants were found to survive much better within brain microvascular endothelial cells than the wild-type strain, supporting that OmpA is a major target in mammalian host cell defense. These results indicated that OmpA plays a vital structural role in E. coli, and suggested that a perfect beta-barrel structure of OmpA is important for outer membrane stability. Based on these results and the published OmpA structural analyses, I propose that OmpA is composed of three functional domains including a hydrophilic extracellular mass, a beta-barrel transmembrane structure, and a peptidoglycan binding domain.