Buts Lieven, Bouckaert Julie, De Genst Erwin, Loris Remy, Oscarson Stefan, Lahmann Martina, Messens Joris, Brosens Elke, Wyns Lode, De Greve Henri
Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie, Brussels, Belgium.
Mol Microbiol. 2003 Aug;49(3):705-15. doi: 10.1046/j.1365-2958.2003.03600.x.
The F17-G adhesin at the tip of flexible F17 fimbriae of enterotoxigenic Escherichia coli mediates binding to N-acetyl-beta-D-glucosamine-presenting receptors on the microvilli of the intestinal epithelium of ruminants. We report the 1.7 A resolution crystal structure of the lectin domain of F17-G, both free and in complex with N-acetylglucosamine. The monosaccharide is bound on the side of the ellipsoid-shaped protein in a conserved site around which all natural variations of F17-G are clustered. A model is proposed for the interaction between F17-fimbriated E. coli and microvilli with enhanced affinity compared with the binding constant we determined for F17-G binding to N-acetylglucosamine (0.85 mM-1). Unexpectedly, the F17-G structure reveals that the lectin domains of the F17-G, PapGII and FimH fimbrial adhesins all share the immunoglobulin-like fold of the structural components (pilins) of their fimbriae, despite lack of any sequence identity. Fold comparisons with pilin and chaperone structures of the chaperone/usher pathway highlight the central role of the C-terminal beta-strand G of the immunoglobulin-like fold and provides new insights into pilus assembly, function and adhesion.
产肠毒素大肠杆菌柔性F17菌毛尖端的F17-G黏附素介导与反刍动物肠上皮微绒毛上呈现N-乙酰-β-D-葡萄糖胺的受体结合。我们报道了F17-G凝集素结构域的1.7埃分辨率晶体结构，包括其游离形式以及与N-乙酰葡糖胺结合的复合物形式。单糖结合在椭圆形蛋白质的一侧，位于一个保守位点，F17-G的所有天然变异都聚集在该位点周围。我们提出了一个F17菌毛化大肠杆菌与微绒毛之间相互作用的模型，与我们测定的F17-G与N-乙酰葡糖胺结合常数（0.85 mM-1）相比，其亲和力有所增强。出乎意料的是，F17-G结构显示，F17-G、PapGII和FimH菌毛黏附素的凝集素结构域都具有与其菌毛结构成分（菌毛蛋白）相似的免疫球蛋白样折叠，尽管它们之间没有任何序列同一性。与伴侣/组装途径的菌毛蛋白和伴侣结构进行折叠比较，突出了免疫球蛋白样折叠的C端β链G的核心作用，并为菌毛组装、功能和黏附提供了新的见解。
