TYPE-1 FIMBRIAL SHAFTS OF ESCHERICHIA-COLI AND KLEBSIELLA-PNEUMONIAE INFLUENCE SUGAR-BINDING SPECIFICITIES OF THEIR FIMH ADHESINS

The type 1 fimbriae of enterobacteria comprise FimA, which constitutes most of the fimbrial shaft, and a cassette of three minor ancillary s ubunits including FimH, the mannose-binding moiety. The sugar-binding specificities of Escherichia coli and Klebsiella pneumoniae type 1 fim briae were examined by determining the relative activities of two arom atic mannosides in inhibiting the yeast aggregation caused by the fimb riated bacteria. 4-Methylumbelliferyl alpha-mannoside (MeUmb alpha Man ) was approximately 10-fold more effective than p-nitrophenyl alpha-ma nnoside (p-NP alpha Man) in inhibiting the yeast aggregation caused by the recombinant expressing native E. coli type 1 fimbriae. In contras t, MeUmb alpha Man was only fourfold more effective than p-NP alpha Ma n in assays employing the recombinant expressing native K. pneumoniae type 1 fimbriae. In order to elucidate the molecular mechanisms underl ying the sugar-binding specificities of type 1 fimbriae in the two spe cies, transcomplementation studies were performed and resulted in the creation of recombinants expressing two types of hybrid fimbriae: one consisting of a cassette of minor subunits off. call fimbriae borne on a filamentous shaft of K. pneumoniae FimA subunits and the other cons isting of a cassette of K. pneumoniae minor fimbrial subunits borne on a shaft off. coli FimA subunits. Although the heterologous FimH was i ncorporated into the fimbrial filaments in amounts comparable to those observed in native fimbriae, the hemagglutination activities of recom binants expressing hybrid fimbriae were significantly lower than those of their counterparts bearing native fimbriae. The sugar-binding spec ificity of the recombinant expressing hybrid fimbriae consisting of an E. coli shaft bearing K. pneumoniae FimH was different from those of recombinants expressing native K. pneumoniae fimbriae in its affinity for the two aromatic sugars but was remarkably similar to the specific ities exhibited by recombinants expressing native E. coli fimbriae. Co nversely, the sugar-binding specificity of the recombinant expressing hybrid fimbriae consisting of a K. pneumoniae shaft bearing E. coli Fi mH was different from that of the recombinant expressing native E. col i fimbriae but was very similar to those of recombinants expressing na tive K. pneumoniae fimbriae. We conclude that the differences in the s ugar-binding specificity between E. coli and K. pneumoniae FimH fimbri al subunits is influenced by the fimbrial shafts which carry the adhes in molecules in a functionally competent form at the distal tips.