Characterization of C-ring component assembly in flagellar motors from amino acid coevolution

Santos, Ricardo Nascimento dos; Khan, Shahid; Morcos, Faruck

doi:10.1098/rsos.171854

Cited by 13 publications

(8 citation statements)

References 75 publications

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“…The middle domain of FliM (FliM M ) binds to FliG M [79]. The C-terminal domain (FliM C ) dimerizes with FliN [80], which locates at the bottom of the C-ring.…”

Section: Interaction Between the Stator Unit And Rotormentioning

confidence: 99%

Structural basis of torque generation in the bi-directional bacterial flagellar motor

Santiveri

Wadhwa

et al. 2022

Trends in Biochemical Sciences

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The flagellar stator unit is an oligomeric complex of two membrane proteins (MotA 5 B 2 ) that powers bi-directional rotation of the bacterial flagellum. Harnessing the ion motive force across the cytoplasmic membrane, the stator unit operates as a miniature rotary motor itself to provide torque for rotation of the flagellum. Recent cryo-electron microscopic (cryo-EM) structures of the stator unit provided novel insights into its assembly, function, and subunit stoichiometry, revealing the ion flux pathway and the torque generation mechanism. Furthermore, in situ cryoelectron tomography (cryo-ET) studies revealed unprecedented details of the interactions between stator unit and rotor. In this review, we summarize recent advances in our understanding of the structure and function of the flagellar stator unit, torque generation, and directional switching of the motor. The bacterial flagellum and its rotary motorMany bacteria, including Escherichia coli, Salmonella, and Bacillus spp., use flagella (see Glossary) to move through liquid environments and across surfaces. The flagellum is a supramolecular nanomachine that protrudes from the cell envelope and measures~5-20 μm in length. It is able to rotate in both clockwise (CW) and counterclockwise (CCW) directions to propel the bacterial cell body in different living environments [1,2]. Rotational switching between these two modes is regulated by chemotactic signaling, which is a rapid process that responds to environmental stimuli and biases movement of the cell toward attractants and away from repellents. Flagella-mediated chemotaxis further enables pathogenic bacteria to move toward cells to establish in vivo niches. [3,4]. Thus, flagella have fundamental roles in bacterial locomotion and virulence [5].The flagellum comprises more than 25 kinds of building blocks, which assemble in a highly ordered manner. The flagellar structure can be divided into three morphologically distinguishable parts: a cell envelope-spanning motor (basal body), a universal joint (hook), and a long, thin helical filament [6,7] (Figure 1). Among them, the most intricate part is the basal body, containing the components responsible for assembly of the flagellum [the flagellar-specific type-III secretion system (T3SS) [8]], torque generation (the stator units [9]), and rotational switching (binding of the response regulator CheY-P to the cytoplasmic C-ring [10,11]). Cryo-ET studies of the motor from different bacterial species show the variation of its structure, while the core components are conserved [7,12,13]. For example, in the Gram-negative bacteria Salmonella and E. coli, the flagellar motor contains four ring-like structures based on their distributions relative to the cell surface layers [lipopolysaccharide (L-)ring, peptidoglycan (P-)ring, inner membrane/ supramembrane (MS-)ring, and cytoplasmic (C-)ring] surrounding a central rigid rod [14][15][16][17]. Additional ring-like structures, H-and T-rings, located in the periplasmic space, have also been observed in Vibrio spp [18]. It i...

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“…The middle domain of FliM (FliM M ) binds to FliG M [79]. The C-terminal domain (FliM C ) dimerizes with FliN [80], which locates at the bottom of the C-ring.…”

Section: Interaction Between the Stator Unit And Rotormentioning

confidence: 99%

Structural basis of torque generation in the bi-directional bacterial flagellar motor

Santiveri

Wadhwa

et al. 2022

Trends in Biochemical Sciences

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“…The FliM M serves as a connection between the base of the C-ring and FliG ( Brown et al, 2002 ; Minamino et al, 2011 ). FliM C forms a heterodimer with FliN when fused via a flexible linker ( Notti et al, 2015 ; Dos Santos et al, 2018 ). The third protein, FliN, a small single-domain protein, dimerizes with FliM or itself to form the base of the C-ring ( Brown et al, 2005 ).…”

Section: Introductionmentioning

confidence: 99%

The flagellar motor of Vibrio alginolyticus undergoes major structural remodeling during rotational switching

Carroll

Nishikino

Guo

et al. 2020

eLife

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The bacterial flagellar motor switches rotational directions 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.

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“…First, the role of FliM M as the central relay was consistent with its strongly coevolved inter-subunit and FliG M interfacial contacts [110]. Two distinct T. maritima FliM M dimer configurations were obtained when dimer formation was simulated based on coevolved subunit couplings [111], although one orientation did not match either the CW and CCW dimers deduced from S. enterica residue substitutions [76], either because of limited sampling and/or because the bi-directional switch is not universal across species. Secondly, coevolution provided strong support for conservation of the FliG C -FliG M stacking contact [109,112] relative to other contacts identified by cross-link data [77].…”

Section: Bidirectional Torque Generation-flig M -Flig C Interactionsmentioning

confidence: 75%

The Architectural Dynamics of the Bacterial Flagellar Motor Switch

Khan

2020

Biomolecules

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The rotary bacterial flagellar motor is remarkable in biochemistry for its highly synchronized operation and amplification during switching of rotation sense. The motor is part of the flagellar basal body, a complex multi-protein assembly. Sensory and energy transduction depends on a core of six proteins that are adapted in different species to adjust torque and produce diverse switches. Motor response to chemotactic and environmental stimuli is driven by interactions of the core with small signal proteins. The initial protein interactions are propagated across a multi-subunit cytoplasmic ring to switch torque. Torque reversal triggers structural transitions in the flagellar filament to change motile behavior. Subtle variations in the core components invert or block switch operation. The mechanics of the flagellar switch have been studied with multiple approaches, from protein dynamics to single molecule and cell biophysics. The architecture, driven by recent advances in electron cryo-microscopy, is available for several species. Computational methods have correlated structure with genetic and biochemical databases. The design principles underlying the basis of switch ultra-sensitivity and its dependence on motor torque remain elusive, but tantalizing clues have emerged. This review aims to consolidate recent knowledge into a unified platform that can inspire new research strategies.

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Characterization of C-ring component assembly in flagellar motors from amino acid coevolution

Cited by 13 publications

References 75 publications

Structural basis of torque generation in the bi-directional bacterial flagellar motor

Structural basis of torque generation in the bi-directional bacterial flagellar motor

The flagellar motor of Vibrio alginolyticus undergoes major structural remodeling during rotational switching

The Architectural Dynamics of the Bacterial Flagellar Motor Switch

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