Bachmann Paul, Afanasyev Pavel, Boehringer Daniel, Glockshuber Rudi
Institute of Molecular Biology and Biophysics, ETH Zürich, Otto-Stern-Weg 5, Zürich, 8093, Switzerland.
Cryo-EM Knowledge Hub (CEMK), ETH Zürich, Otto-Stern-Weg 3, Zürich, 8093, Switzerland.
Nat Commun. 2025 May 29;16(1):4988. doi: 10.1038/s41467-025-60325-z.
Uropathogenic Escherichia coli strains use filamentous type 1 pili to adhere to and invade uroepithelial cells. The pilus consists of a flexible tip fibrillum, formed by the adhesin FimH and the subunits FimG and FimF. The pilus rod is a helical assembly of up to 3000 copies of the main subunit FimA, terminated by a single copy of the subunit FimI that anchors the rod to the assembly platform FimD in the outer membrane. Although type 1 pilus assembly can be completely reconstituted in vitro, the precise mechanism of assembly termination on FimD is still unknown. Here, we present cryo-electron microscopy structures of the fully assembled pilus with all its components prior to and after incorporation of FimI, capped with the assembly chaperone FimC. The structures reveal that FimD positions the proximal end of the pilus rod at an angle of ca. 50 degrees relative to the plane of the outer membrane. Specific interactions between FimI and FimC, absent in the equivalent FimA-FimC interface of the non-terminated pilus, stabilize the assembly-terminated state. In addition, we present structures of the transition region between the tip fibrillum and the helical rod, showing how FimF aligns the tip fibrillum along the rod axis.
尿路致病性大肠杆菌菌株利用1型菌毛粘附并侵入尿道上皮细胞。菌毛由柔性的尖端纤丝组成，该纤丝由粘附素FimH以及亚基FimG和FimF形成。菌毛杆是由多达3000个主要亚基FimA组成的螺旋组装体，由单个亚基FimI终止，该亚基将菌毛杆锚定在外膜中的组装平台FimD上。尽管1型菌毛组装可以在体外完全重建，但FimD上组装终止的确切机制仍然未知。在这里，我们展示了完全组装好的菌毛在结合FimI之前和之后的冷冻电子显微镜结构，其顶端带有组装伴侣蛋白FimC。这些结构表明，FimD将菌毛杆的近端定位在相对于外膜平面约50度的角度。在未终止的菌毛的等效FimA - FimC界面中不存在的FimI和FimC之间的特定相互作用，稳定了组装终止状态。此外，我们展示了尖端纤丝和螺旋杆之间过渡区域的结构，显示了FimF如何使尖端纤丝沿杆轴排列。
