Functional analysis of the minor subunits of S fimbrial adhesin (Sfal) in pathogenic Escherichia coli

S fimbrial adhesins I and II (SfaI and II), produced by extraintestinal Esc herichia coli pathogens that cause urinary tract infections (UTI) and newbo rn meningitis (NBM), respectively, mediate bacterial adherence to sialic ac id-containing glycoprotein receptors present on host epithelial cells and e xtracellular matrix. The S fimbrial adhesin complexes consist of four prote ins: SfaI-A, the major subunit protein and the minor subunit proteins SfaI- G, SfaI-S and SfaI-H. Sialic acid-specific binding is mediated by the minor subunit protein SfaI-S. In order to determine whether the minor subunit pr oteins SfaI-G, -S and -H play a role in the modulation of adherence and the degree of fimbriation, a transcomplementation system was developed. A non- adhesive E. coli K-12 derivative, harbouring the sfaI-A gene but lacking sf aI-G, -S and -H, was transformed with sfaI-G, -S or -H. Only SfaI-S was abl e to increase the degree of fimbriation and to confer adhesion properties o n the recombinant E. coli K-12 strains. Amino acid residues in SfaI-S that are involved in modulation of fimbriation as well as in receptor recognitio n were localized by random and site-directed mutagenesis.