Pore formation by pho-controlled outer-membrane proteins of various Enterobacteriaceae in lipid bilayers

The structural genes of the PhoE porins of Klebsiella pneumonia, Enterobacter cloacae and Escherichia coli C, cloned in multicopy plasmids, were transfered into a porin-deficient E. coli K-12 strain, which was constitutive for the pho regulon, and the PhoE porins were isolated and purified. PhoE of Salmonella typhimurium could not be cloned but was isolated from a pho-constitutive strain. Reconstitution experiments with artificial lipid bilayer membranes showed that the different PhoE proteins formed pores exhibiting a single-channel conductance of about 200 pS at 0.1 M KCl. All PhoE porins formed anion-selective channels in KCl at neutral pH. The degree of the selectivity was dependent on the PhoE species. The different PhoE porins formed general diffusion pores similar to the general porins but exhibited a considerable advantage for the permeation of phosphate through the outer membrane as compared to the constitutive OmpC and OmpF porins of E. coli K-12.