The flagellar stator unit is an oligomeric complex of two membrane proteins (MotA₅B₂) that powers bi-directional rotation of the bacterial flagellum. Harnessing the ion motive force across the cytoplasmic membrane, the stator unit operates as a miniature rotary motor itself to provide torque for rotation of the flagellum. Recent cryo-electron microscopic (cryo-EM) structures of the stator unit provided novel insights into its assembly, function, and subunit stoichiometry, revealing the ion flux pathway and the torque generation mechanism. Furthermore, in situ cryo-electron tomography (cryo-ET) studies revealed unprecedented details of the interactions between stator unit and rotor. In this review, we summarize recent advances in our understanding of the structure and function of the flagellar stator unit, torque generation, and directional switching of the motor.

鞭毛定子单元是两种膜蛋白 (MotA ₅ B ₂ ) 的寡聚复合物，它为细菌鞭毛的双向旋转提供动力。利用穿过细胞质膜的离子动力，定子单元本身作为一个微型旋转电机运行，为鞭毛的旋转提供扭矩。最近定子单元的低温电子显微镜 (cryo-EM) 结构为其组装、功能和亚基化学计量提供了新的见解，揭示了离子通量路径和扭矩产生机制。此外，现场低温电子断层扫描 (cryo-ET) 研究揭示了定子单元和转子之间相互作用的前所未有的细节。在这篇综述中，我们总结了我们对鞭毛定子单元的结构和功能、扭矩产生和电机方向切换的理解方面的最新进展。