1
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Johnson S, Deme JC, Furlong EJ, Caesar JJE, Chevance FFV, Hughes KT, Lea SM. Structural basis of directional switching by the bacterial flagellum. Nat Microbiol 2024; 9:1282-1292. [PMID: 38459206 DOI: 10.1038/s41564-024-01630-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 02/01/2024] [Indexed: 03/10/2024]
Abstract
The bacterial flagellum is a macromolecular protein complex that harvests energy from uni-directional ion flow across the inner membrane to power bacterial swimming via rotation of the flagellar filament. Rotation is bi-directional, with binding of a cytoplasmic chemotactic response regulator controlling reversal, though the structural and mechanistic bases for rotational switching are not well understood. Here we present cryoelectron microscopy structures of intact Salmonella flagellar basal bodies (3.2-5.5 Å), including the cytoplasmic C-ring complexes required for power transmission, in both counter-clockwise and clockwise rotational conformations. These reveal 180° movements of both the N- and C-terminal domains of the FliG protein, which, when combined with a high-resolution cryoelectron microscopy structure of the MotA5B2 stator, show that the stator shifts from the outside to the inside of the C-ring. This enables rotational switching and reveals how uni-directional ion flow across the inner membrane is used to accomplish bi-directional rotation of the flagellum.
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Affiliation(s)
- Steven Johnson
- Center for Structural Biology, CCR, NCI, Frederick, MD, USA.
| | - Justin C Deme
- Center for Structural Biology, CCR, NCI, Frederick, MD, USA
| | - Emily J Furlong
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
- Division of Biomedical Science and Biochemistry, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Joseph J E Caesar
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
- Central Oxford Structural Molecular Imaging Centre, University of Oxford, Oxford, UK
| | | | - Kelly T Hughes
- Department of Biology, University of Utah, Salt Lake City, UT, USA
| | - Susan M Lea
- Center for Structural Biology, CCR, NCI, Frederick, MD, USA.
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2
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Singh PK, Sharma P, Afanzar O, Goldfarb MH, Maklashina E, Eisenbach M, Cecchini G, Iverson TM. CryoEM structures reveal how the bacterial flagellum rotates and switches direction. Nat Microbiol 2024; 9:1271-1281. [PMID: 38632342 PMCID: PMC11087270 DOI: 10.1038/s41564-024-01674-1] [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: 08/19/2023] [Accepted: 03/12/2024] [Indexed: 04/19/2024]
Abstract
Bacterial chemotaxis requires bidirectional flagellar rotation at different rates. Rotation is driven by a flagellar motor, which is a supercomplex containing multiple rings. Architectural uncertainty regarding the cytoplasmic C-ring, or 'switch', limits our understanding of how the motor transmits torque and direction to the flagellar rod. Here we report cryogenic electron microscopy structures for Salmonella enterica serovar typhimurium inner membrane MS-ring and C-ring in a counterclockwise pose (4.0 Å) and isolated C-ring in a clockwise pose alone (4.6 Å) and bound to a regulator (5.9 Å). Conformational differences between rotational poses include a 180° shift in FliF/FliG domains that rotates the outward-facing MotA/B binding site to inward facing. The regulator has specificity for the clockwise pose by bridging elements unique to this conformation. We used these structures to propose how the switch reverses rotation and transmits torque to the flagellum, which advances the understanding of bacterial chemotaxis and bidirectional motor rotation.
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Affiliation(s)
- Prashant K Singh
- Department of Pharmacology, Vanderbilt University, Nashville, TN, USA
| | - Pankaj Sharma
- Department of Pharmacology, Vanderbilt University, Nashville, TN, USA
| | - Oshri Afanzar
- Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, CA, USA
| | - Margo H Goldfarb
- Department of Pharmacology, Vanderbilt University, Nashville, TN, USA
| | - Elena Maklashina
- Molecular Biology Division, San Francisco VA Health Care System, San Francisco, CA, USA
- Department of Biochemistry & Biophysics, University of California, San Francisco, CA, USA
| | - Michael Eisenbach
- Department of Biomolecular Sciences, The Weizmann Institute of Science, Rehovot, Israel
| | - Gary Cecchini
- Molecular Biology Division, San Francisco VA Health Care System, San Francisco, CA, USA
- Department of Biochemistry & Biophysics, University of California, San Francisco, CA, USA
| | - T M Iverson
- Department of Pharmacology, Vanderbilt University, Nashville, TN, USA.
- Department of Biochemistry, Vanderbilt University, Nashville, TN, USA.
- Center for Structural Biology, Vanderbilt University, Nashville, TN, USA.
- Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN, USA.
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3
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Wimmi S, Balinovic A, Brianceau C, Pintor K, Vielhauer J, Turkowyd B, Helbig C, Fleck M, Langenfeld K, Kahnt J, Glatter T, Endesfelder U, Diepold A. Cytosolic sorting platform complexes shuttle type III secretion system effectors to the injectisome in Yersinia enterocolitica. Nat Microbiol 2024; 9:185-199. [PMID: 38172622 PMCID: PMC10769875 DOI: 10.1038/s41564-023-01545-1] [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: 09/23/2022] [Accepted: 11/06/2023] [Indexed: 01/05/2024]
Abstract
Bacteria use type III secretion injectisomes to inject effector proteins into eukaryotic target cells. Recruitment of effectors to the machinery and the resulting export hierarchy involve the sorting platform. These conserved proteins form pod structures at the cytosolic interface of the injectisome but are also mobile in the cytosol. Photoactivated localization microscopy in Yersinia enterocolitica revealed a direct interaction of the sorting platform proteins SctQ and SctL with effectors in the cytosol of live bacteria. These proteins form larger cytosolic protein complexes involving the ATPase SctN and the membrane connector SctK. The mobility and composition of these mobile pod structures are modulated in the presence of effectors and their chaperones, and upon initiation of secretion, which also increases the number of injectisomes from ~5 to ~18 per bacterium. Our quantitative data support an effector shuttling mechanism, in which sorting platform proteins bind to effectors in the cytosol and deliver the cargo to the export gate at the membrane-bound injectisome.
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Affiliation(s)
- Stephan Wimmi
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Alexander Balinovic
- Department of Systems and Synthetic Microbiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
- SYNMIKRO, Center for Synthetic Microbiology, Marburg, Germany
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA
- Institute for Microbiology and Biotechnology, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | - Corentin Brianceau
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Katherine Pintor
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Jan Vielhauer
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Bartosz Turkowyd
- Department of Systems and Synthetic Microbiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
- SYNMIKRO, Center for Synthetic Microbiology, Marburg, Germany
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA
- Institute for Microbiology and Biotechnology, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | - Carlos Helbig
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Moritz Fleck
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Katja Langenfeld
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Jörg Kahnt
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
- Mass Spectrometry and Proteomics Facility, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Timo Glatter
- Mass Spectrometry and Proteomics Facility, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Ulrike Endesfelder
- Department of Systems and Synthetic Microbiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
- SYNMIKRO, Center for Synthetic Microbiology, Marburg, Germany.
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA.
- Institute for Microbiology and Biotechnology, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany.
| | - Andreas Diepold
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
- SYNMIKRO, Center for Synthetic Microbiology, Marburg, Germany.
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4
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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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5
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Soto JE, Lara-Tejero M. The sorting platform in the type III secretion pathway: From assembly to function. Bioessays 2023; 45:e2300078. [PMID: 37329195 DOI: 10.1002/bies.202300078] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 06/05/2023] [Accepted: 06/07/2023] [Indexed: 06/18/2023]
Abstract
The type III secretion system (T3SS) is a specialized nanomachine that enables bacteria to secrete proteins in a specific order and directly deliver a specific set of them, collectively known as effectors, into eukaryotic organisms. The core structure of the T3SS is a syringe-like apparatus composed of multiple building blocks, including both membrane-associated and soluble proteins. The cytosolic components organize together in a chamber-like structure known as the sorting platform (SP), responsible for recruiting, sorting, and initiating the substrates destined to engage this secretion pathway. In this article, we provide an overview of recent findings on the SP's structure and function, with a particular focus on its assembly pathway. Furthermore, we discuss the molecular mechanisms behind the recruitment and hierarchical sorting of substrates by this cytosolic complex. Overall, the T3SS is a highly specialized and complex system that requires precise coordination to function properly. A deeper understanding of how the SP orchestrates T3S could enhance our comprehension of this complex nanomachine, which is central to the host-pathogen interface, and could aid in the development of novel strategies to fight bacterial infections.
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Affiliation(s)
- Jose Eduardo Soto
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut, USA
| | - María Lara-Tejero
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut, USA
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6
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Case HB, Gonzalez S, Gustafson ME, Dickenson NE. Differential regulation of Shigella Spa47 ATPase activity by a native C-terminal product of Spa33. Front Cell Infect Microbiol 2023; 13:1183211. [PMID: 37389216 PMCID: PMC10302723 DOI: 10.3389/fcimb.2023.1183211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 05/17/2023] [Indexed: 07/01/2023] Open
Abstract
Shigella is a Gram-negative bacterial pathogen that relies on a single type three secretion system (T3SS) as its primary virulence factor. The T3SS includes a highly conserved needle-like apparatus that directly injects bacterial effector proteins into host cells, subverting host cell function, initiating infection, and circumventing resulting host immune responses. Recent findings have located the T3SS ATPase Spa47 to the base of the Shigella T3SS apparatus and have correlated its catalytic function to apparatus formation, protein effector secretion, and overall pathogen virulence. This critical correlation makes Spa47 ATPase activity regulation a likely point of native control over Shigella virulence and a high interest target for non-antibiotic- based therapeutics. Here, we provide a detailed characterization of the natural 11.6 kDa C-terminal translation product of the Shigella T3SS protein Spa33 (Spa33C), showing that it is required for proper virulence and that it pulls down with several known T3SS proteins, consistent with a structural role within the sorting platform of the T3SS apparatus. In vitro binding assays and detailed kinetic analyses suggest an additional role, however, as Spa33C differentially regulates Spa47 ATPase activity based on Spa47s oligomeric state, downregulating Spa47 monomer activity and upregulating activity of both homo-oligomeric Spa47 and the hetero-oligomeric MxiN2Spa47 complex. These findings identify Spa33C as only the second known differential T3SS ATPase regulator to date, with the Shigella protein MxiN representing the other. Describing this differential regulatory protein pair begins to close an important gap in understanding of how Shigella may modulate virulence through Spa47 activity and T3SS function.
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Affiliation(s)
| | | | | | - Nicholas E. Dickenson
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT, United States
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7
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Tao A, Liu G, Zhang R, Yuan J. Precise Measurement of the Stoichiometry of the Adaptive Bacterial Flagellar Switch. mBio 2023; 14:e0018923. [PMID: 36946730 PMCID: PMC10128058 DOI: 10.1128/mbio.00189-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/23/2023] Open
Abstract
The cytoplasmic ring (C-ring) of the bacterial flagellar motor controls the motor rotation direction, thereby controlling bacterial run-and-tumble behavior. The C-ring has been shown to undergo adaptive remodeling in response to changes in motor directional bias. However, the stoichiometry and arrangement of the C-ring is still unclear due to contradiction between the results from fluorescence studies and cryo-electron microscopy (cryo-EM) structural analysis. Here, by using the copy number of FliG molecules (34) in the C-ring as a reference, we precisely measured the copy numbers of FliM molecules in motors rotating exclusively counterclockwise (CCW) and clockwise (CW). We surprisingly found that there are on average 45 and 58 FliM molecules in CW and CCW rotating motors, respectively, which are much higher than previous estimates. Our results suggested a new mechanism of C-ring adaptation, that is, extra FliM molecules could be bound to the primary C-ring with probability depending on the motor rotational direction. We further confirmed that all of the FliM molecules in the C-ring function in chemotaxis signaling transduction because all of them could be bound by the chemotactic response regulator CheY-P. Our measurements provided new insights into the structure and arrangement of the flagellar switch. IMPORTANCE The bacterial flagellar switch can undergo adaptive remodeling in response to changes in motor rotation direction, thereby shifting its operating point to match the output of the chemotaxis signaling pathway. However, it remains unclear how the flagellar switch accomplishes this adaptive remodeling. Here, via precise fluorescence studies, we measured the absolute copy numbers of the critical component in the switch for motors rotating counterclockwise and clockwise, obtaining much larger numbers than previous relative estimates. Our results suggested a new mechanism of adaptive remodeling of the flagellar switch and provided new insights for updating the conformation spread model of the switch.
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Affiliation(s)
- Antai Tao
- Department of Physics, University of Science and Technology of China, Hefei, Anhui, China
| | - Guangzhe Liu
- Wenzhou Institute, University of Chinese Academy of Science, Wenzhou, Zhejiang, P.R. China
- School of Engineering and Science, University of Chinese Academy of Science, Beijing, P.R. China
| | - Rongjing Zhang
- Department of Physics, University of Science and Technology of China, Hefei, Anhui, China
| | - Junhua Yuan
- Department of Physics, University of Science and Technology of China, Hefei, Anhui, China
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8
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Toward a Shigella Vaccine: Opportunities and Challenges to Fight an Antimicrobial-Resistant Pathogen. Int J Mol Sci 2023; 24:ijms24054649. [PMID: 36902092 PMCID: PMC10003550 DOI: 10.3390/ijms24054649] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 02/23/2023] [Accepted: 02/24/2023] [Indexed: 03/04/2023] Open
Abstract
Shigellosis causes more than 200,000 deaths worldwide and most of this burden falls on Low- and Middle-Income Countries (LMICs), with a particular incidence in children under 5 years of age. In the last decades, Shigella has become even more worrisome because of the onset of antimicrobial-resistant strains (AMR). Indeed, the WHO has listed Shigella as one of the priority pathogens for the development of new interventions. To date, there are no broadly available vaccines against shigellosis, but several candidates are being evaluated in preclinical and clinical studies, bringing to light very important data and information. With the aim to facilitate the understanding of the state-of-the-art of Shigella vaccine development, here we report what is known about Shigella epidemiology and pathogenesis with a focus on virulence factors and potential antigens for vaccine development. We discuss immunity after natural infection and immunization. In addition, we highlight the main characteristics of the different technologies that have been applied for the development of a vaccine with broad protection against Shigella.
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9
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Prindle JR, Wang Y, Rocha JM, Diepold A, Gahlmann A. Distinct Cytosolic Complexes Containing the Type III Secretion System ATPase Resolved by Three-Dimensional Single-Molecule Tracking in Live Yersinia enterocolitica. Microbiol Spectr 2022; 10:e0174422. [PMID: 36354362 PMCID: PMC9769973 DOI: 10.1128/spectrum.01744-22] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 10/20/2022] [Indexed: 11/12/2022] Open
Abstract
The membrane-embedded injectisome, the structural component of the virulence-associated type III secretion system (T3SS), is used by Gram-negative bacterial pathogens to inject species-specific effector proteins into eukaryotic host cells. The cytosolic injectisome proteins are required for export of effectors and display both stationary, injectisome-bound populations and freely diffusing cytosolic populations. How the cytosolic injectisome proteins interact with each other in the cytosol and associate with membrane-embedded injectisomes remains unclear. Here, we utilized three-dimensional (3D) single-molecule tracking to resolve distinct cytosolic complexes of injectisome proteins in living Yersinia enterocolitica cells. Tracking of the enhanced yellow fluorescent protein (eYFP)-labeled ATPase YeSctN and its regulator, YeSctL, revealed that these proteins form a cytosolic complex with each other and then further with YeSctQ. YeSctNL and YeSctNLQ complexes can be observed both in wild-type cells and in ΔsctD mutants, which cannot assemble injectisomes. In ΔsctQ mutants, the relative abundance of the YeSctNL complex is considerably increased. These data indicate that distinct cytosolic complexes of injectisome proteins can form prior to injectisome binding, which has important implications for how injectisomes are functionally regulated. IMPORTANCE Injectisomes are membrane-embedded, multiprotein assemblies used by bacterial pathogens to inject virulent effector proteins into eukaryotic host cells. Protein secretion is regulated by cytosolic proteins that dynamically bind and unbind at injectisomes. However, how these regulatory proteins interact with each other remains unknown. By measuring the diffusion rates of single molecules in living cells, we show that cytosolic injectisome proteins form distinct oligomeric complexes with each other prior to binding to injectisomes. We additionally identify the molecular compositions of these complexes and quantify their relative abundances. Quantifying to what extent cytosolic proteins exist as part of larger complexes in living cells has important implications for deciphering the complexity of biomolecular mechanisms. The results and methods reported here are thus relevant for advancing our understanding of how injectisomes and related multiprotein assemblies, such as bacterial flagellar motors, are functionally regulated.
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Affiliation(s)
- Joshua R. Prindle
- Department of Chemistry, University of Virginia, Charlottesville, Virginia, USA
| | - Yibo Wang
- Department of Chemistry, University of Virginia, Charlottesville, Virginia, USA
| | - Julian M. Rocha
- Department of Chemistry, University of Virginia, Charlottesville, Virginia, USA
| | - Andreas Diepold
- Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Andreas Gahlmann
- Department of Chemistry, University of Virginia, Charlottesville, Virginia, USA
- Department of Molecular Physiology & Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia, USA
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10
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Guo S, Liu J. The Bacterial Flagellar Motor: Insights Into Torque Generation, Rotational Switching, and Mechanosensing. Front Microbiol 2022; 13:911114. [PMID: 35711788 PMCID: PMC9195833 DOI: 10.3389/fmicb.2022.911114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2022] [Accepted: 05/06/2022] [Indexed: 11/18/2022] Open
Abstract
The flagellar motor is a bidirectional rotary nanomachine used by many bacteria to sense and move through environments of varying complexity. The bidirectional rotation of the motor is governed by interactions between the inner membrane-associated stator units and the C-ring in the cytoplasm. In this review, we take a structural biology perspective to discuss the distinct conformations of the stator complex and the C-ring that regulate bacterial motility by switching rotational direction between the clockwise (CW) and counterclockwise (CCW) senses. We further contextualize recent in situ structural insights into the modulation of the stator units by accessory proteins, such as FliL, to generate full torque. The dynamic structural remodeling of the C-ring and stator complexes as well as their association with signaling and accessory molecules provide a mechanistic basis for how bacteria adjust motility to sense, move through, and survive in specific niches both outside and within host cells and tissues.
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Affiliation(s)
- Shuaiqi Guo
- Microbial Sciences Institute, Yale University, West Haven, CT, United States.,Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT, United States
| | - Jun Liu
- Microbial Sciences Institute, Yale University, West Haven, CT, United States.,Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT, United States
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11
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Abstract
The bacterial flagellum is a large macromolecular assembly that acts as propeller, providing motility through the rotation of a long extracellular filament. It is composed of over 20 different proteins, many of them highly oligomeric. Accordingly, it has attracted a huge amount of interest amongst researchers and the wider public alike. Nonetheless, most of its molecular details had long remained elusive.This however has changed recently, with the emergence of cryo-EM to determine the structure of protein assemblies at near-atomic resolution. Within a few years, the atomic details of most of the flagellar components have been elucidated, revealing not only its overall architecture but also the molecular details of its rotation mechanism. However, many questions remained unaddressed, notably on the complexity of the assembly of such an intricate machinery.In this chapter, we review the current state of our understanding of the bacterial flagellum structure, focusing on the recent development from cryo-EM. We also highlight the various elements that still remain to be fully characterized. Finally, we summarize the existing model for flagellum assembly and discuss some of the outstanding questions that are still pending in our understanding of the diversity of assembly pathways.
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Affiliation(s)
- Natalie S Al-Otaibi
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, UK
| | - Julien R C Bergeron
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, UK.
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12
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Rudden LSP, Musson SC, Benesch JLP, Degiacomi MT. Biobox: a toolbox for biomolecular modelling. Bioinformatics 2021; 38:1149-1151. [PMID: 34791029 PMCID: PMC8796382 DOI: 10.1093/bioinformatics/btab785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 10/15/2021] [Accepted: 11/11/2021] [Indexed: 02/05/2023] Open
Abstract
MOTIVATION The implementation of biomolecular modelling methods and analyses can be cumbersome, often carried out with in-house software reimplementing common tasks, and requiring the integration of diverse software libraries. RESULTS We present Biobox, a Python-based toolbox facilitating the implementation of biomolecular modelling methods. AVAILABILITY AND IMPLEMENTATION Biobox is freely available on https://github.com/degiacom/biobox, along with its API and interactive Jupyter notebook tutorials.
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Affiliation(s)
| | | | - Justin L P Benesch
- Department of Chemistry, Biochemistry Building, University of Oxford, Oxford OX1 3QU, UK
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13
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Otten C, Seifert T, Hausner J, Büttner D. The Contribution of the Predicted Sorting Platform Component HrcQ to Type III Secretion in Xanthomonas campestris pv. vesicatoria Depends on an Internal Translation Start Site. Front Microbiol 2021; 12:752733. [PMID: 34721356 PMCID: PMC8553256 DOI: 10.3389/fmicb.2021.752733] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 09/22/2021] [Indexed: 11/13/2022] Open
Abstract
Pathogenicity of the Gram-negative bacterium Xanthomonas campestris pv. vesicatoria depends on a type III secretion (T3S) system which translocates effector proteins into plant cells. T3S systems are conserved in plant- and animal-pathogenic bacteria and consist of at least nine structural core components, which are designated Sct (secretion and cellular translocation) in animal-pathogenic bacteria. Sct proteins are involved in the assembly of the membrane-spanning secretion apparatus which is associated with an extracellular needle structure and a cytoplasmic sorting platform. Components of the sorting platform include the ATPase SctN, its regulator SctL, and pod-like structures at the periphery of the sorting platform consisting of SctQ proteins. Members of the SctQ family form a complex with the C-terminal protein domain, SctQC, which is translated as separate protein and likely acts either as a structural component of the sorting platform or as a chaperone for SctQ. The sorting platform has been intensively studied in animal-pathogenic bacteria but has not yet been visualized in plant pathogens. We previously showed that the SctQ homolog HrcQ from X. campestris pv. vesicatoria assembles into complexes which associate with the T3S system and interact with components of the ATPase complex. Here, we report the presence of an internal alternative translation start site in hrcQ leading to the separate synthesis of the C-terminal protein region (HrcQC). The analysis of genomic hrcQ mutants showed that HrcQC is essential for pathogenicity and T3S. Increased expression levels of hrcQ or the T3S genes, however, compensated the lack of HrcQC. Interaction studies and protein analyses suggest that HrcQC forms a complex with HrcQ and promotes HrcQ stability. Furthermore, HrcQC colocalizes with HrcQ as was shown by fluorescence microscopy, suggesting that it is part of the predicted cytoplasmic sorting platform. In agreement with this finding, HrcQC interacts with the inner membrane ring protein HrcD and the SctK-like linker protein HrpB4 which contributes to the docking of the HrcQ complex to the membrane-spanning T3S apparatus. Taken together, our data suggest that HrcQC acts as a chaperone for HrcQ and as a structural component of the predicted sorting platform.
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Affiliation(s)
- Christian Otten
- Department of Genetics, Institute for Biology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Tanja Seifert
- Department of Genetics, Institute for Biology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Jens Hausner
- Department of Genetics, Institute for Biology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Daniela Büttner
- Department of Genetics, Institute for Biology, Martin Luther University Halle-Wittenberg, Halle, Germany
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14
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Takekawa N, Nishikino T, Yamashita T, Hori K, Onoue Y, Ihara K, Kojima S, Homma M, Imada K. A slight bending of an α-helix in FliM creates a counterclockwise-locked structure of the flagellar motor in Vibrio. J Biochem 2021; 170:531-538. [PMID: 34143212 DOI: 10.1093/jb/mvab074] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2021] [Accepted: 06/01/2021] [Indexed: 11/13/2022] Open
Abstract
Many bacteria swim by rotating flagella. The chemotaxis system controls the direction of flagellar rotation. Vibrio alginolyticus, which has a single polar flagellum, swims smoothly by rotating the flagellar motor counterclockwise (CCW) in response to attractants. In response to repellents, the motor frequently switches its rotational direction between CCW and clockwise (CW). We isolated a mutant strain that swims with a CW-locked rotation of the flagellum, which pulls rather than pushes the cell. This CW phenotype arises from a R49P substitution in FliM, which is the component in the C-ring of the motor that binds the chemotaxis signaling protein, phosphorylated CheY. However, this phenotype is independent of CheY, indicating that the mutation produces a CW conformation of the C-ring in the absence of CheY. The crystal structure of FliM with the R49P substitution showed a conformational change in the N-terminal α-helix of the middle domain of FliM (FliMM). This helix should mediates FliM-FliM interaction. The structural models of wild-type and mutant C-ring showed that the relatively small conformational change in FliMM induces a drastic rearrangement of the conformation of the FliMM domain that generates a CW conformation of the C-ring.
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Affiliation(s)
- Norihiro Takekawa
- Department of Macromolecular Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Tatsuro Nishikino
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan.,Research Center for Next-Generation Protein Sciences, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Toshiki Yamashita
- Department of Macromolecular Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Kiyoshiro Hori
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
| | - Yasuhiro Onoue
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
| | - Kunio Ihara
- Center for Gene Research, Nagoya University, Furocho, Nagoya, Aichi 464-8602, Japan
| | - Seiji Kojima
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
| | - Michio Homma
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
| | - Katsumi Imada
- Department of Macromolecular Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
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15
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Tachiyama S, Skaar R, Chang Y, Carroll BL, Muthuramalingam M, Whittier SK, Barta ML, Picking WL, Liu J, Picking WD. Composition and Biophysical Properties of the Sorting Platform Pods in the Shigella Type III Secretion System. Front Cell Infect Microbiol 2021; 11:682635. [PMID: 34150677 PMCID: PMC8211105 DOI: 10.3389/fcimb.2021.682635] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Accepted: 05/17/2021] [Indexed: 01/28/2023] Open
Abstract
Shigella flexneri, causative agent of bacillary dysentery (shigellosis), uses a type III secretion system (T3SS) as its primary virulence factor. The T3SS injectisome delivers effector proteins into host cells to promote entry and create an important intracellular niche. The injectisome's cytoplasmic sorting platform (SP) is a critical assembly that contributes to substrate selection and energizing secretion. The SP consists of oligomeric Spa33 "pods" that associate with the basal body via MxiK and connect to the Spa47 ATPase via MxiN. The pods contain heterotrimers of Spa33 with one full-length copy associated with two copies of a C-terminal domain (Spa33C). The structure of Spa33C is known, but the precise makeup and structure of the pods in situ remains elusive. We show here that recombinant wild-type Spa33 can be prepared as a heterotrimer that forms distinct stable complexes with MxiK and MxiN. In two-hybrid analyses, association of the Spa33 complex with these proteins occurs via the full-length Spa33 component. Furthermore, these complexes each have distinct biophysical properties. Based on these properties, new high-resolution cryo-electron tomography data and architectural similarities between the Spa33 and flagellar FliM-FliN complexes, we provide a preliminary model of the Spa33 heterotrimers within the SP pods. From these findings and evolving models of SP interfaces and dynamics in the Yersinia and Salmonella T3SS, we suggest a model for SP function in which two distinct complexes come together within the context of the SP to contribute to form the complete pod structures during the recruitment of T3SS secretion substrates.
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Affiliation(s)
- Shoichi Tachiyama
- Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS, United States,Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, United States,Microbial Sciences Institute, Yale University, West Haven, CT, United States
| | - Ryan Skaar
- Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS, United States
| | - Yunjie Chang
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, United States,Microbial Sciences Institute, Yale University, West Haven, CT, United States
| | - Brittany L. Carroll
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, United States,Microbial Sciences Institute, Yale University, West Haven, CT, United States
| | | | - Sean K. Whittier
- Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS, United States
| | - Michael L. Barta
- Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS, United States
| | - Wendy L. Picking
- Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS, United States
| | - Jun Liu
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, United States,Microbial Sciences Institute, Yale University, West Haven, CT, United States
| | - William D. Picking
- Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, KS, United States,*Correspondence: William D. Picking,
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16
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Chang Y, Carroll BL, Liu J. Structural basis of bacterial flagellar motor rotation and switching. Trends Microbiol 2021; 29:1024-1033. [PMID: 33865677 DOI: 10.1016/j.tim.2021.03.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2021] [Revised: 03/11/2021] [Accepted: 03/16/2021] [Indexed: 01/08/2023]
Abstract
The bacterial flagellar motor, a remarkable rotary machine, can rapidly switch between counterclockwise (CCW) and clockwise (CW) rotational directions to control the migration behavior of the bacterial cell. The flagellar motor consists of a bidirectional spinning rotor surrounded by torque-generating stator units. Recent high-resolution in vitro and in situ structural studies have revealed stunning details of the individual components of the flagellar motor and their interactions in both the CCW and CW senses. In this review, we discuss these structures and their implications for understanding the molecular mechanisms underlying flagellar rotation and switching.
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Affiliation(s)
- Yunjie Chang
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06536, USA; Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Brittany L Carroll
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06536, USA; Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Jun Liu
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06536, USA; Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA.
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17
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The Shigella Type III Secretion System: An Overview from Top to Bottom. Microorganisms 2021; 9:microorganisms9020451. [PMID: 33671545 PMCID: PMC7926512 DOI: 10.3390/microorganisms9020451] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 02/16/2021] [Accepted: 02/18/2021] [Indexed: 12/16/2022] Open
Abstract
Shigella comprises four species of human-restricted pathogens causing bacillary dysentery. While Shigella possesses multiple genetic loci contributing to virulence, a type III secretion system (T3SS) is its primary virulence factor. The Shigella T3SS nanomachine consists of four major assemblies: the cytoplasmic sorting platform; the envelope-spanning core/basal body; an exposed needle; and a needle-associated tip complex with associated translocon that is inserted into host cell membranes. The initial subversion of host cell activities is carried out by the effector functions of the invasion plasmid antigen (Ipa) translocator proteins, with the cell ultimately being controlled by dedicated effector proteins that are injected into the host cytoplasm though the translocon. Much of the information now available on the T3SS injectisome has been accumulated through collective studies on the T3SS from three systems, those of Shigella flexneri, Salmonella typhimurium and Yersinia enterocolitica/Yersinia pestis. In this review, we will touch upon the important features of the T3SS injectisome that have come to light because of research in the Shigella and closely related systems. We will also briefly highlight some of the strategies being considered to target the Shigella T3SS for disease prevention.
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18
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Structure of the Yersinia injectisome in intracellular host cell phagosomes revealed by cryo FIB electron tomography. J Struct Biol 2021; 213:107701. [PMID: 33549695 DOI: 10.1016/j.jsb.2021.107701] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 12/17/2020] [Accepted: 01/14/2021] [Indexed: 02/03/2023]
Abstract
Many pathogenic bacteria use the type III secretion system (T3SS), or injectisome, to secrete toxins into host cells. These protruding systems are primary targets for drug and vaccine development. Upon contact between injectisomes and host membranes, toxin secretion is triggered. How this works structurally and functionally is yet unknown. Using cryo-focused ion beam milling and cryo-electron tomography, we visualized injectisomes of Yersinia enterocolitica inside the phagosomes of infected human myeloid cells in a close-to-native state. We observed that a minimum needle length is required for injectisomes to contact the host membrane and bending of host membranes by some injectisomes that contact the host. Through subtomogram averaging, the structure of the entire injectisome was determined, which revealed structural differences in the cytosolic sorting platform compared to other bacteria. These findings contribute to understanding how injectisomes secrete toxins into host cells and provides the indispensable native context. The application of these cryo-electron microscopy techniques paves the way for the study of the 3D structure of infection-relevant protein complexes in host-pathogen interactions.
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19
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Milne-Davies B, Wimmi S, Diepold A. Adaptivity and dynamics in type III secretion systems. Mol Microbiol 2020; 115:395-411. [PMID: 33251695 DOI: 10.1111/mmi.14658] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 11/17/2020] [Accepted: 11/23/2020] [Indexed: 01/07/2023]
Abstract
The type III secretion system is the common core of two bacterial molecular machines: the flagellum and the injectisome. The flagellum is the most widely distributed prokaryotic locomotion device, whereas the injectisome is a syringe-like apparatus for inter-kingdom protein translocation, which is essential for virulence in important human pathogens. The successful concept of the type III secretion system has been modified for different bacterial needs. It can be adapted to changing conditions, and was found to be a dynamic complex constantly exchanging components. In this review, we highlight the flexibility, adaptivity, and dynamic nature of the type III secretion system.
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Affiliation(s)
- Bailey Milne-Davies
- Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Marburg, Germany
| | - Stephan Wimmi
- Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Marburg, Germany
| | - Andreas Diepold
- Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Marburg, Germany
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20
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Bajunaid W, Haidar-Ahmad N, Kottarampatel AH, Ourida Manigat F, Silué N, F. Tchagang C, Tomaro K, Campbell-Valois FX. The T3SS of Shigella: Expression, Structure, Function, and Role in Vacuole Escape. Microorganisms 2020; 8:microorganisms8121933. [PMID: 33291504 PMCID: PMC7762205 DOI: 10.3390/microorganisms8121933] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 12/01/2020] [Accepted: 12/03/2020] [Indexed: 12/18/2022] Open
Abstract
Shigella spp. are one of the leading causes of infectious diarrheal diseases. They are Escherichia coli pathovars that are characterized by the harboring of a large plasmid that encodes most virulence genes, including a type III secretion system (T3SS). The archetypal element of the T3SS is the injectisome, a syringe-like nanomachine composed of approximately 20 proteins, spanning both bacterial membranes and the cell wall, and topped with a needle. Upon contact of the tip of the needle with the plasma membrane, the injectisome secretes its protein substrates into host cells. Some of these substrates act as translocators or effectors whose functions are key to the invasion of the cytosol and the cell-to-cell spread characterizing the lifestyle of Shigella spp. Here, we review the structure, assembly, function, and methods to measure the activity of the injectisome with a focus on Shigella, but complemented with data from other T3SS if required. We also present the regulatory cascade that controls the expression of T3SS genes in Shigella. Finally, we describe the function of translocators and effectors during cell-to-cell spread, particularly during escape from the vacuole, a key element of Shigella’s pathogenesis that has yet to reveal all of its secrets.
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Affiliation(s)
- Waad Bajunaid
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (W.B.); (N.H.-A.); (A.H.K.); (F.O.M.); (N.S.); (C.F.T.); (K.T.)
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
| | - Nathaline Haidar-Ahmad
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (W.B.); (N.H.-A.); (A.H.K.); (F.O.M.); (N.S.); (C.F.T.); (K.T.)
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
| | - Anwer Hasil Kottarampatel
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (W.B.); (N.H.-A.); (A.H.K.); (F.O.M.); (N.S.); (C.F.T.); (K.T.)
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
| | - France Ourida Manigat
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (W.B.); (N.H.-A.); (A.H.K.); (F.O.M.); (N.S.); (C.F.T.); (K.T.)
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
| | - Navoun Silué
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (W.B.); (N.H.-A.); (A.H.K.); (F.O.M.); (N.S.); (C.F.T.); (K.T.)
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
| | - Caetanie F. Tchagang
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (W.B.); (N.H.-A.); (A.H.K.); (F.O.M.); (N.S.); (C.F.T.); (K.T.)
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
| | - Kyle Tomaro
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (W.B.); (N.H.-A.); (A.H.K.); (F.O.M.); (N.S.); (C.F.T.); (K.T.)
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
| | - François-Xavier Campbell-Valois
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (W.B.); (N.H.-A.); (A.H.K.); (F.O.M.); (N.S.); (C.F.T.); (K.T.)
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
- Correspondence:
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21
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Chang Y, Zhang K, Carroll BL, Zhao X, Charon NW, Norris SJ, Motaleb MA, Li C, Liu J. Molecular mechanism for rotational switching of the bacterial flagellar motor. Nat Struct Mol Biol 2020; 27:1041-1047. [PMID: 32895555 PMCID: PMC8129871 DOI: 10.1038/s41594-020-0497-2] [Citation(s) in RCA: 67] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Accepted: 08/03/2020] [Indexed: 12/20/2022]
Abstract
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.
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Affiliation(s)
- Yunjie Chang
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06516, USA,Microbial Sciences Institute, Yale University, West Haven, CT 06536, USA
| | - Kai Zhang
- Philips Institute for Oral Health Research, Virginia Commonwealth University, Richmond, VA 23298, USA
| | - Brittany L. Carroll
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06516, USA,Microbial Sciences Institute, Yale University, West Haven, CT 06536, USA
| | - Xiaowei Zhao
- Department of Pathology and Laboratory Medicine, University of Texas Health Science Center, Houston, TX 77030, USA,Current address: Howard Hughes Medical Institute, Janelia Research Campus, Ashburn, VA 20147, USA
| | - Nyles W. Charon
- Department of Microbiology, Immunology, and Cell Biology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, USA
| | - Steven J. Norris
- Department of Pathology and Laboratory Medicine, University of Texas Health Science Center, Houston, TX 77030, USA
| | - Md A Motaleb
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC 27834, USA
| | - Chunhao Li
- Philips Institute for Oral Health Research, Virginia Commonwealth University, Richmond, VA, USA.
| | - Jun Liu
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA. .,Microbial Sciences Institute, Yale University, West Haven, CT, USA.
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22
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Structural Conservation and Adaptation of the Bacterial Flagella Motor. Biomolecules 2020; 10:biom10111492. [PMID: 33138111 PMCID: PMC7693769 DOI: 10.3390/biom10111492] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 10/26/2020] [Accepted: 10/27/2020] [Indexed: 02/07/2023] Open
Abstract
Many bacteria require flagella for the ability to move, survive, and cause infection. The flagellum is a complex nanomachine that has evolved to increase the fitness of each bacterium to diverse environments. Over several decades, molecular, biochemical, and structural insights into the flagella have led to a comprehensive understanding of the structure and function of this fascinating nanomachine. Notably, X-ray crystallography, cryo-electron microscopy (cryo-EM), and cryo-electron tomography (cryo-ET) have elucidated the flagella and their components to unprecedented resolution, gleaning insights into their structural conservation and adaptation. In this review, we focus on recent structural studies that have led to a mechanistic understanding of flagellar assembly, function, and evolution.
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23
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Abstract
The bacterial flagellar motor is the most complex structure in the bacterial cell, driving the ion-driven rotation of the helical flagellum. The ordered expression of the regulon and the assembly of the series of interacting protein rings, spanning the inner and outer membranes to form the ∼45–50-nm protein complex, have made investigation of the structure and mechanism a major challenge since its recognition as a rotating nanomachine about 40 years ago. Painstaking molecular genetics, biochemistry, and electron microscopy revealed a tiny electric motor spinning in the bacterial membrane. Over the last decade, new single-molecule and in vivo biophysical methods have allowed investigation of the stability of this and other large protein complexes, working in their natural environment inside live cells. This has revealed that in the bacterial flagellar motor, protein molecules in both the rotor and stator exchange with freely circulating pools of spares on a timescale of minutes, even while motors are continuously rotating. This constant exchange has allowed the evolution of modified components allowing bacteria to keep swimming as the viscosity or the ion composition of the outside environment changes.
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Affiliation(s)
- Judith P. Armitage
- Department of Biochemistry, University of Oxford, OX1 3QU, United Kingdom
| | - Richard M. Berry
- Department of Physics, University of Oxford, OX1 3PU, United Kingdom
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24
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Carroll BL, Nishikino T, Guo W, Zhu S, Kojima S, Homma M, Liu J. The flagellar motor of Vibrio alginolyticus undergoes major structural remodeling during rotational switching. eLife 2020; 9:61446. [PMID: 32893817 PMCID: PMC7505661 DOI: 10.7554/elife.61446] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Accepted: 09/04/2020] [Indexed: 11/26/2022] Open
Abstract
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.
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Affiliation(s)
- 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
| | - Seiji Kojima
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan
| | - Michio Homma
- Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan
| | - Jun Liu
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, United States.,Microbial Sciences Institute, Yale University, West Haven, United States
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25
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Structure and Energy-Conversion Mechanism of the Bacterial Na+-Driven Flagellar Motor. Trends Microbiol 2020; 28:719-731. [DOI: 10.1016/j.tim.2020.03.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 03/16/2020] [Accepted: 03/25/2020] [Indexed: 01/09/2023]
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26
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Khan S. The Architectural Dynamics of the Bacterial Flagellar Motor Switch. Biomolecules 2020; 10:E833. [PMID: 32486003 PMCID: PMC7355467 DOI: 10.3390/biom10060833] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 05/23/2020] [Accepted: 05/25/2020] [Indexed: 02/06/2023] Open
Abstract
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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Affiliation(s)
- Shahid Khan
- Molecular Biology Consortium, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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27
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Beeby M, Ferreira JL, Tripp P, Albers SV, Mitchell DR. Propulsive nanomachines: the convergent evolution of archaella, flagella and cilia. FEMS Microbiol Rev 2020; 44:253-304. [DOI: 10.1093/femsre/fuaa006] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 03/06/2020] [Indexed: 02/06/2023] Open
Abstract
ABSTRACT
Echoing the repeated convergent evolution of flight and vision in large eukaryotes, propulsive swimming motility has evolved independently in microbes in each of the three domains of life. Filamentous appendages – archaella in Archaea, flagella in Bacteria and cilia in Eukaryotes – wave, whip or rotate to propel microbes, overcoming diffusion and enabling colonization of new environments. The implementations of the three propulsive nanomachines are distinct, however: archaella and flagella rotate, while cilia beat or wave; flagella and cilia assemble at their tips, while archaella assemble at their base; archaella and cilia use ATP for motility, while flagella use ion-motive force. These underlying differences reflect the tinkering required to evolve a molecular machine, in which pre-existing machines in the appropriate contexts were iteratively co-opted for new functions and whose origins are reflected in their resultant mechanisms. Contemporary homologies suggest that archaella evolved from a non-rotary pilus, flagella from a non-rotary appendage or secretion system, and cilia from a passive sensory structure. Here, we review the structure, assembly, mechanism and homologies of the three distinct solutions as a foundation to better understand how propulsive nanomachines evolved three times independently and to highlight principles of molecular evolution.
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Affiliation(s)
- Morgan Beeby
- Department of Life Sciences, Frankland Road, Imperial College of London, London, SW7 2AZ, UK
| | - Josie L Ferreira
- Department of Life Sciences, Frankland Road, Imperial College of London, London, SW7 2AZ, UK
| | - Patrick Tripp
- Molecular Biology of Archaea, Institute of Biology, University of Freiburg, Schaenzlestrasse 1, 79211 Freiburg, Germany
| | - Sonja-Verena Albers
- Molecular Biology of Archaea, Institute of Biology, University of Freiburg, Schaenzlestrasse 1, 79211 Freiburg, Germany
| | - David R Mitchell
- Department of Cell and Developmental Biology, SUNY Upstate Medical University, 750 E. Adams St., Syracuse, NY 13210, USA
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Henderson LD, Matthews-Palmer TRS, Gulbronson CJ, Ribardo DA, Beeby M, Hendrixson DR. Diversification of Campylobacter jejuni Flagellar C-Ring Composition Impacts Its Structure and Function in Motility, Flagellar Assembly, and Cellular Processes. mBio 2020; 11:e02286-19. [PMID: 31911488 PMCID: PMC6946799 DOI: 10.1128/mbio.02286-19] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 11/19/2019] [Indexed: 12/22/2022] Open
Abstract
Bacterial flagella are reversible rotary motors that rotate external filaments for bacterial propulsion. Some flagellar motors have diversified by recruiting additional components that influence torque and rotation, but little is known about the possible diversification and evolution of core motor components. The mechanistic core of flagella is the cytoplasmic C ring, which functions as a rotor, directional switch, and assembly platform for the flagellar type III secretion system (fT3SS) ATPase. The C ring is composed of a ring of FliG proteins and a helical ring of surface presentation of antigen (SPOA) domains from the switch proteins FliM and one of two usually mutually exclusive paralogs, FliN or FliY. We investigated the composition, architecture, and function of the C ring of Campylobacter jejuni, which encodes FliG, FliM, and both FliY and FliN by a variety of interrogative approaches. We discovered a diversified C. jejuni C ring containing FliG, FliM, and both FliY, which functions as a classical FliN-like protein for flagellar assembly, and FliN, which has neofunctionalized into a structural role. Specific protein interactions drive the formation of a more complex heterooligomeric C. jejuni C-ring structure. We discovered that this complex C ring has additional cellular functions in polarly localizing FlhG for numerical regulation of flagellar biogenesis and spatial regulation of division. Furthermore, mutation of the C. jejuni C ring revealed a T3SS that was less dependent on its ATPase complex for assembly than were other systems. Our results highlight considerable evolved flagellar diversity that impacts motor output, biogenesis, and cellular processes in different species.IMPORTANCE The conserved core of bacterial flagellar motors reflects a shared evolutionary history that preserves the mechanisms essential for flagellar assembly, rotation, and directional switching. In this work, we describe an expanded and diversified set of core components in the Campylobacter jejuni flagellar C ring, the mechanistic core of the motor. Our work provides insight into how usually conserved core components may have diversified by gene duplication, enabling a division of labor of the ancestral protein between the two new proteins, acquisition of new roles in flagellar assembly and motility, and expansion of the function of the flagellum beyond motility, including spatial regulation of cell division and numerical control of flagellar biogenesis in C. jejuni Our results highlight that relatively small changes, such as gene duplications, can have substantial ramifications on the cellular roles of a molecular machine.
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Affiliation(s)
- Louie D Henderson
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | | | - Connor J Gulbronson
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Deborah A Ribardo
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Morgan Beeby
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | - David R Hendrixson
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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Abstract
The independent naming of components of injectisome-type type III secretion systems in different bacterial species has resulted in considerable confusion, impeding accessibility of the literature and hindering communication between scientists of the same field. A unified nomenclature had been proposed by Hueck more than 20 years ago. It found little attention for many years, but usage was sparked again by recent reviews and an international type III secretion meeting in 2016. Here, we propose that the field consistently switches to an extended version of this nomenclature to be no longer lost in translation.
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Abstract
Cells from all three domains of life on Earth utilize motile macromolecular devices that protrude from the cell surface to generate forces that allow them to swim through fluid media. Research carried out on archaea during the past decade or so has led to the recognition that, despite their common function, the motility devices of the three domains display fundamental differences in their properties and ancestry, reflecting a striking example of convergent evolution. Thus, the flagella of bacteria and the archaella of archaea employ rotary filaments that assemble from distinct subunits that do not share a common ancestor and generate torque using energy derived from distinct fuel sources, namely chemiosmotic ion gradients and FlaI motor-catalyzed ATP hydrolysis, respectively. The cilia of eukaryotes, however, assemble via kinesin-2-driven intraflagellar transport and utilize microtubules and ATP-hydrolyzing dynein motors to beat in a variety of waveforms via a sliding filament mechanism. Here, with reference to current structural and mechanistic information about these organelles, we briefly compare the evolutionary origins, assembly and tactic motility of archaella, flagella and cilia.
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Affiliation(s)
- Shahid Khan
- Molecular Biology Consortium, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
| | - Jonathan M Scholey
- Department of Molecular and Cell Biology, University of California @ Davis, CA 95616, USA.
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Kadari M, Lakhloufi D, Delforge V, Imbault V, Communi D, Smeesters P, Botteaux A. Multiple proteins arising from a single gene: The role of the Spa33 variants in Shigella T3SS regulation. Microbiologyopen 2019; 8:e932. [PMID: 31517452 PMCID: PMC6925163 DOI: 10.1002/mbo3.932] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Revised: 08/14/2019] [Accepted: 08/16/2019] [Indexed: 12/12/2022] Open
Abstract
Shigella invasion and dissemination in intestinal epithelial cells relies on a type 3 secretion system (T3SS), which mediates translocation of virulence proteins into host cells. T3SSs are composed of three major parts: an extracellular needle, a basal body, and a cytoplasmic complex. Three categories of proteins are hierarchically secreted: (a) the needle components, (b) the translocator proteins which form a pore (translocon) inside the host cell membrane and (c) the effectors interfering with the host cell signaling pathways. In the absence of host cell contact, the T3SS is maintained in an “off” state by the presence of a tip complex. Secretion is activated by host cell contact which allows the release of a gatekeeper protein called MxiC. In this work, we have investigated the role of Spa33, a component of the cytoplasmic complex, in the regulation of secretion. The spa33 gene encodes a 33‐kDa protein and a smaller fragment of 12 kDa (Spa33C) which are both essential components of the cytoplasmic complex. We have shown that the spa33 gene gives rise to 5 fragments of various sizes. Among them, three are necessary for T3SS. Interestingly, we have shown that Spa33 is implicated in the regulation of secretion. Indeed, the mutation of a single residue in Spa33 induces an effector mutant phenotype, in which MxiC is sequestered. Moreover, we have shown a direct interaction between Spa33 and MxiC.
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Affiliation(s)
- Mahendar Kadari
- Laboratory of Molecular Bacteriology, Faculty of Medicine, Free University of Brussels, Brussels, Belgium
| | - Dalila Lakhloufi
- Laboratory of Molecular Bacteriology, Faculty of Medicine, Free University of Brussels, Brussels, Belgium
| | - Valérie Delforge
- Laboratory of Molecular Bacteriology, Faculty of Medicine, Free University of Brussels, Brussels, Belgium
| | - Virginie Imbault
- Mass Spectrometry and Proteomics Facility, IRIBHM, Faculty of Medicine, Free University of Brussels, Brussels, Belgium
| | - David Communi
- Mass Spectrometry and Proteomics Facility, IRIBHM, Faculty of Medicine, Free University of Brussels, Brussels, Belgium
| | - Pierre Smeesters
- Laboratory of Molecular Bacteriology, Faculty of Medicine, Free University of Brussels, Brussels, Belgium.,Department of Pediatrics, Academic Children Hospital Queen Fabiola, Université libre de Bruxelles, Brussels, Belgium.,Tropical disease Group, Murdoch Children's, Research Institute, Melbourne, Vic., Australia.,Center for International Child Health, University of Melbourne, Melbourne, Vic., Australia
| | - Anne Botteaux
- Laboratory of Molecular Bacteriology, Faculty of Medicine, Free University of Brussels, Brussels, Belgium
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Molecular Organization of Soluble Type III Secretion System Sorting Platform Complexes. J Mol Biol 2019; 431:3787-3803. [DOI: 10.1016/j.jmb.2019.07.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 06/11/2019] [Accepted: 07/01/2019] [Indexed: 12/20/2022]
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Singh N, Wagner S. Investigating the assembly of the bacterial type III secretion system injectisome by in vivo photocrosslinking. Int J Med Microbiol 2019; 309:151331. [DOI: 10.1016/j.ijmm.2019.151331] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 07/09/2019] [Accepted: 07/12/2019] [Indexed: 12/11/2022] Open
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Minamino T, Kinoshita M, Namba K. Directional Switching Mechanism of the Bacterial Flagellar Motor. Comput Struct Biotechnol J 2019; 17:1075-1081. [PMID: 31452860 PMCID: PMC6700473 DOI: 10.1016/j.csbj.2019.07.020] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Revised: 07/26/2019] [Accepted: 07/27/2019] [Indexed: 11/16/2022] Open
Abstract
Bacteria sense temporal changes in extracellular stimuli via sensory signal transducers and move by rotating flagella towards into a favorable environment for their survival. Each flagellum is a supramolecular motility machine consisting of a bi-directional rotary motor, a universal joint and a helical propeller. The signal transducers transmit environmental signals to the flagellar motor through a cytoplasmic chemotactic signaling pathway. The flagellar motor is composed of a rotor and multiple stator units, each of which acts as a transmembrane proton channel to conduct protons and exert force on the rotor. FliG, FliM and FliN form the C ring on the cytoplasmic face of the basal body MS ring made of the transmembrane protein FliF and act as the rotor. The C ring also serves as a switching device that enables the motor to spin in both counterclockwise (CCW) and clockwise (CW) directions. The phosphorylated form of the chemotactic signaling protein CheY binds to FliM and FliN to induce conformational changes of the C ring responsible for switching the direction of flagellar motor rotation from CCW to CW. In this mini-review, we will describe current understanding of the switching mechanism of the bacterial flagellar motor.
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Affiliation(s)
- Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadoaka, Suita, Osaka 565-0871, Japan
| | - Miki Kinoshita
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadoaka, Suita, Osaka 565-0871, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadoaka, Suita, Osaka 565-0871, Japan
- RIKEN Center for Biosystems Dynamic Research & Spring-8 Center, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
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Abstract
Type III protein secretion systems (T3SSs), or injectisomes, are multiprotein nanomachines present in many Gram-negative bacteria that have a sustained long-standing close relationship with a eukaryotic host. These secretion systems have evolved to modulate host cellular functions through the activity of the effector proteins they deliver. To reach their destination, T3SS effectors must cross the multibarrier bacterial envelope and the eukaryotic cell membrane. Passage through the bacterial envelope is mediated by the needle complex, a central component of T3SSs that expands both the inner and outer membranes of Gram-negative bacteria. A set of T3SS secreted proteins, known as translocators, form a channel in the eukaryotic plasma membrane through which the effector proteins are delivered to reach the host cell cytosol. While the effector proteins are tailored to the specific lifestyle of the bacterium that encodes them, the injectisome is conserved among the different T3SSs. The central role of T3SSs in pathogenesis and their high degree of conservation make them a desirable target for the development of antimicrobial therapies against several important bacterial pathogens.
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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: 174] [Impact Index Per Article: 34.8] [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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Organization of the Flagellar Switch Complex of Bacillus subtilis. J Bacteriol 2019; 201:JB.00626-18. [PMID: 30455280 DOI: 10.1128/jb.00626-18] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 11/14/2018] [Indexed: 01/12/2023] Open
Abstract
While the protein complex responsible for controlling the direction (clockwise [CW] or counterclockwise [CCW]) of flagellar rotation has been fairly well studied in Escherichia coli and Salmonella, less is known about the switch complex in Bacillus subtilis or other Gram-positive species. Two component proteins (FliG and FliM) are shared between E. coli and B. subtilis, but in place of the protein FliN found in E. coli, the B. subtilis complex contains the larger protein FliY. Notably, in B. subtilis the signaling protein CheY-phosphate induces a switch from CW to CCW rotation, opposite to its action in E. coli Here, we have examined the architecture and function of the switch complex in B. subtilis using targeted cross-linking, bacterial two-hybrid protein interaction experiments, and characterization of mutant phenotypes. In major respects, the B. subtilis switch complex appears to be organized similarly to that in E. coli The complex is organized around a ring built from the large middle domain of FliM; this ring supports an array of FliG subunits organized in a similar way to that of E. coli, with the FliG C-terminal domain functioning in the generation of torque via conserved charged residues. Key differences from E. coli involve the middle domain of FliY, which forms an additional, more outboard array, and the C-terminal domains of FliM and FliY, which are organized into both FliY homodimers and FliM heterodimers. Together, the results suggest that the CW and CCW conformational states are similar in the Gram-negative and Gram-positive switches but that CheY-phosphate drives oppositely directed movements in the two cases.IMPORTANCE Flagellar motility plays key roles in the survival of many bacteria and in the harmful action of many pathogens. Bacterial flagella rotate; the direction of flagellar rotation is controlled by a multisubunit protein complex termed the switch complex. This complex has been extensively studied in Gram-negative model species, but little is known about the complex in Bacillus subtilis or other Gram-positive species. Notably, the switch complex in Gram-positive species responds to its effector CheY-phosphate (CheY-P) by switching to CCW rotation, whereas in E. coli or Salmonella CheY-P acts in the opposite way, promoting CW rotation. In the work here, the architecture of the B. subtilis switch complex has been probed using cross-linking, protein interaction measurements, and mutational approaches. The results cast light on the organization of the complex and provide a framework for understanding the mechanism of flagellar direction control in B. subtilis and other Gram-positive species.
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Abstract
Genetic coding in bacteria largely operates via the "one gene-one protein" paradigm. However, the peculiarities of the mRNA structure, the versatility of the genetic code, and the dynamic nature of translation sometimes allow organisms to deviate from the standard rules of protein encoding. Bacteria can use several unorthodox modes of translation to express more than one protein from a single mRNA cistron. One such alternative path is the use of additional translation initiation sites within the gene. Proteins whose translation is initiated at different start sites within the same reading frame will differ in their N termini but will have identical C-terminal segments. On the other hand, alternative initiation of translation in a register different from the frame dictated by the primary start codon will yield a protein whose sequence is entirely different from the one encoded in the main frame. The use of internal mRNA codons as translation start sites is controlled by the nucleotide sequence and the mRNA folding. The proteins of the alternative proteome generated via the "genes-within-genes" strategy may carry important functions. In this review, we summarize the currently known examples of bacterial genes encoding more than one protein due to the utilization of additional translation start sites and discuss the known or proposed functions of the alternative polypeptides in relation to the main protein product of the gene. We also discuss recent proteome- and genome-wide approaches that will allow the discovery of novel translation initiation sites in a systematic fashion.
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Lara-Tejero M, Qin Z, Hu B, Butan C, Liu J, Galán JE. Role of SpaO in the assembly of the sorting platform of a Salmonella type III secretion system. PLoS Pathog 2019; 15:e1007565. [PMID: 30668610 PMCID: PMC6358110 DOI: 10.1371/journal.ppat.1007565] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 02/01/2019] [Accepted: 01/04/2019] [Indexed: 11/23/2022] Open
Abstract
Many bacterial pathogens and symbionts use type III secretion machines to interact with their hosts by injecting bacterial effector proteins into host target cells. A central component of this complex machine is the cytoplasmic sorting platform, which orchestrates the engagement and preparation of type III secreted proteins for their delivery to the needle complex, the substructure of the type III secretion system that mediates their passage through the bacterial envelope. The sorting platform is thought to be a dynamic structure whose components alternate between assembled and disassembled states. However, how this dynamic behavior is controlled is not understood. In S. Typhimurium a core component of the sorting platform is SpaO, which is synthesized in two tandemly translated products, a full length (SpaOL) and a short form (SpaOS) composed of the C-terminal 101 amino acids. Here we show that in the absence of SpaOS the assembly of the needle substructure of the needle complex, which requires a functional sorting platform, can still occur although with reduced efficiency. Consistent with this observation, in the absence of SpaOS secretion of effectors proteins, which requires a fully assembled injectisome, is only slightly compromised. In the absence of SpaOS we detect a significant number of fully assembled needle complexes that are not associated with fully assembled sorting platforms. We also find that although binding of SpaOL to SpaOS can be detected in the absence of other components of the sorting platform, this interaction is not detected in the context of a fully assembled sorting platform suggesting that SpaOS may not be a core structural component of the sorting platform. Consistent with this observation we find that SpaOS and OrgB, a component of the sorting platform, share the same binding surface on SpaOL. We conclude that SpaOS regulates the assembly of the sorting platform during type III secretion. Many pathogenic and symbiotic gram-negative bacteria utilize type III secretion systems to deliver bacterial proteins, known as effectors, directly into the host cell cytosol to promote their survival and the colonization of tissues. Type III secretion systems or injectisomes are large, multiprotein complexes composed of several substructures: the needle complex, a multiring structure with a protruding needle-like appendage anchored in the bacterial envelope; the export apparatus, a set of membrane proteins that form a gate in the inner-membrane for the passage of effector proteins; and the sorting platform, a large cytosolic complex that delivers the effectors to the needle complex in an orderly fashion. In this study, we characterize SpaO, the core component of the Salmonella Typhimurium sorting platform. The spaO gene encodes two simultaneously translated products, a full length protein (SpaOL) and a shorter product (SpaOS) encompassing the last 101 aa of the full length product. Here we find that in the absence of SpaOS, the sorting platform still forms and functions although slightly less efficiently than in the wild-type situation, and therefore we conclude that SpaOS is most likely not a central structural component of the sorting platform and may play a regulatory role during the cycles of assembly and disassembly that the sorting platform undergoes. In addition, we identify residues critical for the interaction between SpaOL and OrgB and SpaOL and SpaOS and conclude that those interactions might be mutually exclusive further supporting the idea that SpaOS may not be a core structural component of the sorting platform. N-terminal residues in SpaOL are shown to be critical for the formation of the sorting platform. Our findings provide insights into the sorting platform substructure, a highly conserved element in type III secretion systems and may contribute to the development of novel therapeutic avenues to fight infection.
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Affiliation(s)
- Maria Lara-Tejero
- Department of Microbial Pathogenesis Yale University School of Medicine, New haven, CT, United States of America
- * E-mail:
| | - Zhuan Qin
- Department of Microbial Pathogenesis Yale University School of Medicine, New haven, CT, United States of America
- Microbial Science Institute, Yale University School of Medicine, New haven, CT, United States of America
| | - Bo Hu
- Department of Microbiology and Molecular Genetics McGovern Medical School, The University of Texas Health Science Center at Houston, TX, United States of America
- Pathology and Laboratory Medicine, McGovern Medical School, The University of Texas Health Science Center at Houston, TX, United States of America
| | - Carmen Butan
- Department of Microbial Pathogenesis Yale University School of Medicine, New haven, CT, United States of America
| | - Jun Liu
- Department of Microbial Pathogenesis Yale University School of Medicine, New haven, CT, United States of America
- Microbial Science Institute, Yale University School of Medicine, New haven, CT, United States of America
| | - Jorge E. Galán
- Department of Microbial Pathogenesis Yale University School of Medicine, New haven, CT, United States of America
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Diepold A. Assembly and Post-assembly Turnover and Dynamics in the Type III Secretion System. Curr Top Microbiol Immunol 2019; 427:35-66. [PMID: 31218503 DOI: 10.1007/82_2019_164] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The type III secretion system (T3SS) is one of the largest transmembrane complexes in bacteria, comprising several intricately linked and embedded substructures. The assembly of this nanomachine is a hierarchical process which is regulated and controlled by internal and external cues at several critical points. Recently, it has become obvious that the assembly of the T3SS is not a unidirectional and deterministic process, but that parts of the T3SS constantly exchange or rearrange. This article aims to give an overview on the assembly and post-assembly dynamics of the T3SS, with a focus on emerging general concepts and adaptations of the general assembly pathway.
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Affiliation(s)
- Andreas Diepold
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Straße 10, 35043, Marburg, Germany.
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Molecular Organization and Assembly of the Export Apparatus of Flagellar Type III Secretion Systems. Curr Top Microbiol Immunol 2019; 427:91-107. [PMID: 31172377 DOI: 10.1007/82_2019_170] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The bacterial flagellum is a supramolecular motility machine consisting of the basal body, the hook, and the filament. For construction of the flagellum beyond the cellular membranes, a type III protein export apparatus uses ATP and proton-motive force (PMF) across the cytoplasmic membrane as the energy sources to transport flagellar component proteins from the cytoplasm to the distal end of the growing flagellar structure. The protein export apparatus consists of a PMF-driven transmembrane export gate complex and a cytoplasmic ATPase complex. In addition, the basal body C ring acts as a sorting platform for the cytoplasmic ATPase complex that efficiently brings export substrates and type III export chaperone-substrate complexes from the cytoplasm to the export gate complex. In this book chapter, we will summarize our current understanding of molecular organization and assembly of the flagellar type III protein export apparatus.
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Wagner S, Grin I, Malmsheimer S, Singh N, Torres-Vargas CE, Westerhausen S. Bacterial type III secretion systems: a complex device for the delivery of bacterial effector proteins into eukaryotic host cells. FEMS Microbiol Lett 2018; 365:5068689. [PMID: 30107569 PMCID: PMC6140923 DOI: 10.1093/femsle/fny201] [Citation(s) in RCA: 112] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 08/08/2018] [Indexed: 12/21/2022] Open
Abstract
Virulence-associated type III secretion systems (T3SS) serve the injection of bacterial effector proteins into eukaryotic host cells. They are able to secrete a great diversity of substrate proteins in order to modulate host cell function, and have evolved to sense host cell contact and to inject their substrates through a translocon pore in the host cell membrane. T3SS substrates contain an N-terminal signal sequence and often a chaperone-binding domain for cognate T3SS chaperones. These signals guide the substrates to the machine where substrates are unfolded and handed over to the secretion channel formed by the transmembrane domains of the export apparatus components and by the needle filament. Secretion itself is driven by the proton motive force across the bacterial inner membrane. The needle filament measures 20-150 nm in length and is crowned by a needle tip that mediates host-cell sensing. Secretion through T3SS is a highly regulated process with early, intermediate and late substrates. A strict secretion hierarchy is required to build an injectisome capable of reaching, sensing and penetrating the host cell membrane, before host cell-acting effector proteins are deployed. Here, we review the recent progress on elucidating the assembly, structure and function of T3SS injectisomes.
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Affiliation(s)
- Samuel Wagner
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
- German Center for Infection Research (DZIF), partner-site Tübingen, Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Iwan Grin
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Silke Malmsheimer
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Nidhi Singh
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Claudia E Torres-Vargas
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Sibel Westerhausen
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
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Tusk SE, Delalez NJ, Berry RM. Subunit Exchange in Protein Complexes. J Mol Biol 2018; 430:4557-4579. [DOI: 10.1016/j.jmb.2018.06.039] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Revised: 06/21/2018] [Accepted: 06/21/2018] [Indexed: 01/09/2023]
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Lam KH, Xue C, Sun K, Zhang H, Lam WWL, Zhu Z, Ng JTY, Sause WE, Lertsethtakarn P, Lau KF, Ottemann KM, Au SWN. Three SpoA-domain proteins interact in the creation of the flagellar type III secretion system in Helicobacter pylori. J Biol Chem 2018; 293:13961-13973. [PMID: 29991595 PMCID: PMC6130963 DOI: 10.1074/jbc.ra118.002263] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Revised: 06/07/2018] [Indexed: 01/07/2023] Open
Abstract
Bacterial flagella are rotary nanomachines that contribute to bacterial fitness in many settings, including host colonization. The flagellar motor relies on the multiprotein flagellar motor-switch complex to govern flagellum formation and rotational direction. Different bacteria exhibit great diversity in their flagellar motors. One such variation is exemplified by the motor-switch apparatus of the gastric pathogen Helicobacter pylori, which carries an extra switch protein, FliY, along with the more typical FliG, FliM, and FliN proteins. All switch proteins are needed for normal flagellation and motility in H. pylori, but the molecular mechanism of their assembly is unknown. To fill this gap, we examined the interactions among these proteins. We found that the C-terminal SpoA domain of FliY (FliYC) is critical to flagellation and forms heterodimeric complexes with the FliN and FliM SpoA domains, which are β-sheet domains of type III secretion system proteins. Surprisingly, unlike in other flagellar switch systems, neither FliY nor FliN self-associated. The crystal structure of the FliYC-FliNC complex revealed a saddle-shaped structure homologous to the FliN-FliN dimer of Thermotoga maritima, consistent with a FliY-FliN heterodimer forming the functional unit. Analysis of the FliYC-FliNC interface indicated that oppositely charged residues specific to each protein drive heterodimer formation. Moreover, both FliYC-FliMC and FliYC-FliNC associated with the flagellar regulatory protein FliH, explaining their important roles in flagellation. We conclude that H. pylori uses a FliY-FliN heterodimer instead of a homodimer and creates a switch complex with SpoA domains derived from three distinct proteins.
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Affiliation(s)
- Kwok Ho Lam
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong
| | - Chaolun Xue
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong, ,Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen 518057, China, and
| | - Kailei Sun
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong
| | - Huawei Zhang
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong, ,Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen 518057, China, and
| | - Wendy Wai Ling Lam
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong, ,Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen 518057, China, and
| | - Zeyu Zhu
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong
| | - Juliana Tsz Yan Ng
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong
| | - William E. Sause
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, California 95064
| | - Paphavee Lertsethtakarn
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, California 95064
| | - Kwok Fai Lau
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong
| | - Karen M. Ottemann
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, California 95064
| | - Shannon Wing Ngor Au
- From the Center for Protein Science and Crystallography, School of Life Sciences, Faculty of Science, Chinese University of Hong Kong, Shatin, Hong Kong, ,Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen 518057, China, and ,To whom correspondence should be addressed. Tel.:
852-3943-4170; E-mail:
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dos Santos RN, Khan S, Morcos F. Characterization of C-ring component assembly in flagellar motors from amino acid coevolution. ROYAL SOCIETY OPEN SCIENCE 2018; 5:171854. [PMID: 29892378 PMCID: PMC5990795 DOI: 10.1098/rsos.171854] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2017] [Accepted: 04/05/2018] [Indexed: 06/08/2023]
Abstract
Bacterial flagellar motility, an important virulence factor, is energized by a rotary motor localized within the flagellar basal body. The rotor module consists of a large framework (the C-ring), composed of the FliG, FliM and FliN proteins. FliN and FliM contacts the FliG torque ring to control the direction of flagellar rotation. We report that structure-based models constrained only by residue coevolution can recover the binding interface of atomic X-ray dimer complexes with remarkable accuracy (approx. 1 Å RMSD). We propose a model for FliM-FliN heterodimerization, which agrees accurately with homologous interfaces as well as in situ cross-linking experiments, and hence supports a proposed architecture for the lower portion of the C-ring. Furthermore, this approach allowed the identification of two discrete and interchangeable homodimerization interfaces between FliM middle domains that agree with experimental measurements and might be associated with C-ring directional switching dynamics triggered upon binding of CheY signal protein. Our findings provide structural details of complex formation at the C-ring that have been difficult to obtain with previous methodologies and clarify the architectural principle that underpins the ultra-sensitive allostery exhibited by this ring assembly that controls the clockwise or counterclockwise rotation of flagella.
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Affiliation(s)
- Ricardo Nascimento dos Santos
- Institute of Chemistry and Center for Computational Engineering and Science, University of Campinas, Campinas, SP, Brazil
| | - Shahid Khan
- Molecular Biology Consortium, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Faruck Morcos
- Department of Biological Sciences, University of Texas at Dallas, Richardson, TX, USA
- Department of Bioengineering, University of Texas at Dallas, Richardson, TX, USA
- Center for Systems Biology, University of Texas at Dallas, Richardson, TX, USA
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Rocha JM, Richardson CJ, Zhang M, Darch CM, Cai E, Diepold A, Gahlmann A. Single-molecule tracking in liveYersinia enterocoliticareveals distinct cytosolic complexes of injectisome subunits. Integr Biol (Camb) 2018; 10:502-515. [DOI: 10.1039/c8ib00075a] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Single-molecule tracking of bound (blue trajectories) and diffusive (red trajectories) injectisome subunits reveals the formation of distinct cytosolic complexes.
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Affiliation(s)
| | | | - Mingxing Zhang
- Department of Chemistry, University of Virginia
- Charlottesville
- USA
| | | | - Eugene Cai
- Department of Chemistry, University of Virginia
- Charlottesville
- USA
| | - Andreas Diepold
- Department of Ecophysiology
- Max Planck Institute for Terrestrial Microbiology
- Marburg
- Germany
| | - Andreas Gahlmann
- Department of Chemistry, University of Virginia
- Charlottesville
- USA
- Department of Molecular Physiology & Biological Physics, University of Virginia School of Medicine
- Charlottesville
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A dynamic and adaptive network of cytosolic interactions governs protein export by the T3SS injectisome. Nat Commun 2017; 8:15940. [PMID: 28653671 PMCID: PMC5490264 DOI: 10.1038/ncomms15940] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Accepted: 05/15/2017] [Indexed: 12/03/2022] Open
Abstract
Many bacteria use a type III secretion system (T3SS) to inject effector proteins into host cells. Selection and export of the effectors is controlled by a set of soluble proteins at the cytosolic interface of the membrane spanning type III secretion ‘injectisome’. Combining fluorescence microscopy, biochemical interaction studies and fluorescence correlation spectroscopy, we show that in live Yersinia enterocolitica bacteria these soluble proteins form complexes both at the injectisome and in the cytosol. Binding to the injectisome stabilizes these cytosolic complexes, whereas the free cytosolic complexes, which include the type III secretion ATPase, constitute a highly dynamic and adaptive network. The extracellular calcium concentration, which triggers activation of the T3SS, directly influences the cytosolic complexes, possibly through the essential component SctK/YscK, revealing a potential mechanism involved in the regulation of type III secretion. Bacterial type III secretion systems (T3SS) play important roles in pathogenesis. Here, Diepold et al. show the dynamic nature of complexes formed of essential T3SS components in live bacteria, and that extracellular calcium concentrations influence these cytosolic complexes likely via SctK/YscK.
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49
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Control of type III protein secretion using a minimal genetic system. Nat Commun 2017; 8:14737. [PMID: 28485369 PMCID: PMC5436071 DOI: 10.1038/ncomms14737] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 01/27/2017] [Indexed: 01/12/2023] Open
Abstract
Gram-negative bacteria secrete proteins using a type III secretion system (T3SS), which functions as a needle-like molecular machine. The many proteins involved in T3SS construction are tightly regulated due to its role in pathogenesis and motility. Here, starting with the 35 kb Salmonella pathogenicity island 1 (SPI-1), we eliminated internal regulation and simplified the genetics by removing or recoding genes, scrambling gene order and replacing all non-coding DNA with synthetic genetic parts. This process results in a 16 kb cluster that shares no sequence identity, regulation or organizational principles with SPI-1. Building this simplified system led to the discovery of essential roles for an internal start site (SpaO) and small RNA (InvR). Further, it can be controlled using synthetic regulatory circuits, including under SPI-1 repressing conditions. This work reveals an incredible post-transcriptional robustness in T3SS assembly and aids its control as a tool in biotechnology.
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Abstract
Type III secretion systems (T3SSs) are protein transport nanomachines that are found in Gram-negative bacterial pathogens and symbionts. Resembling molecular syringes, T3SSs form channels that cross the bacterial envelope and the host cell membrane, which enable bacteria to inject numerous effector proteins into the host cell cytoplasm and establish trans-kingdom interactions with diverse hosts. Recent advances in cryo-electron microscopy and integrative imaging have provided unprecedented views of the architecture and structure of T3SSs. Furthermore, genetic and molecular analyses have elucidated the functions of many effectors and key regulators of T3SS assembly and secretion hierarchy, which is the sequential order by which the protein substrates are secreted. As essential virulence factors, T3SSs are attractive targets for vaccines and therapeutics. This Review summarizes our current knowledge of the structure and function of this important protein secretion machinery. A greater understanding of T3SSs should aid mechanism-based drug design and facilitate their manipulation for biotechnological applications.
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