Correlation Between the Expression of an Escherichia coliCell Surface Protein and the Ability of the Protein to Bind to Lipopolysaccharide

The ompAgene of Escherichia colicodes for a major protein of the outer membrane. When this gene was moved between various unrelated strains (E. coliK-12 and two clinical isolates of E. coli) by transduction, the gene was expressed very poorly. Recombinants carrying “foreign” genes produced no OmpA protein which could be detected on polyacrylamide gels and became resistant to bacteriophage K3, which uses this protein as receptor. The recombinants were sensitive to host-range mutants of K3, indicating a very low level of OmpA protein was produced. When an E. coliK-12 recombinant carrying an unexpressed foreign ompAallele was subjected to two cycles of selection for an OmpA+phenotype, a mutant strain was obtained which was sensitive to K3 and which expressed nearly normal levels of OmpA protein in the outer membrane. This strain carried mutations in the foreign ompAgene, as indicated both by genetic mapping and the alteration of a peptide in the mutant OmpA protein. The ability of the OmpA protein to bind to lipopolysaccharide (LPS) showed similar strain specificity, and the mutant OmpA protein which was expressed in an unrelated host showed enhanced ability to bind LPS from its new host. Thus, cell surface expression of the ompAgene appears to depend upon the ability of the gene product to bind LPS, suggesting that an interaction between the protein and LPS plays an essential role in biosynthesis of this outer membrane protein.