Demonstration of a bacteriophage receptor site on the Escherichia coli K12 outer‐membrane protein OmpC by the use of a protease

Abstract

The Escherichia coli K12 outer-membrane proteins OmpA, OmpC, OmpF, PhoE, and LamB (all of transmembrane nature) can serve as phage receptors. We have shown previously that one OmpA-specific phage, Ox2, can give rise to the host range mutants Ox2h10 and Ox2h12, with the latter being derived from the former [Morona. R. & Henning, U. (1984) J. Bacteriol. 159, 579–582]. Unlike Ox2, both host range phages can use the OmpA and OmpC proteins as receptors and Ox2h12 is better adapted to the OmpC protein than Ox2h10. In a search for the site(s) of OmpC protein involved in phage recognition, it was found that proteinase K is able to cleave all of the proteins mentioned above. OmpC protein (M_r= 38306) could be cleaved from outside the cell by proteinase K resulting in two fragments of M_r∼ 21000 and M_r∼ 17500. The use of OmpC-PhoE hybrid proteins allowed us to assign the ∼ 21000-M_r fragment to the CO₂H-terminal moiety of the protein. Proteinase K treatment of intact cells abolished their activity to neutralize the OmpC-specific phage Tulb and reduced this ability towards phage Ox2h12. The OmpA, OmpF, PhoE and LamB proteins were cleaved by the protease not in intact cells but only when acting on cell envelopes. The sizes of the OmpC protein fragments and the results obtained with the hybrid proteins very strongly suggest that the protein is cleaved from outside the cell at a region involving amino acid residues 150–178 of the 346-residue protein, which shows homology to two regions of the OmpA protein which are involved in its phage receptor site (loc. cit.). These areas also exhibit some homology to a region of the LamB protein which is thought to be part of this protein's receptor site [Charbit et al. (1984) J. Mol. Biol. 175, 395–401]. This suggests that there is a common denominator for proteinaceous phage receptor site because the LamB-specific phage λ and phage Tulb are of completely different nature. We conclude that the region of the OmpC protein in question is cell-surface-exposed and acts as a phage receptor site.