The DraC usher in Dr fimbriae biogenesis of uropathogenic E. coli Dr+ strains

Biogenesis of Dr fimbriae encoded by the dra gene cluster of uropathogenic Escherichia coli strains requires the chaperone-usher pathway. This secretion system is based on two non-structural assembly components, the DraB periplasmic chaperone and DraC outer-membrane usher. The DraB controls the folding of DraE subunits, and DraC forms the assembly and secretion platform for polymerization of subunits in linear fibers. In this study, mutagenesis of the DraC N-terminus was undertaken to select residues critical for Dr fimbriae bioassembly. The DraC-F4A, DraC-C64, DraC-C100A and DraC-W142A significantly reduced the adhesive ability of E. coli strains. The biological activity of the DraC mutants as a assembly platform for Dr fimbriae polymerization was verified by agglutination of human erythrocytes and adhesion to DAF localized at the surface of CHO-DAF+ and HeLa cells. The residue F4 of the DraC usher conserved among FGL and FGS chaperone-assembled adhesive organelles can be used to design pillicides blocking the biogenesis of Dr fimbriae. Because the draC and afaC-III genes share 100% identity the range of the virulence determinant inhibitors could also be extended to E. coli strains encoding afa-3 gene cluster. The investigations performed showed that the usher N-terminus plays an important role in biogenesis of complete fiber.