The flagellar motor of Vibrio alginolyticus undergoes major structural remodeling during rotational switching
Brittany L Carroll,
Tatsuro Nishikino,
Wangbiao Guo,
Shiwei Zhu,
Seiji Kojima,
Michio Homma,
Jun Liu
Affiliations
Brittany L Carroll
Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, United States; Microbial Sciences Institute, Yale University, West Haven, United States
Tatsuro Nishikino
Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan
Wangbiao Guo
Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, United States; Microbial Sciences Institute, Yale University, West Haven, United States
Shiwei Zhu
Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, United States; Microbial Sciences Institute, Yale University, West Haven, United States
Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, United States; Microbial Sciences Institute, Yale University, West Haven, United States
The bacterial flagellar motor switches rotational direction between counterclockwise (CCW) and clockwise (CW) to direct the migration of the cell. The cytoplasmic ring (C-ring) of the motor, which is composed of FliG, FliM, and FliN, is known for controlling the rotational sense of the flagellum. However, the mechanism underlying rotational switching remains elusive. Here, we deployed cryo-electron tomography to visualize the C-ring in two rotational biased mutants in Vibrio alginolyticus. We determined the C-ring molecular architectures, providing novel insights into the mechanism of rotational switching. We report that the C-ring maintained 34-fold symmetry in both rotational senses, and the protein composition remained constant. The two structures show FliG conformational changes elicit a large conformational rearrangement of the rotor complex that coincides with rotational switching of the flagellum. FliM and FliN form a stable spiral-shaped base of the C-ring, likely stabilizing the C-ring during the conformational remodeling.