Madison B, Ofek I, Clegg S, Abraham S N
Department of Clinical Laboratory Sciences, University of Tennessee, Memphis 68318.
Infect Immun. 1994 Mar;62(3):843-8. doi: 10.1128/iai.62.3.843-848.1994.
The type 1 fimbriae of enterobacteria comprise FimA, which constitutes most of the fimbrial shaft, and a cassette of three minor ancillary subunits including FimH, the mannose-binding moiety. The sugar-binding specificities of Escherichia coli and Klebsiella pneumoniae type 1 fimbriae were examined by determining the relative activities of two aromatic mannosides in inhibiting the yeast aggregation caused by the fimbriated bacteria. 4-Methylumbelliferyl alpha-mannoside (MeUmb alpha Man) was approximately 10-fold more effective than p-nitrophenyl alpha-mannoside (p-NP alpha Man) in inhibiting the yeast aggregation caused by the recombinant expressing native E. coli type 1 fimbriae. In contrast, MeUmb alpha Man was only fourfold more effective than p-NP alpha Man in assays employing the recombinant expressing native K. pneumoniae type 1 fimbriae. In order to elucidate the molecular mechanisms underlying the sugar-binding specificities of type 1 fimbriae in the two species, 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 of E. coli fimbriae borne on a filamentous shaft of K. pneumoniae FimA subunits and the other consisting of a cassette of K. pneumoniae minor fimbrial subunits borne on a shaft of E. coli FimA subunits. Although the heterologous FimH was incorporated into the fimbrial filaments in amounts comparable to those observed in native fimbriae, the hemagglutination activities of recombinants expressing hybrid fimbriae were significantly lower than those of their counterparts bearing native fimbriae. The sugar-binding specificity 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 specificities exhibited by recombinants expressing native E. coli fimbriae. Conversely, the sugar-binding specificity of the recombinant expressing hybrid fimbriae consisting of a K. pneumoniae shaft bearing E. coli FimH was different from that of the recombinant expressing native E. coli fimbriae but was very similar to those of recombinants expressing native K. pneumoniae fimbriae. We conclude that the differences in the sugar-binding specificity between E. coli and K. pneumoniae FimH fimbrial subunits is influenced by the fimbrial shafts which carry the adhesin molecules in a functionally competent form at the distal tips.
肠道杆菌的1型菌毛由构成菌毛杆大部分的FimA以及包括甘露糖结合部分FimH在内的三个次要辅助亚基组成的一个操纵子组成。通过测定两种芳香族甘露糖苷在抑制由菌毛化细菌引起的酵母聚集方面的相对活性，研究了大肠杆菌和肺炎克雷伯菌1型菌毛的糖结合特异性。在抑制由表达天然大肠杆菌1型菌毛的重组体引起的酵母聚集方面，4-甲基伞形酮α-D-甘露糖苷（MeUmbαMan）的效力比对硝基苯基α-D-甘露糖苷（p-NPαMan）高约10倍。相比之下，在使用表达天然肺炎克雷伯菌1型菌毛的重组体的试验中，MeUmbαMan的效力仅比对硝基苯基α-D-甘露糖苷高4倍。为了阐明这两个物种中1型菌毛糖结合特异性的分子机制，进行了转互补研究，结果产生了表达两种杂交菌毛的重组体：一种由肺炎克雷伯菌FimA亚基的丝状杆携带的大肠杆菌菌毛次要亚基操纵子组成，另一种由大肠杆菌FimA亚基的杆携带的肺炎克雷伯菌次要菌毛亚基操纵子组成。尽管异源FimH以与天然菌毛中观察到的量相当的量掺入菌毛丝中，但表达杂交菌毛的重组体的血凝活性明显低于携带天然菌毛的对应重组体。由携带肺炎克雷伯菌FimH的大肠杆菌杆组成的表达杂交菌毛的重组体对两种芳香糖的亲和力与表达天然肺炎克雷伯菌菌毛的重组体不同，但其与表达天然大肠杆菌菌毛的重组体表现出的特异性非常相似。相反，由携带大肠杆菌FimH的肺炎克雷伯菌杆组成的表达杂交菌毛的重组体的糖结合特异性与表达天然大肠杆菌菌毛的重组体不同，但与表达天然肺炎克雷伯菌菌毛的重组体非常相似。我们得出结论，大肠杆菌和肺炎克雷伯菌FimH菌毛亚基之间糖结合特异性的差异受菌毛杆的影响，菌毛杆以功能上有效的形式在远端携带粘附分子。
