Bouckaert Julie, Mackenzie Jenny, de Paz José L, Chipwaza Beatrice, Choudhury Devapriya, Zavialov Anton, Mannerstedt Karin, Anderson Jennifer, Piérard Denis, Wyns Lode, Seeberger Peter H, Oscarson Stefan, De Greve Henri, Knight Stefan D
Department of Ultrastructure, Vrije Universiteit Brussel, Flanders Interuniversity Institute for Biotechnology (VIB), Pleinlaan 2, 1050 Brussels, Belgium.
Mol Microbiol. 2006 Sep;61(6):1556-68. doi: 10.1111/j.1365-2958.2006.05352.x. Epub 2006 Aug 23.
Type-1 fimbriae are important virulence factors for the establishment of Escherichia coli urinary tract infections. Bacterial adhesion to the high-mannosylated uroplakin Ia glycoprotein receptors of bladder epithelium is mediated by the FimH adhesin. Previous studies have attributed differences in mannose-sensitive adhesion phenotypes between faecal and uropathogenic E. coli to sequence variation in the FimH receptor-binding domain. We find that FimH variants from uropathogenic, faecal and enterohaemorrhagic isolates express the same specificities and affinities for high-mannose structures. The only exceptions are FimHs from O157 strains that carry a mutation (Asn135Lys) in the mannose-binding pocket that abolishes all binding. A high-mannose microarray shows that all substructures are bound by FimH and that the largest oligomannose is not necessarily the best binder. Affinity measurements demonstrate a strong preference towards oligomannosides exposing Manalpha1-3Man at their non-reducing end. Binding is further enhanced by the beta1-4-linkage to GlcNAc, where binding is 100-fold better than that of alpha-d-mannose. Manalpha1-3Manbeta1-4GlcNAc, a major oligosaccharide present in the urine of alpha-mannosidosis patients, thus constitutes a well-defined FimH epitope. Differences in affinities for high-mannose structures are at least 10-fold larger than differences in numbers of adherent bacteria between faecal and uropathogenic strains. Our results imply that the carbohydrate expression profile of targeted host tissues and of natural inhibitors in urine, such as Tamm-Horsfall protein, are stronger determinants of adhesion than FimH variation.
1型菌毛是大肠杆菌引起尿路感染的重要毒力因子。细菌通过FimH黏附素与膀胱上皮细胞的高甘露糖基化尿血小板膜蛋白Ia糖蛋白受体结合。先前的研究将粪便型和尿路致病性大肠杆菌之间甘露糖敏感黏附表型的差异归因于FimH受体结合域的序列变异。我们发现，尿路致病性、粪便型和肠出血性大肠杆菌分离株的FimH变体对高甘露糖结构表现出相同的特异性和亲和力。唯一的例外是来自O157菌株的FimH，其甘露糖结合口袋中存在一个突变（Asn135Lys），该突变消除了所有结合能力。高甘露糖微阵列显示，所有亚结构均能被FimH结合，且最大的低聚甘露糖不一定是最佳结合物。亲和力测量表明，FimH对在其非还原端暴露Manα1-3Man的低聚甘露糖苷有强烈偏好。与GlcNAc的β1-4连接进一步增强了结合，其结合能力比α-D-甘露糖强100倍。Manα1-3Manβ1-4GlcNAc是α-甘露糖苷贮积症患者尿液中的一种主要寡糖，因此构成了一个明确的FimH表位。粪便型和尿路致病性菌株对高甘露糖结构的亲和力差异至少比黏附细菌数量差异大10倍。我们的结果表明，靶向宿主组织和尿液中天然抑制剂（如Tamm-Horsfall蛋白）的碳水化合物表达谱比FimH变异更能决定黏附。
