{"title":"Structural basis of the bacterial flagellar motor rotational switching","authors":"Jiaxing Tan, Ling Zhang, Xingtong Zhou, Siyu Han, Yan Zhou, Yongqun Zhu","doi":"10.1038/s41422-024-01017-z","DOIUrl":null,"url":null,"abstract":"The bacterial flagellar motor is a huge bidirectional rotary nanomachine that drives rotation of the flagellum for bacterial motility. The cytoplasmic C ring of the flagellar motor functions as the switch complex for the rotational direction switching from counterclockwise to clockwise. However, the structural basis of the rotational switching and how the C ring is assembled have long remained elusive. Here, we present two high-resolution cryo-electron microscopy structures of the C ring-containing flagellar basal body–hook complex from Salmonella Typhimurium, which are in the default counterclockwise state and in a constitutively active CheY mutant-induced clockwise state, respectively. In both complexes, the C ring consists of four subrings, but is in two different conformations. The CheY proteins are bound into an open groove between two adjacent protomers on the surface of the middle subring of the C ring and interact with the FliG and FliM subunits. The binding of the CheY protein induces a significant upward shift of the C ring towards the MS ring and inward movements of its protomers towards the motor center, which eventually remodels the structures of the FliG subunits and reverses the orientations and surface electrostatic potential of the αtorque helices to trigger the counterclockwise-to-clockwise rotational switching. The conformational changes of the FliG subunits reveal that the stator units on the motor require a relocation process in the inner membrane during the rotational switching. This study provides unprecedented molecular insights into the rotational switching mechanism and a detailed overall structural view of the bacterial flagellar motors.","PeriodicalId":9926,"journal":{"name":"Cell Research","volume":null,"pages":null},"PeriodicalIF":28.1000,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41422-024-01017-z.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Cell Research","FirstCategoryId":"99","ListUrlMain":"https://www.nature.com/articles/s41422-024-01017-z","RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"CELL BIOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
The bacterial flagellar motor is a huge bidirectional rotary nanomachine that drives rotation of the flagellum for bacterial motility. The cytoplasmic C ring of the flagellar motor functions as the switch complex for the rotational direction switching from counterclockwise to clockwise. However, the structural basis of the rotational switching and how the C ring is assembled have long remained elusive. Here, we present two high-resolution cryo-electron microscopy structures of the C ring-containing flagellar basal body–hook complex from Salmonella Typhimurium, which are in the default counterclockwise state and in a constitutively active CheY mutant-induced clockwise state, respectively. In both complexes, the C ring consists of four subrings, but is in two different conformations. The CheY proteins are bound into an open groove between two adjacent protomers on the surface of the middle subring of the C ring and interact with the FliG and FliM subunits. The binding of the CheY protein induces a significant upward shift of the C ring towards the MS ring and inward movements of its protomers towards the motor center, which eventually remodels the structures of the FliG subunits and reverses the orientations and surface electrostatic potential of the αtorque helices to trigger the counterclockwise-to-clockwise rotational switching. The conformational changes of the FliG subunits reveal that the stator units on the motor require a relocation process in the inner membrane during the rotational switching. This study provides unprecedented molecular insights into the rotational switching mechanism and a detailed overall structural view of the bacterial flagellar motors.
细菌鞭毛马达是一个巨大的双向旋转纳米机械,可驱动鞭毛旋转,从而实现细菌的运动。鞭毛马达细胞质中的 C 环是旋转方向从逆时针到顺时针切换的开关复合物。然而,旋转切换的结构基础以及 C 环是如何组装的,长期以来一直是个谜。在这里,我们展示了两种来自鼠伤寒沙门氏菌的含C环的鞭毛基体-钩复合体的高分辨率冷冻电镜结构,它们分别处于默认的逆时针状态和组成型活性CheY突变诱导的顺时针状态。在这两种复合物中,C 环由四个子环组成,但有两种不同的构象。CheY 蛋白结合到 C 环中间亚环表面两个相邻原基之间的开放沟槽中,并与 FliG 和 FliM 亚基相互作用。CheY 蛋白的结合导致 C 环向 MS 环显著上移,其原生体向马达中心内移,最终重塑了 FliG 亚基的结构,扭转了 α 扭转螺旋的方向和表面静电势,引发了逆时针到顺时针的旋转切换。FliG 亚基的构象变化揭示出,在旋转切换过程中,马达上的定子单元需要在内膜上进行重新定位。这项研究为旋转切换机制提供了前所未有的分子见解,并为细菌鞭毛马达提供了详细的整体结构视图。
期刊介绍:
Cell Research (CR) is an international journal published by Springer Nature in partnership with the Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences (CAS). It focuses on publishing original research articles and reviews in various areas of life sciences, particularly those related to molecular and cell biology. The journal covers a broad range of topics including cell growth, differentiation, and apoptosis; signal transduction; stem cell biology and development; chromatin, epigenetics, and transcription; RNA biology; structural and molecular biology; cancer biology and metabolism; immunity and molecular pathogenesis; molecular and cellular neuroscience; plant molecular and cell biology; and omics, system biology, and synthetic biology. CR is recognized as China's best international journal in life sciences and is part of Springer Nature's prestigious family of Molecular Cell Biology journals.