Structure and Function of Stator Units of the Bacterial Flagellar Motor

• Published in: Cell 2020-10, Vol.183 (1), p.244-257.e16
• Main Authors: Santiveri, Mònica, Roa-Eguiara, Aritz, Kühne, Caroline, Wadhwa, Navish, Hu, Haidai, Berg, Howard C., Erhardt, Marc, Taylor, Nicholas M.I.
• Format: Article
• Language: English
• Subjects: bacterial flagellar motor; chemotaxis; cryo-electron; ion channel; microbiology; microscopy; motility; stator unit; structural biology; torque generation
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2020.08.016

Many bacteria use the flagellum for locomotion and chemotaxis. Its bidirectional rotation is driven by a membrane-embedded motor, which uses energy from the transmembrane ion gradient to generate torque at the interface between stator units and rotor. The structural organization of the stator unit (MotAB), its conformational changes upon ion transport, and how these changes power rotation of the flagellum remain unknown. Here, we present ~3 Å-resolution cryoelectron microscopy reconstructions of the stator unit in different functional states. We show that the stator unit consists of a dimer of MotB surrounded by a pentamer of MotA. Combining structural data with mutagenesis and functional studies, we identify key residues involved in torque generation and present a detailed mechanistic model for motor function and switching of rotational direction. [Display omitted] •Structure of MotAB flagellar stator unit in different functional states by cryo-EM•5:2 stoichiometry is conserved across the MotAB/PomAB family•Conformational changes upon protonation•MotB2 drives rotation of surrounding MotA5, which engages the rotor to generate torque Structures of the MotAB stator unit reveal how its conformational changes, coupled to ion transport, provide torque to power the rotation of the bacterial flagellum.