FIMH FAMILY OF TYPE-1 FIMBRIAL ADHESINS - FUNCTIONAL-HETEROGENEITY DUE TO MINOR SEQUENCE VARIATIONS AMONG FIMH GENES

We recently reported that the type l-fimbriated Escherichia coli strai ns CSH-50 and HB101(pPKL4), both K-12 derivatives, have different patt erns of adhesion to yeast mannan, human plasma fibronectin, and fibron ectin derivatives, suggesting functional heterogeneity of type 1 fimbr iae. In this report, we provide evidence that this functional heteroge neity is due to variations in the fimH genes. We also investigated fun ctional heterogeneity among clinical isolates and whether variation in fimH genes accounts for differences in receptor specificity. Twelve i solates obtained from human urine were tested for their ability to adh ere to mannan, fibronectin, periodate-treated fibronectin, and a synth etic peptide copying the 30 amino-terminal residues of fibronectin. CS H-50 and HB101(pPKL4) were tested for comparison. Selected isolates we re also tested for adhesion to purified fragments spanning the entire fibronectin molecule. Three distinct functional classes, designated M, MF, and MFP, were observed. The fimH genes were amplified by PCR from chromosomal DNA obtained from representative strains and expressed in a Delta fim strain (AAEC191A) transformed with a recombinant plasmid containing the entire fim gene cluster but with a translational stop-l inker inserted into the fimH gene (pPKL114). Cloned fimH genes conferr ed on AAEC191A(pPKL114) receptor specificities mimicking those of the parent strains from which the fimH genes were obtained, demonstrating that the FimH subunits are responsible for the functional heterogeneit y. Representative fimH genes were sequenced, and the deduced amino aci d sequences were compared with the previously published FimH sequence. Allelic variants exhibiting >98% homology and encoding proteins diffe ring by as little as a single amino acid substitution confer distinct adhesive phenotypes. This unexpected adhesive diversity within the Fim H family broadens the scope of potential receptors for enterobacterial adhesion and may lead to a fundamental change in our understanding of the role(s) that type 1 fimbriae may play in enterobacterial ecology or pathogenesis.