Center for Structural Biology, CCR, NCI, Frederick, MD, USA.
Sir William Dunn School of Pathology, University of Oxford, Oxford, UK.
Nat Microbiol. 2024 May;9(5):1282-1292. doi: 10.1038/s41564-024-01630-z. Epub 2024 Mar 8.
The bacterial flagellum is a macromolecular protein complex that harvests energy from uni-directional ion flow across the inner membrane to power bacterial swimming via rotation of the flagellar filament. Rotation is bi-directional, with binding of a cytoplasmic chemotactic response regulator controlling reversal, though the structural and mechanistic bases for rotational switching are not well understood. Here we present cryoelectron microscopy structures of intact Salmonella flagellar basal bodies (3.2-5.5 Å), including the cytoplasmic C-ring complexes required for power transmission, in both counter-clockwise and clockwise rotational conformations. These reveal 180° movements of both the N- and C-terminal domains of the FliG protein, which, when combined with a high-resolution cryoelectron microscopy structure of the MotAB stator, show that the stator shifts from the outside to the inside of the C-ring. This enables rotational switching and reveals how uni-directional ion flow across the inner membrane is used to accomplish bi-directional rotation of the flagellum.
细菌鞭毛是一种大分子蛋白复合物，它从内膜单向离子流中获取能量，通过鞭毛丝的旋转来驱动细菌游动。旋转是双向的，细胞质趋化反应调节剂的结合控制反转，尽管旋转转换的结构和机制基础还不是很清楚。在这里，我们展示了完整的沙门氏菌鞭毛基体的低温电子显微镜结构（3.2-5.5Å），包括用于动力传递的细胞质 C 环复合物，处于逆时针和顺时针旋转构象中。这些结构揭示了 FliG 蛋白的 N 端和 C 端结构域的 180°运动，当与 MotAB 定子的高分辨率低温电子显微镜结构结合时，表明定子从 C 环的外部移动到内部。这使得旋转转换成为可能，并揭示了如何利用内膜单向离子流来实现鞭毛的双向旋转。
