Molecular mechanism for rotational switching of the bacterial flagellar motor

• Published in: Nature structural & molecular biology Vol. 27; no. 11; pp. 1041 - 1047
• Main Authors: Chang, Yunjie, Zhang, Kai, Carroll, Brittany L., Zhao, Xiaowei, Charon, Nyles W., Norris, Steven J., Motaleb, Md A., Li, Chunhao, Liu, Jun
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01.11.2020; Nature Publishing Group
• Subjects: 14/28; 631/326/88; 631/57/343/2277; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bacterial Proteins - ultrastructure; Biochemistry; Biological Microscopy; Biomedical and Life Sciences; Borrelia burgdorferi; Borrelia burgdorferi - chemistry; Borrelia burgdorferi - metabolism; Borrelia burgdorferi - ultrastructure; Cryoelectron Microscopy; E coli; Flagella; Flagella - chemistry; Flagella - metabolism; Flagella - ultrastructure; Immunology; Life Sciences; Membrane Biology; Models, Molecular; Molecular biology; Motility; Protein Binding; Protein Conformation; Protein Interaction Maps; Protein Structure; Proteins; Proton-Motive Force; Protonmotive force; Rotation; Switching; Torque
• ISSN: 1545-9993; 1545-9985
• DOI: 10.1038/s41594-020-0497-2

The bacterial flagellar motor can rotate in counterclockwise (CCW) or clockwise (CW) senses, and transitions are controlled by the phosphorylated form of the response regulator CheY (CheY-P). To dissect the mechanism underlying flagellar rotational switching, we use Borrelia burgdorferi as a model system to determine high-resolution in situ motor structures in cheX and cheY3 mutants, in which motors are locked in either CCW or CW rotation. The structures showed that CheY3-P interacts directly with a switch protein, FliM, inducing a major remodeling of another switch protein, FliG2, and altering its interaction with the torque generator. Our findings lead to a model in which the torque generator rotates in response to an inward flow of H + driven by the proton motive force, and conformational changes in FliG2 driven by CheY3-P allow the switch complex to interact with opposite sides of the rotating torque generator, facilitating rotational switching. In situ cryo-ET analyses of Borrelia burgdorferi flagellar motors locked in clockwise or counterclockwise rotation provide insights into rotational switching.