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Minamino T, Kinoshita M. Structure, Assembly, and Function of Flagella Responsible for Bacterial Locomotion. EcoSal Plus 2023; 11:eesp00112023. [PMID: 37260402 PMCID: PMC10729930 DOI: 10.1128/ecosalplus.esp-0011-2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Accepted: 04/14/2023] [Indexed: 01/28/2024]
Abstract
Many motile bacteria use flagella for locomotion under a variety of environmental conditions. Because bacterial flagella are under the control of sensory signal transduction pathways, each cell is able to autonomously control its flagellum-driven locomotion and move to an environment favorable for survival. The flagellum of Salmonella enterica serovar Typhimurium is a supramolecular assembly consisting of at least three distinct functional parts: a basal body that acts as a bidirectional rotary motor together with multiple force generators, each of which serves as a transmembrane proton channel to couple the proton flow through the channel with torque generation; a filament that functions as a helical propeller that produces propulsion; and a hook that works as a universal joint that transmits the torque produced by the rotary motor to the helical propeller. At the base of the flagellum is a type III secretion system that transports flagellar structural subunits from the cytoplasm to the distal end of the growing flagellar structure, where assembly takes place. In recent years, high-resolution cryo-electron microscopy (cryoEM) image analysis has revealed the overall structure of the flagellum, and this structural information has made it possible to discuss flagellar assembly and function at the atomic level. In this article, we describe what is known about the structure, assembly, and function of Salmonella flagella.
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Affiliation(s)
- Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Miki Kinoshita
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
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2
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Spirochete Flagella and Motility. Biomolecules 2020; 10:biom10040550. [PMID: 32260454 PMCID: PMC7225975 DOI: 10.3390/biom10040550] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 04/03/2020] [Accepted: 04/03/2020] [Indexed: 02/07/2023] Open
Abstract
Spirochetes can be distinguished from other flagellated bacteria by their long, thin, spiral (or wavy) cell bodies and endoflagella that reside within the periplasmic space, designated as periplasmic flagella (PFs). Some members of the spirochetes are pathogenic, including the causative agents of syphilis, Lyme disease, swine dysentery, and leptospirosis. Furthermore, their unique morphologies have attracted attention of structural biologists; however, the underlying physics of viscoelasticity-dependent spirochetal motility is a longstanding mystery. Elucidating the molecular basis of spirochetal invasion and interaction with hosts, resulting in the appearance of symptoms or the generation of asymptomatic reservoirs, will lead to a deeper understanding of host-pathogen relationships and the development of antimicrobials. Moreover, the mechanism of propulsion in fluids or on surfaces by the rotation of PFs within the narrow periplasmic space could be a designing base for an autonomously driving micro-robot with high efficiency. This review describes diverse morphology and motility observed among the spirochetes and further summarizes the current knowledge on their mechanisms and relations to pathogenicity, mainly from the standpoint of experimental biophysics.
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Nakamura S, Hanaizumi Y, Morimoto YV, Inoue Y, Erhardt M, Minamino T, Namba K. Direct observation of speed fluctuations of flagellar motor rotation at extremely low load close to zero. Mol Microbiol 2019; 113:755-765. [DOI: 10.1111/mmi.14440] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 12/10/2019] [Accepted: 12/10/2019] [Indexed: 12/22/2022]
Affiliation(s)
- Shuichi Nakamura
- Department of Applied Physics, Graduate School of Engineering Tohoku University Sendai Japan
| | - Yuta Hanaizumi
- Department of Applied Physics, Graduate School of Engineering Tohoku University Sendai Japan
| | - Yusuke V. Morimoto
- Faculty of Computer Science and Systems Engineering, Department of Physics and Information Technology Kyushu Institute of Technology Fukuoka Japan
| | - Yumi Inoue
- Graduate School of Frontier Biosciences Osaka University Osaka Japan
| | - Marc Erhardt
- Institut für Biologie/Bakterienphysiologie Humboldt‐Universität zu Berlin Berlin Germany
| | - Tohru Minamino
- Graduate School of Frontier Biosciences Osaka University Osaka Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences Osaka University Osaka Japan
- RIKEN Spring‐8 Center and Center for Biosystems Dynamics Research Osaka Japan
- JEOL YOKOGUSHI Research Alliance Laboratories Osaka University Osaka Japan
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4
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Onoue Y, Iwaki M, Shinobu A, Nishihara Y, Iwatsuki H, Terashima H, Kitao A, Kandori H, Homma M. Essential ion binding residues for Na + flow in stator complex of the Vibrio flagellar motor. Sci Rep 2019; 9:11216. [PMID: 31375690 PMCID: PMC6677748 DOI: 10.1038/s41598-019-46038-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Accepted: 06/17/2019] [Indexed: 01/06/2023] Open
Abstract
The bacterial flagellar motor is a unique supramolecular complex which converts ion flow into rotational force. Many biological devices mainly use two types of ions, proton and sodium ion. This is probably because of the fact that life originated in seawater, which is rich in protons and sodium ions. The polar flagellar motor in Vibrio is coupled with sodium ion and the energy converting unit of the motor is composed of two membrane proteins, PomA and PomB. It has been shown that the ion binding residue essential for ion transduction is the conserved aspartic acid residue (PomB-D24) in the PomB transmembrane region. To reveal the mechanism of ion selectivity, we identified essential residues, PomA-T158 and PomA-T186, other than PomB-D24, in the Na+-driven flagellar motor. It has been shown that the side chain of threonine contacts Na+ in Na+-coupled transporters. We monitored the Na+-binding specific structural changes using ATR-FTIR spectroscopy. The signals were abolished in PomA-T158A and -T186A, as well as in PomB-D24N. Molecular dynamics simulations further confirmed the strong binding of Na+ to D24 and showed that T158A and T186A hindered the Na+ binding and transportation. The data indicate that two threonine residues (PomA-T158 and PomA-T186), together with PomB-D24, are important for Na+ conduction in the Vibrio flagellar motor. The results contribute to clarify the mechanism of ion recognition and conversion of ion flow into mechanical force.
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Affiliation(s)
- Yasuhiro Onoue
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan
| | - Masayo Iwaki
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Showa-ku, Nagoya, 466-8555, Japan
| | - Ai Shinobu
- School of Life Science and Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan
| | - Yasutaka Nishihara
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032, Japan
| | - Hiroto Iwatsuki
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan
| | - Hiroyuki Terashima
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan
| | - Akio Kitao
- School of Life Science and Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan
| | - Hideki Kandori
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Showa-ku, Nagoya, 466-8555, Japan.
| | - Michio Homma
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan.
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Flagella-Driven Motility of Bacteria. Biomolecules 2019; 9:biom9070279. [PMID: 31337100 PMCID: PMC6680979 DOI: 10.3390/biom9070279] [Citation(s) in RCA: 181] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 07/11/2019] [Accepted: 07/12/2019] [Indexed: 01/17/2023] Open
Abstract
The bacterial flagellum is a helical filamentous organelle responsible for motility. In bacterial species possessing flagella at the cell exterior, the long helical flagellar filament acts as a molecular screw to generate thrust. Meanwhile, the flagella of spirochetes reside within the periplasmic space and not only act as a cytoskeleton to determine the helicity of the cell body, but also rotate or undulate the helical cell body for propulsion. Despite structural diversity of the flagella among bacterial species, flagellated bacteria share a common rotary nanomachine, namely the flagellar motor, which is located at the base of the filament. The flagellar motor is composed of a rotor ring complex and multiple transmembrane stator units and converts the ion flux through an ion channel of each stator unit into the mechanical work required for motor rotation. Intracellular chemotactic signaling pathways regulate the direction of flagella-driven motility in response to changes in the environments, allowing bacteria to migrate towards more desirable environments for their survival. Recent experimental and theoretical studies have been deepening our understanding of the molecular mechanisms of the flagellar motor. In this review article, we describe the current understanding of the structure and dynamics of the bacterial flagellum.
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Effect of the MotA(M206I) Mutation on Torque Generation and Stator Assembly in the Salmonella H +-Driven Flagellar Motor. J Bacteriol 2019; 201:JB.00727-18. [PMID: 30642987 DOI: 10.1128/jb.00727-18] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Accepted: 01/03/2019] [Indexed: 12/20/2022] Open
Abstract
The bacterial flagellar motor is composed of a rotor and a dozen stators and converts the ion flux through the stator into torque. Each stator unit alternates in its attachment to and detachment from the rotor even during rotation. In some species, stator assembly depends on the input energy, but it remains unclear how an electrochemical potential across the membrane (e.g., proton motive force [PMF]) or ion flux is involved in stator assembly dynamics. Here, we focused on pH dependence of a slow motile MotA(M206I) mutant of Salmonella The MotA(M206I) motor produces torque comparable to that of the wild-type motor near stall, but its rotation rate is considerably decreased as the external load is reduced. Rotation assays of flagella labeled with 1-μm beads showed that the rotation rate of the MotA(M206I) motor is increased by lowering the external pH whereas that of the wild-type motor is not. Measurements of the speed produced by a single stator unit using 1-μm beads showed that the unit speed of the MotA(M206I) is about 60% of that of the wild-type and that a decrease in external pH did not affect the MotA(M206I) unit speed. Analysis of the subcellular stator localization revealed that the number of functional stators is restored by lowering the external pH. The pH-dependent improvement of stator assembly was observed even when the PMF was collapsed and proton transfer was inhibited. These results suggest that MotA-Met206 is responsible for not only load-dependent energy coupling between the proton influx and rotation but also pH-dependent stator assembly.IMPORTANCE The bacterial flagellar motor is a rotary nanomachine driven by the electrochemical transmembrane potential (ion motive force). About 10 stators (MotA/MotB complexes) are docked around a rotor, and the stator recruitment depends on the load, ion motive force, and coupling ion flux. The MotA(M206I) mutation slows motor rotation and decreases the number of docked stators in Salmonella We show that lowering the external pH improves the assembly of the mutant stators. Neither the collapse of the ion motive force nor a mutation mimicking the proton-binding state inhibited stator localization to the motor. These results suggest that MotA-Met206 is involved in torque generation and proton translocation and that stator assembly is stabilized by protonation of the stator.
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Abstract
Bacteria, life living at microscale, can spread only by thermal fluctuation. However, the ability of directional movement, such as swimming by rotating flagella, gliding over surfaces via mobile cell-surface adhesins, and actin-dependent movement, could be useful for thriving through searching more favorable environments, and such motility is known to be related to pathogenicity. Among diverse migration mechanisms, perhaps flagella-dependent motility would be used by most species. The bacterial flagellum is a molecular nanomachine comprising a helical filament and a basal motor, which is fueled by an electrochemical gradient of cation across the cell membrane (ion motive force). Many species, such as Escherichia coli, possess flagella on the outside of the cell body, whereas flagella of spirochetes reside within the periplasmic space. Flagellar filaments or helical spirochete bodies rotate like a screw propeller, generating propulsive force. This review article describes the current knowledge of the structure and operation mechanism of the bacterial flagellum, and flagella-dependent motility in highly viscous environments.
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Affiliation(s)
- Shuichi Nakamura
- Department of Applied Physics, Graduate School of Engineering, Tohoku University
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8
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Minamino T, Terahara N, Kojima S, Namba K. Autonomous control mechanism of stator assembly in the bacterial flagellar motor in response to changes in the environment. Mol Microbiol 2018; 109:723-734. [DOI: 10.1111/mmi.14092] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Revised: 07/26/2018] [Accepted: 07/28/2018] [Indexed: 01/02/2023]
Affiliation(s)
- Tohru Minamino
- Graduate School of Frontier Biosciences Osaka University 1‐3 YamadaokaSuita Osaka 565‐0871Japan
| | - Naoya Terahara
- Graduate School of Frontier Biosciences Osaka University 1‐3 YamadaokaSuita Osaka 565‐0871Japan
| | - Seiji Kojima
- Division of Biological Science, Graduate School of Science Nagoya University Chikusa‐kuNagoya 464‐8602Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences Osaka University 1‐3 YamadaokaSuita Osaka 565‐0871Japan
- RIKEN Center for Biosystems Dynamics Research & SPring‐8 Center 1‐3 YamadaokaSuita Osaka 565‐0871Japan
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9
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Pourjaberi SNS, Terahara N, Namba K, Minamino T. The role of a cytoplasmic loop of MotA in load-dependent assembly and disassembly dynamics of the MotA/B stator complex in the bacterial flagellar motor. Mol Microbiol 2017; 106:646-658. [DOI: 10.1111/mmi.13843] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/18/2017] [Indexed: 11/26/2022]
Affiliation(s)
| | - Naoya Terahara
- Graduate School of Frontier Biosciences; Osaka University, 1-3 Yamadaoka; Suita Osaka 565-0871 Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences; Osaka University, 1-3 Yamadaoka; Suita Osaka 565-0871 Japan
- RIKEN; Quantitative Biology Center, 1-3 Yamadaoka; Suita Osaka 565-0871 Japan
| | - Tohru Minamino
- Graduate School of Frontier Biosciences; Osaka University, 1-3 Yamadaoka; Suita Osaka 565-0871 Japan
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10
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Nakamura S, Minamino T, Kami-Ike N, Kudo S, Namba K. Effect of the MotB(D33N) mutation on stator assembly and rotation of the proton-driven bacterial flagellar motor. Biophysics (Nagoya-shi) 2014; 10:35-41. [PMID: 27493496 PMCID: PMC4629662 DOI: 10.2142/biophysics.10.35] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 05/28/2014] [Indexed: 01/21/2023] Open
Abstract
The bacterial flagellar motor generates torque by converting the energy of proton translocation through the transmembrane proton channel of the stator complex formed by MotA and MotB. The MotA/B complex is thought to be anchored to the peptidoglycan (PG) layer through the PG-binding domain of MotB to act as the stator. The stator units dynamically associate with and dissociate from the motor during flagellar motor rotation, and an electrostatic interaction between MotA and a rotor protein FliG is required for efficient stator assembly. However, the association and dissociation mechanism of the stator units still remains unclear. In this study, we analyzed the speed fluctuation of the flagellar motor of Salmonella enterica wild-type cells carrying a plasmid encoding a nonfunctional stator complex, MotA/B(D33N), which lost the proton conductivity. The wild-type motor rotated stably but the motor speed fluctuated considerably when the expression level of MotA/B(D33N) was relatively high compared to MotA/B. Rapid accelerations and decelerations were frequently observed. A quantitative analysis of the speed fluctuation and a model simulation suggested that the MotA/B(D33N) stator retains the ability to associate with the motor at a low affinity but dissociates more rapidly than the MotA/B stator. We propose that the stator dissociation process depends on proton translocation through the proton channel.
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Affiliation(s)
- Shuichi Nakamura
- Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba, Aoba-ku, Sendai 980-8579, Japan
| | - Tohru Minamino
- Graduate School of Frontier Bioscience, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Nobunori Kami-Ike
- Graduate School of Frontier Bioscience, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Seishi Kudo
- Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba, Aoba-ku, Sendai 980-8579, Japan
| | - Keiichi Namba
- Graduate School of Frontier Bioscience, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan; Riken Quantitative Biology Center, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
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11
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Morimoto YV, Minamino T. Structure and function of the bi-directional bacterial flagellar motor. Biomolecules 2014; 4:217-34. [PMID: 24970213 PMCID: PMC4030992 DOI: 10.3390/biom4010217] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Revised: 01/24/2014] [Accepted: 02/04/2014] [Indexed: 01/02/2023] Open
Abstract
The bacterial flagellum is a locomotive organelle that propels the bacterial cell body in liquid environments. The flagellum is a supramolecular complex composed of about 30 different proteins and consists of at least three parts: a rotary motor, a universal joint, and a helical filament. The flagellar motor of Escherichia coli and Salmonella enterica is powered by an inward-directed electrochemical potential difference of protons across the cytoplasmic membrane. The flagellar motor consists of a rotor made of FliF, FliG, FliM and FliN and a dozen stators consisting of MotA and MotB. FliG, FliM and FliN also act as a molecular switch, enabling the motor to spin in both counterclockwise and clockwise directions. Each stator is anchored to the peptidoglycan layer through the C-terminal periplasmic domain of MotB and acts as a proton channel to couple the proton flow through the channel with torque generation. Highly conserved charged residues at the rotor–stator interface are required not only for torque generation but also for stator assembly around the rotor. In this review, we will summarize our current understanding of the structure and function of the proton-driven bacterial flagellar motor.
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Affiliation(s)
- Yusuke V Morimoto
- Quantitative Biology Center, RIKEN, 6-2-3 Furuedai, Suita, Osaka 565-0874, Japan.
| | - Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.
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12
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Castillo DJ, Nakamura S, Morimoto YV, Che YS, Kami-Ike N, Kudo S, Minamino T, Namba K. The C-terminal periplasmic domain of MotB is responsible for load-dependent control of the number of stators of the bacterial flagellar motor. Biophysics (Nagoya-shi) 2013; 9:173-81. [PMID: 27493556 PMCID: PMC4629673 DOI: 10.2142/biophysics.9.173] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Accepted: 12/07/2013] [Indexed: 12/29/2022] Open
Abstract
The bacterial flagellar motor is made of a rotor and stators. In Salmonella it is thought that about a dozen MotA/B complexes are anchored to the peptidoglycan layer around the motor through the C-terminal peptidoglycan-binding domain of MotB to become active stators as well as proton channels. MotB consists of 309 residues, forming a single transmembrane helix (30–50), a stalk (51–100) and a C-terminal peptidoglycan-binding domain (101–309). Although the stalk is dispensable for torque generation by the motor, it is required for efficient motor performance. Residues 51 to 72 prevent premature proton leakage through the proton channel prior to stator assembly into the motor. However, the role of residues 72–100 remains unknown. Here, we analyzed the torque-speed relationship of the MotB(Δ72–100) motor. At a low speed near stall, this mutant motor produced torque at the wild-type level. Unlike the wild-type motor, however, torque dropped off drastically by slight decrease in external load and then showed a slow exponential decay over a wide range of load by its further reduction. Since it is known that the stator is a mechano-sensor and that the number of active stators changes in a load-dependent manner, we interpreted this unusual torque-speed relationship as anomaly in load-dependent control of the number of active stators. The results suggest that residues 72–100 of MotB is required for proper load-dependent control of the number of active stators around the rotor.
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Affiliation(s)
- David J Castillo
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Shuichi Nakamura
- Department of Applied Physics, Tohoku University, 6-6-05 Aoba, Aramakiaza, Aoba-ku, Sendai, Miyagi 980-8579, Japan
| | - Yusuke V Morimoto
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan; Quantitative Biology Center, RIKEN, 6-2-3 Furuedai, Suita, Osaka 565-0874, Japan
| | - Yong-Suk Che
- Department of Frontier Bioscience, Hosei University, 3-7-2 Kajino-cho, Koganei, Tokyo 184-8584, Japan
| | - Nobunori Kami-Ike
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Seishi Kudo
- Department of Applied Physics, Tohoku University, 6-6-05 Aoba, Aramakiaza, Aoba-ku, Sendai, Miyagi 980-8579, Japan
| | - Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan; Quantitative Biology Center, RIKEN, 6-2-3 Furuedai, Suita, Osaka 565-0874, Japan
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13
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Che YS, Nakamura S, Morimoto YV, Kami-Ike N, Namba K, Minamino T. Load-sensitive coupling of proton translocation and torque generation in the bacterial flagellar motor. Mol Microbiol 2013; 91:175-84. [PMID: 24255940 DOI: 10.1111/mmi.12453] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/04/2013] [Indexed: 01/02/2023]
Abstract
The Salmonella flagellar motor consists of a rotor and about a dozen stator elements. Each stator element, consisting of MotA and MotB, acts as a proton channel to couple proton flow with torque generation. A highly conserved Asp33 residue of MotB is directly involved in the energy coupling mechanism, but it remains unknown how it carries out this function. Here, we show that the MotB(D33E) mutation dramatically alters motor performance in response to changes in external load. Rotation speeds of the MotA/B(D33E) and MotA(V35F)/B(D33E) motors were markedly slower than the wild-type motor and fluctuated considerably at low load but not at high load, whereas the rotation rate of the wild-type motor was stable at any load. At low load, pausing events were frequently observed in both mutant motors. The proton conductivities of these mutant stator channels in their 'unplugged' forms were only half of the conductivity of the wild-type channel. These results suggest that the D33E mutation induces a load-dependent inactivation of the MotA/B complex. We propose that the stator element is a load-sensitive proton channel that efficiently couples proton translocation with torque generation and that Asp33 of MotB is critical for this co-ordinated proton translocation.
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Affiliation(s)
- Yong-Suk Che
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan; Department of Frontier Bioscience, Hosei University, 3-7-2 Kajino-cho, Koganei, Tokyo, 184-8584, Japan
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Mutations in Escherichia coli ExbB transmembrane domains identify scaffolding and signal transduction functions and exclude participation in a proton pathway. J Bacteriol 2013; 195:2898-911. [PMID: 23603742 DOI: 10.1128/jb.00017-13] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The TonB system couples cytoplasmic membrane proton motive force (pmf) to active transport of diverse nutrients across the outer membrane. Current data suggest that cytoplasmic membrane proteins ExbB and ExbD harness pmf energy. Transmembrane domain (TMD) interactions between TonB and ExbD allow the ExbD C terminus to modulate conformational rearrangements of the periplasmic TonB C terminus in vivo. These conformational changes somehow allow energization of high-affinity TonB-gated transporters by direct interaction with TonB. While ExbB is essential for energy transduction, its role is not well understood. ExbB has N-terminus-out, C-terminus-in topology with three TMDs. TMDs 1 and 2 are punctuated by a cytoplasmic loop, with the C-terminal tail also occupying the cytoplasm. We tested the hypothesis that ExbB TMD residues play roles in proton translocation. Reassessment of TMD boundaries based on hydrophobic character and residue conservation among distantly related ExbB proteins brought earlier widely divergent predictions into congruence. All TMD residues with potentially function-specific side chains (Lys, Cys, Ser, Thr, Tyr, Glu, and Asn) and residues with probable structure-specific side chains (Trp, Gly, and Pro) were substituted with Ala and evaluated in multiple assays. While all three TMDs were essential, they had different roles: TMD1 was a region through which ExbB interacted with the TonB TMD. TMD2 and TMD3, the most conserved among the ExbB/TolQ/MotA/PomA family, played roles in signal transduction between cytoplasm and periplasm and the transition from ExbB homodimers to homotetramers. Consideration of combined data excludes ExbB TMD residues from direct participation in a proton pathway.
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15
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Distinct roles of highly conserved charged residues at the MotA-FliG interface in bacterial flagellar motor rotation. J Bacteriol 2012; 195:474-81. [PMID: 23161029 DOI: 10.1128/jb.01971-12] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Electrostatic interactions between the stator protein MotA and the rotor protein FliG are important for bacterial flagellar motor rotation. Arg90 and Glu98 of MotA are required not only for torque generation but also for stator assembly around the rotor, but their actual roles remain unknown. Here we analyzed the roles of functionally important charged residues at the MotA-FliG interface in motor performance. About 75% of the motA(R90E) cells and 45% of the motA(E98K) cells showed no fluorescent spots of green fluorescent protein (GFP)-MotB, indicating reduced efficiency of stator assembly around the rotor. The FliG(D289K) and FliG(R281V) mutations, which restore the motility of the motA(R90E) and motA(E98K) mutants, respectively, showed reduced numbers and intensity of GFP-MotB spots as well. The FliG(D289K) mutation significantly recovered the localization of GFP-MotB to the motor in the motA(R90E) mutant, whereas the FliG(R281V) mutation did not recover the GFP-MotB localization in the motA(E98K) mutant. These results suggest that the MotA-Arg90-FliG-Asp289 interaction is critical for the proper positioning of the stators around the rotor, whereas the MotA-Glu98-FliG-Arg281 interaction is more important for torque generation.
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Microscopic analysis of bacterial motility at high pressure. Biophys J 2012; 102:1872-80. [PMID: 22768943 DOI: 10.1016/j.bpj.2012.03.033] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2011] [Revised: 03/07/2012] [Accepted: 03/12/2012] [Indexed: 12/13/2022] Open
Abstract
The bacterial flagellar motor is a molecular machine that converts an ion flux to the rotation of a helical flagellar filament. Counterclockwise rotation of the filaments allows them to join in a bundle and propel the cell forward. Loss of motility can be caused by environmental factors such as temperature, pH, and solvation. Hydrostatic pressure is also a physical inhibitor of bacterial motility, but the detailed mechanism of this inhibition is still unknown. Here, we developed a high-pressure microscope that enables us to acquire high-resolution microscopic images, regardless of applied pressures. We also characterized the pressure dependence of the motility of swimming Escherichia coli cells and the rotation of single flagellar motors. The fraction and speed of swimming cells decreased with increased pressure. At 80 MPa, all cells stopped swimming and simply diffused in solution. After the release of pressure, most cells immediately recovered their initial motility. Direct observation of the motility of single flagellar motors revealed that at 80 MPa, the motors generate torque that should be sufficient to join rotating filaments in a bundle. The discrepancy in the behavior of free swimming cells and individual motors could be due to the applied pressure inhibiting the formation of rotating filament bundles that can propel the cell body in an aqueous environment.
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Minamino T, Imada K, Kinoshita M, Nakamura S, Morimoto YV, Namba K. Structural insight into the rotational switching mechanism of the bacterial flagellar motor. PLoS Biol 2011; 9:e1000616. [PMID: 21572987 PMCID: PMC3091841 DOI: 10.1371/journal.pbio.1000616] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2010] [Accepted: 03/29/2011] [Indexed: 01/09/2023] Open
Abstract
Structural analysis of a clockwise-biased rotation mutant of the bacterial
flagellar rotor protein FliG provides a new model for the arrangement of FliG
subunits in the motor, and novel insights into rotation switching. The bacterial flagellar motor can rotate either clockwise (CW) or
counterclockwise (CCW). Three flagellar proteins, FliG, FliM, and FliN, are
required for rapid switching between the CW and CCW directions. Switching is
achieved by a conformational change in FliG induced by the binding of a
chemotaxis signaling protein, phospho-CheY, to FliM and FliN. FliG consists of
three domains, FliGN, FliGM, and FliGC, and
forms a ring on the cytoplasmic face of the MS ring of the flagellar basal body.
Crystal structures have been reported for the FliGMC domains of
Thermotoga maritima, which consist of the FliGM
and FliGC domains and a helix E that connects these two domains, and
full-length FliG of Aquifex aeolicus. However, the basis for
the switching mechanism is based only on previously obtained genetic data and is
hence rather indirect. We characterized a CW-biased mutant
(fliG(ΔPAA)) of Salmonella enterica by
direct observation of rotation of a single motor at high temporal and spatial
resolution. We also determined the crystal structure of the FliGMC
domains of an equivalent deletion mutant variant of T. maritima
(fliG(ΔPEV)). The FliG(ΔPAA) motor produced torque
at wild-type levels under a wide range of external load conditions. The
wild-type motors rotated exclusively in the CCW direction under our experimental
conditions, whereas the mutant motors rotated only in the CW direction. This
result suggests that wild-type FliG is more stable in the CCW state than in the
CW state, whereas FliG(ΔPAA) is more stable in the CW state than in the CCW
state. The structure of the TM-FliGMC(ΔPEV) revealed that
extremely CW-biased rotation was caused by a conformational change in helix E.
Although the arrangement of FliGC relative to FliGM in a
single molecule was different among the three crystals, a conserved
FliGM-FliGC unit was observed in all three of them. We
suggest that the conserved FliGM-FliGC unit is the basic
functional element in the rotor ring and that the PAA deletion induces a
conformational change in a hinge-loop between FliGM and helix E to
achieve the CW state of the FliG ring. We also propose a novel model for the
arrangement of FliG subunits within the motor. The model is in agreement with
the previous mutational and cross-linking experiments and explains the
cooperative switching mechanism of the flagellar motor. The bacterial flagellum is a rotating organelle that governs cell motility. At
the base of each flagellum is a motor powered by the electrochemical potential
difference of specific ions across the cytoplasmic membrane. In response to
environmental stimuli, rotation of the motor switches between counterclockwise
and clockwise, with a corresponding effect on the swimming direction of the
cell. Switching is triggered by the binding of the signaling protein
phospho-CheY to FliM and FliN, and achieved by conformational changes in the
rotor protein FliG. The actual switching mechanism, however, remains unclear. In
this study, we characterized a fliG mutant of
Salmonella that shows an extreme clockwise-biased rotation,
and determined the structure of a fragment of FliG (FliGMC) of the
equivalent mutant variant of Thermotoga maritima.
FliGMC is composed of two domains and covers the regions
essential for torque generation and FliM binding. We showed that the mutant
structure has a conformational change in the helix connecting the two domains,
leading to a domain orientation distinct from that of the wild-type FliG. On the
basis of this structure, we propose a new model for the arrangement of FliG
subunits in the rotor that is consistent with the previous mutational studies
and explains how cooperative switching occurs in the motor.
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Affiliation(s)
- Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka
University, Osaka, Japan
- PRESTO, JST, Saitama, Japan
| | - Katsumi Imada
- Graduate School of Frontier Biosciences, Osaka
University, Osaka, Japan
- Department of Macromolecular Science, Osaka
University, Osaka, Japan
- * E-mail: (KI); (KN)
| | - Miki Kinoshita
- Graduate School of Frontier Biosciences, Osaka
University, Osaka, Japan
| | - Shuichi Nakamura
- Graduate School of Frontier Biosciences, Osaka
University, Osaka, Japan
| | | | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka
University, Osaka, Japan
- * E-mail: (KI); (KN)
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Kuehl CJ, Crosa JH. The TonB energy transduction systems in Vibrio species. Future Microbiol 2011; 5:1403-12. [PMID: 20860484 DOI: 10.2217/fmb.10.90] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Studying the organization and conservation of the TonB systems across the genus Vibrio, we can tease out trends in gene arrangement and function that lead to clues about the evolution and necessity of the proteins in multiple TonB systems. The TonB2 systems, with additional TtpC proteins, are in general more promiscuous regarding their interactions with many different TonB-dependent transporters in the outer membrane. Studies show that the TtpC protein spans the periplasmic space, suggesting that it can be the connection between the energy from the proton motive force and the outer membrane protein receptors, which the shorter TonB2 cannot provide. As an earlier system, the combination of the TtpC protein and a TonB2 system must have been necessary for the function of the smaller TonB2 protein and to transduce energy in a medium that can have osmotic challenges.
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Affiliation(s)
- Carole J Kuehl
- Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, 97239, USA
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Morimoto YV, Nakamura S, Kami-ike N, Namba K, Minamino T. Charged residues in the cytoplasmic loop of MotA are required for stator assembly into the bacterial flagellar motor. Mol Microbiol 2010; 78:1117-29. [DOI: 10.1111/j.1365-2958.2010.07391.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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