“Structural Basis of Assembly and Torque Transmission of the Bacterial Flagellar Motor”, Jiaxing Tan, Xing Zhang, Xiaofei Wang, Caihuang Xu, Shenghai Chang, Hangjun Wu, Ting Wang, Huihui Liang, Haichun Gao, Yan Zhou, Yongqun Zhu2021-04-20 (biology)⁠:

• Cryo-EM structure of the bacterial flagellar motor complexed with the hook

• Each subunit in the rod interlocks with adjacent subunits

• 10 peptides, FlgB, and FliE are adaptors that join the MS ring and the rod

• The LP ring applies electrostatic forces to support rotation of the rod

The bacterial flagellar motor is a supramolecular protein machine that drives rotation of the flagellum for motility, which is essential for bacterial survival in different environments and a key determinant of pathogenicity. The detailed structure of the flagellar motor remains unknown. Here we present an atomic-resolution cryoelectron microscopy (cryo-EM) structure of the bacterial flagellar motor complexed with the hook, consisting of 175 subunits with a molecular mass of ~6.3 MDa. The structure reveals that 10 peptides protruding from the MS ring with the FlgB and FliE subunits mediate torque transmission from the MS ring to the rod and overcome the symmetry mismatch between the rotational and helical structures in the motor. The LP ring contacts the distal rod and applies electrostatic forces to support its rotation and torque transmission to the hook. This work provides detailed molecular insights into the structure, assembly, and torque transmission mechanisms of the flagellar motor.

[Keywords: flagellum, bacterial flagellar motor, bacterial motility, LP ring, MS ring, rod, hook, export apparatus, torque transmission, cryoelectron microscopy]