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Worrall LJ, Majewski DD, Strynadka NCJ. Structural Insights into Type III Secretion Systems of the Bacterial Flagellum and Injectisome. Annu Rev Microbiol 2023; 77:669-698. [PMID: 37713458 DOI: 10.1146/annurev-micro-032521-025503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/17/2023]
Abstract
Two of the most fascinating bacterial nanomachines-the broadly disseminated rotary flagellum at the heart of cellular motility and the eukaryotic cell-puncturing injectisome essential to specific pathogenic species-utilize at their core a conserved export machinery called the type III secretion system (T3SS). The T3SS not only secretes the components that self-assemble into their extracellular appendages but also, in the case of the injectisome, subsequently directly translocates modulating effector proteins from the bacterial cell into the infected host. The injectisome is thought to have evolved from the flagellum as a minimal secretory system lacking motility, with the subsequent acquisition of additional components tailored to its specialized role in manipulating eukaryotic hosts for pathogenic advantage. Both nanomachines have long been the focus of intense interest, but advances in structural and functional understanding have taken a significant step forward since 2015, facilitated by the revolutionary advances in cryo-electron microscopy technologies. With several seminal structures of each nanomachine now captured, we review here the molecular similarities and differences that underlie their diverse functions.
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Affiliation(s)
- Liam J Worrall
- Department of Biochemistry and Molecular Biology and Centre for Blood Research, The University of British Columbia, Vancouver, British Columbia, Canada; , ,
| | - Dorothy D Majewski
- Department of Biochemistry and Molecular Biology and Centre for Blood Research, The University of British Columbia, Vancouver, British Columbia, Canada; , ,
- Current affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts, USA
| | - Natalie C J Strynadka
- Department of Biochemistry and Molecular Biology and Centre for Blood Research, The University of British Columbia, Vancouver, British Columbia, Canada; , ,
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2
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Minamino T, Kinoshita M, Morimoto YV, Namba K. Activation mechanism of the bacterial flagellar dual-fuel protein export engine. Biophys Physicobiol 2022; 19:e190046. [PMID: 36567733 PMCID: PMC9751260 DOI: 10.2142/biophysico.bppb-v19.0046] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Accepted: 11/17/2022] [Indexed: 11/19/2022] Open
Abstract
Bacteria employ the flagellar type III secretion system (fT3SS) to construct flagellum, which acts as a supramolecular motility machine. The fT3SS of Salmonella enterica serovar Typhimurium is composed of a transmembrane export gate complex and a cytoplasmic ATPase ring complex. The transmembrane export gate complex is fueled by proton motive force across the cytoplasmic membrane and is divided into four distinct functional parts: a dual-fuel export engine; a polypeptide channel; a membrane voltage sensor; and a docking platform. ATP hydrolysis by the cytoplasmic ATPase complex converts the export gate complex into a highly efficient proton (H+)/protein antiporter that couples inward-directed H+ flow with outward-directed protein export. When the ATPase ring complex does not work well in a given environment, the export gate complex will remain inactive. However, when the electric potential difference, which is defined as membrane voltage, rises above a certain threshold value, the export gate complex becomes an active H+/protein antiporter to a considerable degree, suggesting that the export gate complex has a voltage-gated activation mechanism. Furthermore, the export gate complex also has a sodium ion (Na+) channel to couple Na+ influx with flagellar protein export. In this article, we review our current understanding of the activation mechanism of the dual-fuel protein export engine of the fT3SS. This review article is an extended version of a Japanese article, Membrane voltage-dependent activation of the transmembrane export gate complex in the bacterial flagellar type III secretion system, published in SEIBUTSU BUTSURI Vol. 62, p165-169 (2022).
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Affiliation(s)
- Tohru Minamino
- Graduate school of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
| | - Miki Kinoshita
- Graduate school of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
| | - Yusuke V. Morimoto
- Department of Physics and Information Technology, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Iizuka, Fukuoka 820-8502, Japan,Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
| | - Keiichi Namba
- Graduate school of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan,RIKEN SPring-8 Center, Suita, Osaka 565-0871, Japan,JEOL YOKOGUSHI Research Alliance Laboratories, Osaka University, Suita, Osaka 565-0871, Japan
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3
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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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4
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Omnus DJ, Fink MJ, Szwedo K, Jonas K. The Lon protease temporally restricts polar cell differentiation events during the Caulobacter cell cycle. eLife 2021; 10:73875. [PMID: 34693909 PMCID: PMC8545394 DOI: 10.7554/elife.73875] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 09/22/2021] [Indexed: 01/16/2023] Open
Abstract
The highly conserved protease Lon has important regulatory and protein quality control functions in cells from the three domains of life. Despite many years of research on Lon, only a few specific protein substrates are known in most organisms. Here, we used a quantitative proteomics approach to identify novel substrates of Lon in the dimorphic bacterium Caulobacter crescentus. We focused our study on proteins involved in polar cell differentiation and investigated the developmental regulator StaR and the flagella hook length regulator FliK as specific Lon substrates in detail. We show that Lon recognizes these proteins at their C-termini, and that Lon-dependent degradation ensures their temporally restricted accumulation in the cell cycle phase when their function is needed. Disruption of this precise temporal regulation of StaR and FliK levels in a Δlon mutant contributes to defects in stalk biogenesis and motility, respectively, revealing a critical role of Lon in coordinating developmental processes with cell cycle progression. Our work underscores the importance of Lon in the regulation of complex temporally controlled processes by adjusting the concentrations of critical regulatory proteins. Furthermore, this study includes the first characterization of FliK in C. crescentus and uncovers a dual role of the C-terminal amino acids of FliK in protein function and degradation.
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Affiliation(s)
- Deike J Omnus
- Science for Life Laboratory and Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Matthias J Fink
- Science for Life Laboratory and Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Klaudia Szwedo
- Science for Life Laboratory and Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Kristina Jonas
- Science for Life Laboratory and Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
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5
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The polar flagellar transcriptional regulatory network in Vibrio campbellii deviates from canonical Vibrio species. J Bacteriol 2021; 203:e0027621. [PMID: 34339299 DOI: 10.1128/jb.00276-21] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Swimming motility is a critical virulence factor in pathogenesis for numerous Vibrio species. Vibrio campbellii DS40M4 is a wild isolate that has been recently established as a highly tractable model strain for bacterial genetics studies. We sought to exploit the tractability and relevance of this strain for characterization of flagellar gene regulation in V. campbellii. Using comparative genomics, we identified homologs of V. campbellii flagellar and chemotaxis genes conserved in other members of the Vibrionaceae and determined the transcriptional profile of these loci using differential RNA-seq. We systematically deleted all 63 predicted flagellar and chemotaxis genes in V. campbellii and examined their effects on motility and flagellum production. We specifically focused on the core regulators of the flagellar hierarchy established in other vibrios: RpoN (σ54), FlrA, FlrC, and FliA. Our results show that V. campbellii transcription of flagellar and chemotaxis genes is governed by a multi-tiered regulatory hierarchy similar to other motile Vibrio species. However, there are several critical differences in V. campbellii: (i) the σ54-dependent regulator FlrA is dispensable for motility, (ii) the flgA, fliEFGHIJ, flrA, and flrBC operons do not require σ54 for expression, and (iii) FlrA and FlrC co-regulate class II genes. Our model proposes that the V. campbellii flagellar transcriptional hierarchy has three classes of genes, in contrast to the four-class hierarchy in Vibrio cholerae. Our genetic and phenotypic dissection of the V. campbellii flagellar regulatory network highlights the differences that have evolved in flagellar regulation across the Vibrionaceae. Importance Vibrio campbellii is a Gram-negative bacterium that is free-living and ubiquitous in marine environments and is an important global pathogen of fish and shellfish. Disruption of the flagellar motor significantly decreases host mortality of V. campbellii, suggesting that motility is a key factor in pathogenesis. Using this model organism, we identified >60 genes that encode proteins with predicted structural, mechanical, or regulatory roles in function of the single polar flagellum in V. campbellii. We systematically tested strains containing single deletions of each gene to determine the impact on motility and flagellum production. Our studies have uncovered differences in the regulatory network and function of several genes in V. campbellii as compared to established systems in Vibrio cholerae and Vibrio parahaemolyticus.
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6
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Bacterial Flagellar Filament: A Supramolecular Multifunctional Nanostructure. Int J Mol Sci 2021; 22:ijms22147521. [PMID: 34299141 PMCID: PMC8306008 DOI: 10.3390/ijms22147521] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Revised: 07/06/2021] [Accepted: 07/10/2021] [Indexed: 02/07/2023] Open
Abstract
The bacterial flagellum is a complex and dynamic nanomachine that propels bacteria through liquids. It consists of a basal body, a hook, and a long filament. The flagellar filament is composed of thousands of copies of the protein flagellin (FliC) arranged helically and ending with a filament cap composed of an oligomer of the protein FliD. The overall structure of the filament core is preserved across bacterial species, while the outer domains exhibit high variability, and in some cases are even completely absent. Flagellar assembly is a complex and energetically costly process triggered by environmental stimuli and, accordingly, highly regulated on transcriptional, translational and post-translational levels. Apart from its role in locomotion, the filament is critically important in several other aspects of bacterial survival, reproduction and pathogenicity, such as adhesion to surfaces, secretion of virulence factors and formation of biofilms. Additionally, due to its ability to provoke potent immune responses, flagellins have a role as adjuvants in vaccine development. In this review, we summarize the latest knowledge on the structure of flagellins, capping proteins and filaments, as well as their regulation and role during the colonization and infection of the host.
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Nariya MK, Mallela A, Shi JJ, Deeds EJ. Robustness and the evolution of length control strategies in the T3SS and flagellar hook. Biophys J 2021; 120:3820-3830. [PMID: 34246629 DOI: 10.1016/j.bpj.2021.05.032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 04/22/2021] [Accepted: 05/20/2021] [Indexed: 11/16/2022] Open
Abstract
Bacterial cells construct many structures, such as the flagellar hook and the type III secretion system (T3SS) injectisome, that aid in crucial physiological processes such as locomotion and pathogenesis. Both of these structures involve long extracellular channels, and the length of these channels must be highly regulated in order for these structures to perform their intended functions. There are two leading models for how length control is achieved in the flagellar hook and T3SS needle: the substrate switching model, in which the length is controlled by assembly of an inner rod, and the ruler model, in which a molecular ruler controls the length. Although there is qualitative experimental evidence to support both models, comparatively little has been done to quantitatively characterize these mechanisms or make detailed predictions that could be used to unambiguously test these mechanisms experimentally. In this work, we constructed a mathematical model of length control based on the ruler mechanism and found that the predictions of this model are consistent with experimental data-not just for the scaling of the average length with the ruler protein length, but also for the variance. Interestingly, we found that the ruler mechanism allows for the evolution of needles with large average lengths without the concomitant large increase in variance that occurs in the substrate switching mechanism. In addition to making further predictions that can be tested experimentally, these findings shed new light on the trade-offs that may have led to the evolution of different length control mechanisms in different bacterial species.
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Affiliation(s)
- Maulik K Nariya
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas
| | - Abhishek Mallela
- Department of Biostatistics, University of Kansas Medical Center, Kansas City, Kansas
| | - Jack J Shi
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas
| | - Eric J Deeds
- Center for Computational Biology, University of Kansas, Lawrence, Kansas; Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas.
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8
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Singh MK, Zangoui P, Yamanaka Y, Kenney LJ. Genetic code expansion enables visualization of Salmonella type three secretion system components and secreted effectors. eLife 2021; 10:67789. [PMID: 34061032 PMCID: PMC8192122 DOI: 10.7554/elife.67789] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 05/22/2021] [Indexed: 12/14/2022] Open
Abstract
Type three secretion systems enable bacterial pathogens to inject effectors into the cytosol of eukaryotic hosts to reprogram cellular functions. It is technically challenging to label effectors and the secretion machinery without disrupting their structure/function. Herein, we present a new approach for labeling and visualization of previously intractable targets. Using genetic code expansion, we site-specifically labeled SsaP, the substrate specificity switch, and SifA, a here-to-fore unlabeled secreted effector. SsaP was secreted at later infection times; SsaP labeling demonstrated the stochasticity of injectisome and effector expression. SifA was labeled after secretion into host cells via fluorescent unnatural amino acids or non-fluorescent labels and a subsequent click reaction. We demonstrate the superiority of imaging after genetic code expansion compared to small molecule tags. It provides an alternative for labeling proteins that do not tolerate N- or C-terminal tags or fluorophores and thus is widely applicable to other secreted effectors and small proteins.
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Affiliation(s)
- Moirangthem Kiran Singh
- Mechanobiology Institute, T-Lab, 5A Engineering Drive 1, National University of Singapore, Singapore, Singapore.,Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, United States
| | - Parisa Zangoui
- Mechanobiology Institute, T-Lab, 5A Engineering Drive 1, National University of Singapore, Singapore, Singapore.,Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, United States
| | - Yuki Yamanaka
- Mechanobiology Institute, T-Lab, 5A Engineering Drive 1, National University of Singapore, Singapore, Singapore
| | - Linda J Kenney
- Mechanobiology Institute, T-Lab, 5A Engineering Drive 1, National University of Singapore, Singapore, Singapore.,Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, United States
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9
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Inoue Y, Kinoshita M, Kida M, Takekawa N, Namba K, Imada K, Minamino T. The FlhA linker mediates flagellar protein export switching during flagellar assembly. Commun Biol 2021; 4:646. [PMID: 34059784 PMCID: PMC8166844 DOI: 10.1038/s42003-021-02177-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Accepted: 05/04/2021] [Indexed: 12/15/2022] Open
Abstract
The flagellar protein export apparatus switches substrate specificity from hook-type to filament-type upon hook assembly completion, thereby initiating filament assembly at the hook tip. The C-terminal cytoplasmic domain of FlhA (FlhAC) serves as a docking platform for flagellar chaperones in complex with their cognate filament-type substrates. Interactions of the flexible linker of FlhA (FlhAL) with its nearest FlhAC subunit in the FlhAC ring is required for the substrate specificity switching. To address how FlhAL brings the order to flagellar assembly, we analyzed the flhA(E351A/W354A/D356A) ΔflgM mutant and found that this triple mutation in FlhAL increased the secretion level of hook protein by 5-fold, thereby increasing hook length. The crystal structure of FlhAC(E351A/D356A) showed that FlhAL bound to the chaperone-binding site of its neighboring subunit. We propose that the interaction of FlhAL with the chaperon-binding site of FlhAC suppresses filament-type protein export and facilitates hook-type protein export during hook assembly.
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Affiliation(s)
- Yumi Inoue
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.,Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Miki Kinoshita
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Mamoru Kida
- Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
| | - Norihiro Takekawa
- Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.,RIKEN SPring-8 Center and Center for Biosystems Dynamics Research, Suita, Osaka, Japan.,JEOL YOKOGUSHI Research Alliance Laboratories, Osaka University, Suita, Osaka, Japan
| | - Katsumi Imada
- Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan.
| | - Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.
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10
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Miletic S, Fahrenkamp D, Goessweiner-Mohr N, Wald J, Pantel M, Vesper O, Kotov V, Marlovits TC. Substrate-engaged type III secretion system structures reveal gating mechanism for unfolded protein translocation. Nat Commun 2021; 12:1546. [PMID: 33750771 PMCID: PMC7943601 DOI: 10.1038/s41467-021-21143-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 01/06/2021] [Indexed: 02/06/2023] Open
Abstract
Many bacterial pathogens rely on virulent type III secretion systems (T3SSs) or injectisomes to translocate effector proteins in order to establish infection. The central component of the injectisome is the needle complex which assembles a continuous conduit crossing the bacterial envelope and the host cell membrane to mediate effector protein translocation. However, the molecular principles underlying type III secretion remain elusive. Here, we report a structure of an active Salmonella enterica serovar Typhimurium needle complex engaged with the effector protein SptP in two functional states, revealing the complete 800Å-long secretion conduit and unraveling the critical role of the export apparatus (EA) subcomplex in type III secretion. Unfolded substrates enter the EA through a hydrophilic constriction formed by SpaQ proteins, which enables side chain-independent substrate transport. Above, a methionine gasket formed by SpaP proteins functions as a gate that dilates to accommodate substrates while preventing leaky pore formation. Following gate penetration, a moveable SpaR loop first folds up to then support substrate transport. Together, these findings establish the molecular basis for substrate translocation through T3SSs and improve our understanding of bacterial pathogenicity and motility.
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Affiliation(s)
- Sean Miletic
- University Medical Center Hamburg-Eppendorf (UKE), Institute of Structural and Systems Biology, Hamburg, Germany.,Centre for Structural Systems Biology (CSSB), Hamburg, Germany.,Deutsches Elektronen-Synchrotron Zentrum (DESY), Hamburg, Germany.,Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria.,Research Institute of Molecular Pathology (IMP), Vienna, Austria
| | - Dirk Fahrenkamp
- University Medical Center Hamburg-Eppendorf (UKE), Institute of Structural and Systems Biology, Hamburg, Germany.,Centre for Structural Systems Biology (CSSB), Hamburg, Germany.,Deutsches Elektronen-Synchrotron Zentrum (DESY), Hamburg, Germany
| | - Nikolaus Goessweiner-Mohr
- University Medical Center Hamburg-Eppendorf (UKE), Institute of Structural and Systems Biology, Hamburg, Germany.,Deutsches Elektronen-Synchrotron Zentrum (DESY), Hamburg, Germany.,Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria.,Research Institute of Molecular Pathology (IMP), Vienna, Austria
| | - Jiri Wald
- University Medical Center Hamburg-Eppendorf (UKE), Institute of Structural and Systems Biology, Hamburg, Germany.,Centre for Structural Systems Biology (CSSB), Hamburg, Germany.,Deutsches Elektronen-Synchrotron Zentrum (DESY), Hamburg, Germany.,Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria.,Research Institute of Molecular Pathology (IMP), Vienna, Austria
| | - Maurice Pantel
- University Medical Center Hamburg-Eppendorf (UKE), Institute of Structural and Systems Biology, Hamburg, Germany.,Centre for Structural Systems Biology (CSSB), Hamburg, Germany.,Deutsches Elektronen-Synchrotron Zentrum (DESY), Hamburg, Germany
| | - Oliver Vesper
- University Medical Center Hamburg-Eppendorf (UKE), Institute of Structural and Systems Biology, Hamburg, Germany.,Centre for Structural Systems Biology (CSSB), Hamburg, Germany.,Deutsches Elektronen-Synchrotron Zentrum (DESY), Hamburg, Germany.,Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria.,Research Institute of Molecular Pathology (IMP), Vienna, Austria
| | - Vadim Kotov
- University Medical Center Hamburg-Eppendorf (UKE), Institute of Structural and Systems Biology, Hamburg, Germany.,Centre for Structural Systems Biology (CSSB), Hamburg, Germany.,Deutsches Elektronen-Synchrotron Zentrum (DESY), Hamburg, Germany.,Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria.,Research Institute of Molecular Pathology (IMP), Vienna, Austria
| | - Thomas C Marlovits
- University Medical Center Hamburg-Eppendorf (UKE), Institute of Structural and Systems Biology, Hamburg, Germany. .,Centre for Structural Systems Biology (CSSB), Hamburg, Germany. .,Deutsches Elektronen-Synchrotron Zentrum (DESY), Hamburg, Germany. .,Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria. .,Research Institute of Molecular Pathology (IMP), Vienna, Austria.
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11
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Protein Export via the Type III Secretion System of the Bacterial Flagellum. Biomolecules 2021; 11:biom11020186. [PMID: 33572887 PMCID: PMC7911332 DOI: 10.3390/biom11020186] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Revised: 01/25/2021] [Accepted: 01/26/2021] [Indexed: 12/15/2022] Open
Abstract
The bacterial flagellum and the related virulence-associated injectisome system of pathogenic bacteria utilize a type III secretion system (T3SS) to export substrate proteins across the inner membrane in a proton motive force-dependent manner. The T3SS is composed of an export gate (FliPQR/FlhA/FlhB) located in the flagellar basal body and an associated soluble ATPase complex in the cytoplasm (FliHIJ). Here, we summarise recent insights into the structure, assembly and protein secretion mechanisms of the T3SS with a focus on energy transduction and protein transport across the cytoplasmic membrane.
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12
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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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13
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Attieh Z, Mouawad C, Rejasse A, Jehanno I, Perchat S, Hegna IK, Økstad OA, Kallassy Awad M, Sanchis-Borja V, El Chamy L. The fliK Gene Is Required for the Resistance of Bacillus thuringiensis to Antimicrobial Peptides and Virulence in Drosophila melanogaster. Front Microbiol 2020; 11:611220. [PMID: 33391240 PMCID: PMC7775485 DOI: 10.3389/fmicb.2020.611220] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 11/18/2020] [Indexed: 11/13/2022] Open
Abstract
Antimicrobial peptides (AMPs) are essential effectors of the host innate immune system and they represent promising molecules for the treatment of multidrug resistant microbes. A better understanding of microbial resistance to these defense peptides is thus prerequisite for the control of infectious diseases. Here, using a random mutagenesis approach, we identify the fliK gene, encoding an internal molecular ruler that controls flagella hook length, as an essential element for Bacillus thuringiensis resistance to AMPs in Drosophila. Unlike its parental strain, that is highly virulent to both wild-type and AMPs deficient mutant flies, the fliK deletion mutant is only lethal to the latter's. In agreement with its conserved function, the fliK mutant is non-flagellated and exhibits highly compromised motility. However, comparative analysis of the fliK mutant phenotype to that of a fla mutant, in which the genes encoding flagella proteins are interrupted, indicate that B. thuringiensis FliK-dependent resistance to AMPs is independent of flagella assembly. As a whole, our results identify FliK as an essential determinant for B. thuringiensis virulence in Drosophila and provide new insights on the mechanisms underlying bacteria resistance to AMPs.
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Affiliation(s)
- Zaynoun Attieh
- UR-EGP, Faculté des Sciences, Université Saint-Joseph de Beyrouth, Beirut, Lebanon
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France
| | - Carine Mouawad
- UR-EGP, Faculté des Sciences, Université Saint-Joseph de Beyrouth, Beirut, Lebanon
| | - Agnès Rejasse
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France
| | - Isabelle Jehanno
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France
| | - Stéphane Perchat
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France
| | - Ida K. Hegna
- Department of Pharmacy, Centre for Integrative Microbial Evolution (CIME), Faculty of Mathematics and Natural Sciences, University of Oslo, Oslo, Norway
| | - Ole A. Økstad
- Department of Pharmacy, Centre for Integrative Microbial Evolution (CIME), Faculty of Mathematics and Natural Sciences, University of Oslo, Oslo, Norway
| | | | - Vincent Sanchis-Borja
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France
| | - Laure El Chamy
- UR-EGP, Faculté des Sciences, Université Saint-Joseph de Beyrouth, Beirut, Lebanon
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14
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Zhang K, He J, Cantalano C, Guo Y, Liu J, Li C. FlhF regulates the number and configuration of periplasmic flagella in Borrelia burgdorferi. Mol Microbiol 2020; 113:1122-1139. [PMID: 32039533 DOI: 10.1111/mmi.14482] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 02/03/2020] [Accepted: 02/04/2020] [Indexed: 12/17/2022]
Abstract
The Lyme disease bacterium Borrelia burgdorferi has 7-11 periplasmic flagella (PF) that arise from the cell poles and extend toward the midcell as a flat-ribbon, which is distinct from other bacteria. FlhF, a signal recognition particle (SRP)-like GTPase, has been found to regulate the flagellar number and polarity; however, its role in B. burgdorferi remains unknown. B. burgdorferi has an FlhF homolog (BB0270). Structural and biochemical analyses show that BB0270 has a similar structure and enzymatic activity as its counterparts from other bacteria. Genetics and cryo-electron tomography studies reveal that deletion of BB0270 leads to mutant cells that have less PF (4 ± 2 PF per cell tip) and fail to form a flat-ribbon, indicative of a role of BB0270 in the control of PF number and configuration. Mechanistically, we demonstrate that BB0270 localizes at the cell poles and controls the number and position of PF via regulating the flagellar protein stability and the polar localization of the MS-ring protein FliF. Our study not only provides the detailed characterizations of BB0270 and its profound impacts on flagellar assembly, morphology and motility in B. burgdorferi, but also unveils mechanistic insights into how spirochetes control their unique flagellar patterns.
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Affiliation(s)
- Kai Zhang
- Philips Institute for Oral Health Research, School of Dentistry, Virginia Commonwealth University, Richmond, VA, USA
| | - Jun He
- Department of Microbial Pathogenesis, Microbial Sciences Institute, Yale University School of Medicine, New Haven, CT, USA
| | - Claudio Cantalano
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, USA.,Institute for Structural Biology, Drug Discovery and Development, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, USA
| | - Youzhong Guo
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, USA.,Institute for Structural Biology, Drug Discovery and Development, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, USA
| | - Jun Liu
- Department of Microbial Pathogenesis, Microbial Sciences Institute, Yale University School of Medicine, New Haven, CT, USA
| | - Chunhao Li
- Philips Institute for Oral Health Research, School of Dentistry, Virginia Commonwealth University, Richmond, VA, USA.,Department of Microbiology and Immunology, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
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15
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The flexible linker of the secreted FliK ruler is required for export switching of the flagellar protein export apparatus. Sci Rep 2020; 10:838. [PMID: 31964971 PMCID: PMC6972891 DOI: 10.1038/s41598-020-57782-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 01/02/2020] [Indexed: 12/19/2022] Open
Abstract
The hook length of the flagellum is controlled to about 55 nm in Salmonella. The flagellar type III protein export apparatus secretes FliK to determine hook length during hook assembly and changes its substrate specificity from the hook protein to the filament protein when the hook length has reached about 55 nm. Salmonella FliK consists of an N-terminal domain (FliKN, residues 1–207), a C-terminal domain (FliKC, residues 268–405) and a flexible linker (FliKL, residues 208–267) connecting these two domains. FliKN is a ruler to measure hook length. FliKC binds to a transmembrane export gate protein FlhB to undergo the export switching. FliKL not only acts as part of the ruler but also contributes to this switching event, but it remains unknown how. Here we report that FliKL is required for efficient interaction of FliKC with FlhB. Deletions in FliKL not only shortened hook length according to the size of deletions but also caused a loose length control. Deletion of residues 206–265 significantly reduced the binding affinity of FliKC for FlhB, thereby producing much longer hooks. We propose that an appropriate length of FliKL is required for efficient interaction of FliKC with FlhB.
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16
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FliK-Driven Conformational Rearrangements of FlhA and FlhB Are Required for Export Switching of the Flagellar Protein Export Apparatus. J Bacteriol 2020; 202:JB.00637-19. [PMID: 31712281 DOI: 10.1128/jb.00637-19] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 11/06/2019] [Indexed: 12/31/2022] Open
Abstract
FlhA and FlhB are transmembrane proteins of the flagellar type III protein export apparatus, and their C-terminal cytoplasmic domains (FlhAC and FlhBC) coordinate flagellar protein export with assembly. FlhBC undergoes autocleavage between Asn-269 and Pro-270 in a well-conserved NPTH loop located between FlhBCN and FlhBCC polypeptides and interacts with the C-terminal domain of the FliK ruler when the length of the hook has reached about 55 nm in Salmonella As a result, the flagellar protein export apparatus switches its substrate specificity, thereby terminating hook assembly and initiating filament assembly. The mechanism of export switching remains unclear. Here, we report the role of FlhBC cleavage in the switching mechanism. Photo-cross-linking experiments revealed that the flhB(N269A) and flhB(P270A) mutations did not affect the binding affinity of FlhBC for FliK. Genetic analysis of the flhB(P270A) mutant revealed that the P270A mutation affects a FliK-dependent conformational change of FlhBC, thereby inhibiting the substrate specificity switching. The flhA(A489E) mutation in FlhAC suppressed the flhB(P270A) mutation, suggesting that an interaction between FlhBC and FlhAC is critical for the export switching. We propose that the interaction between FliKC and a cleaved form of FlhBC promotes a conformational change in FlhBC responsible for the termination of hook-type protein export and a structural remodeling of the FlhAC ring responsible for the initiation of filament-type protein export.IMPORTANCE The flagellar type III protein export apparatus coordinates protein export with assembly, which allows the flagellum to be efficiently built at the cell surface. Hook completion is an important morphological checkpoint for the sequential flagellar assembly process. The protein export apparatus switches its substrate specificity from the hook protein to the filament protein upon hook completion. FliK, FlhB, and FlhA are involved in the export-switching process, but the mechanism remains a mystery. By analyzing a slow-cleaving flhB(P270A) mutant, we provide evidence that an interaction between FliK and FlhB induces conformational rearrangements in FlhB, followed by a structural remodeling of the FlhA ring structure that terminates hook assembly and initiates filament formation.
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17
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In Vitro Autonomous Construction of the Flagellar Axial Structure in Inverted Membrane Vesicles. Biomolecules 2020; 10:biom10010126. [PMID: 31940802 PMCID: PMC7022808 DOI: 10.3390/biom10010126] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 01/08/2020] [Accepted: 01/09/2020] [Indexed: 02/07/2023] Open
Abstract
The bacterial flagellum is a filamentous organelle extending from the cell surface. The axial structure of the flagellum consists of the rod, hook, junction, filament, and cap. The axial structure is formed by axial component proteins exported via a specific protein export apparatus in a well-regulated manner. Although previous studies have revealed the outline of the flagellar construction process, the mechanism of axial structure formation, including axial protein export, is still obscure due to difficulties in direct observation of protein export and assembly in vivo. We recently developed an in vitro flagellar protein transport assay system using inverted membrane vesicles (IMVs) and succeeded in reproducing the early stage of flagellar assembly. However, the late stage of the flagellar formation process remained to be examined in the IMVs. In this study, we showed that the filament-type proteins are transported into the IMVs to produce the filament on the hook inside the IMVs. Furthermore, we provide direct evidence that coordinated flagellar protein export and assembly can occur at the post-translational level. These results indicate that the ordered construction of the entire flagellar structure can be regulated by only the interactions between the protein export apparatus, the export substrate proteins, and their cognate chaperones.
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18
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Nakamura S, Hanaizumi Y, Morimoto YV, Inoue Y, Erhardt M, Minamino T, Namba K. Direct observation of speed fluctuations of flagellar motor rotation at extremely low load close to zero. Mol Microbiol 2019; 113:755-765. [DOI: 10.1111/mmi.14440] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 12/10/2019] [Accepted: 12/10/2019] [Indexed: 12/22/2022]
Affiliation(s)
- Shuichi Nakamura
- Department of Applied Physics, Graduate School of Engineering Tohoku University Sendai Japan
| | - Yuta Hanaizumi
- Department of Applied Physics, Graduate School of Engineering Tohoku University Sendai Japan
| | - Yusuke V. Morimoto
- Faculty of Computer Science and Systems Engineering, Department of Physics and Information Technology Kyushu Institute of Technology Fukuoka Japan
| | - Yumi Inoue
- Graduate School of Frontier Biosciences Osaka University Osaka Japan
| | - Marc Erhardt
- Institut für Biologie/Bakterienphysiologie Humboldt‐Universität zu Berlin Berlin Germany
| | - Tohru Minamino
- Graduate School of Frontier Biosciences Osaka University Osaka Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences Osaka University Osaka Japan
- RIKEN Spring‐8 Center and Center for Biosystems Dynamics Research Osaka Japan
- JEOL YOKOGUSHI Research Alliance Laboratories Osaka University Osaka Japan
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19
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Hooked on motility. Nat Struct Mol Biol 2019; 26:848-849. [PMID: 31570876 DOI: 10.1038/s41594-019-0302-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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20
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Lynch MJ, Miller M, James M, Zhang S, Zhang K, Li C, Charon NW, Crane BR. Structure and chemistry of lysinoalanine crosslinking in the spirochaete flagella hook. Nat Chem Biol 2019; 15:959-965. [PMID: 31406373 PMCID: PMC6764852 DOI: 10.1038/s41589-019-0341-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2019] [Accepted: 07/08/2019] [Indexed: 11/09/2022]
Abstract
The flagellar hook protein FlgE from spirochaete bacteria self-catalyzes the formation of an unusual inter-subunit lysinoalanine (Lal) crosslink that is critical for cell motility. Unlike other known examples of Lal biosynthesis, conserved cysteine and lysine residues in FlgE spontaneously react to form Lal without the involvement of additional enzymes. Oligomerization of FlgE via its D0 and Dc domains drives assembly of the crosslinking site at the D1-D2 domain interface. Structures of the FlgED2 domain, dehydroalanine (DHA) intermediate and Lal crosslinked FlgE subunits reveal successive snapshots of the reaction. Cys178 flips from a buried configuration to release hydrogen sulfide (H2S/HS-) and produce DHA. Interface residues provide hydrogen bonds to anchor the active site, facilitate β-elimination of Cys178 and polarize the peptide backbone to activate DHA for reaction with Lys165. Cysteine-reactive molecules accelerate DHA formation, whereas nucleophiles can intercept the DHA intermediate, thereby indicating a potential for Lal crosslink inhibitors to combat spirochaetal diseases.
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Affiliation(s)
- Michael J Lynch
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
| | - Michael Miller
- Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV, USA
| | - Milinda James
- Department of Microbiology, Immunology, and Cell Biology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV, USA
| | - Sheng Zhang
- Proteomics Facility, Institute of Biotechnology, Cornell University, Ithaca, NY, USA
| | - Kai Zhang
- Philips Institute for Oral Health Research, Virginia Commonwealth University School of Dentistry, Richmond, VA, USA
| | - Chunhao Li
- Philips Institute for Oral Health Research, Virginia Commonwealth University School of Dentistry, Richmond, VA, USA
| | - Nyles W Charon
- Department of Microbiology, Immunology, and Cell Biology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV, USA
| | - Brian R Crane
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA.
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21
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Inoue Y, Kinoshita M, Namba K, Minamino T. Mutational analysis of the C-terminal cytoplasmic domain of FlhB, a transmembrane component of the flagellar type III protein export apparatus in Salmonella. Genes Cells 2019; 24:408-421. [PMID: 30963674 DOI: 10.1111/gtc.12684] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Revised: 04/01/2019] [Accepted: 04/02/2019] [Indexed: 11/27/2022]
Abstract
The flagellar protein export apparatus switches its substrate specificity when hook length has reached approximately 55 nm in Salmonella. The C-terminal cytoplasmic domain of FlhB (FlhBC ) is involved in this switching process. FlhBC consists of FlhBCN and FlhBCC polypeptides. FlhBCC has a flexible C-terminal tail (FlhBCCT ). FlhBCC is involved in substrate recognition, and conformational rearrangements of FlhBCN -FlhBCC boundary are postulated to be required for the export switching. However, it remains unknown how it occurs. To clarify this question, we carried out mutational analysis of highly conserved residues in FlhBC . The flhB(E230A) mutation reduced the FlhB function. The flhB(E11S) mutation restored the protein transport activity of the flhB(E230A) mutant to the wild-type level, suggesting that the interaction of FlhBCN with the extreme N-terminal region of FlhB is required for flagellar protein export. The flhB(R320A) mutation affected hydrophobic interaction networks in FlhBCC , thereby increasing insolubility of FlhBC . The R320A mutation also affected the export switching, thereby producing longer hooks with the filament attached. C-terminal truncations of FlhBCCT induced a conformational change of FlhBCN -FlhBCC boundary, resulting in a loose hook length control. We propose that FlhBCCT may control conformational arrangements of FlhBCN -FlhBCC boundary through the hydrophobic interaction networks of FlhBCC .
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Affiliation(s)
- Yumi Inoue
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Miki Kinoshita
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.,RIKEN Center for Biosystems Dynamic Research & Spring-8 Center, Suita, Osaka, Japan
| | - Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
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22
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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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23
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Spöring I, Martinez VA, Hotz C, Schwarz-Linek J, Grady KL, Nava-Sedeño JM, Vissers T, Singer HM, Rohde M, Bourquin C, Hatzikirou H, Poon WCK, Dufour YS, Erhardt M. Hook length of the bacterial flagellum is optimized for maximal stability of the flagellar bundle. PLoS Biol 2018; 16:e2006989. [PMID: 30188886 PMCID: PMC6126814 DOI: 10.1371/journal.pbio.2006989] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 08/08/2018] [Indexed: 11/28/2022] Open
Abstract
Most bacteria swim in liquid environments by rotating one or several flagella. The long external filament of the flagellum is connected to a membrane-embedded basal body by a flexible universal joint, the hook, which allows the transmission of motor torque to the filament. The length of the hook is controlled on a nanometer scale by a sophisticated molecular ruler mechanism. However, why its length is stringently controlled has remained elusive. We engineered and studied a diverse set of hook-length variants of Salmonella enterica. Measurements of plate-assay motility, single-cell swimming speed, and directional persistence in quasi-2D and population-averaged swimming speed and body angular velocity in 3D revealed that the motility performance is optimal around the wild-type hook length. We conclude that too-short hooks may be too stiff to function as a junction and too-long hooks may buckle and create instability in the flagellar bundle. Accordingly, peritrichously flagellated bacteria move most efficiently as the distance travelled per body rotation is maximal and body wobbling is minimized. Thus, our results suggest that the molecular ruler mechanism evolved to control flagellar hook growth to the optimal length consistent with efficient bundle formation. The hook-length control mechanism is therefore a prime example of how bacteria evolved elegant but robust mechanisms to maximize their fitness under specific environmental constraints. Many bacteria use flagella for directed movement in liquid environments. The flexible hook connects the membrane-embedded basal body of the flagellum to the long, external filament. Flagellar function relies on self-assembly processes that define or self-limit the lengths of major parts. The length of the hook is precisely controlled on a nanometer scale by a molecular ruler mechanism. However, the physiological benefit of tight hook-length control remains unclear. Here, we show that the molecular ruler mechanism evolved to control the optimal length of the flagellar hook, which is consistent with efficient motility performance. These results highlight the evolutionary forces that enable flagellated bacteria to optimize their fitness in diverse environments and might have important implications for the design of swimming microrobots.
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Affiliation(s)
- Imke Spöring
- Institute for Biology – Bacterial Physiology, Humboldt-Universität zu Berlin, Berlin, Germany
- Junior Research Group Infection Biology of Salmonella, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Vincent A. Martinez
- School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom
| | - Christian Hotz
- Department of Medicine/MED3 – Pharmacology, University of Fribourg, Fribourg, Switzerland
| | - Jana Schwarz-Linek
- School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom
| | - Keara L. Grady
- Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, United States of America
| | - Josué M. Nava-Sedeño
- Braunschweig Integrated Centre of Systems Biology (BRICS), Braunschweig, Germany
| | - Teun Vissers
- School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom
| | - Hanna M. Singer
- Department of Medicine/MED3 – Microbiologie, University of Fribourg, Fribourg, Switzerland
| | - Manfred Rohde
- Central Facility for Microscopy, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Carole Bourquin
- Department of Medicine/MED3 – Pharmacology, University of Fribourg, Fribourg, Switzerland
- School of Pharmaceutical Sciences, University of Geneva, University of Lausanne, Switzerland
| | - Haralampos Hatzikirou
- Braunschweig Integrated Centre of Systems Biology (BRICS), Braunschweig, Germany
- Systems Immunology, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Wilson C. K. Poon
- School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom
| | - Yann S. Dufour
- Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, United States of America
| | - Marc Erhardt
- Institute for Biology – Bacterial Physiology, Humboldt-Universität zu Berlin, Berlin, Germany
- Junior Research Group Infection Biology of Salmonella, Helmholtz Centre for Infection Research, Braunschweig, Germany
- Department of Medicine/MED3 – Microbiologie, University of Fribourg, Fribourg, Switzerland
- * E-mail:
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24
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Minamino T. Hierarchical protein export mechanism of the bacterial flagellar type III protein export apparatus. FEMS Microbiol Lett 2018; 365:4993518. [DOI: 10.1093/femsle/fny117] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 05/04/2018] [Indexed: 12/18/2022] Open
Affiliation(s)
- Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
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25
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Kinoshita M, Aizawa SI, Inoue Y, Namba K, Minamino T. The role of intrinsically disordered C-terminal region of FliK in substrate specificity switching of the bacterial flagellar type III export apparatus. Mol Microbiol 2017; 105:572-588. [PMID: 28557186 DOI: 10.1111/mmi.13718] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/24/2017] [Indexed: 01/06/2023]
Abstract
The bacterial flagellar export switching machinery consists of a ruler protein, FliK, and an export switch protein, FlhB and switches substrate specificity of the flagellar type III export apparatus upon completion of hook assembly. An interaction between the C-terminal domain of FliK (FliKC ) and the C-terminal cytoplasmic domain of FlhB (FlhBC ) is postulated to be responsible for this switch. FliKC has a compactly folded domain termed FliKT3S4 (residues 268-352) and an intrinsically disordered region composed of the last 53 residues, FliKCT (residues 353-405). Residues 301-350 of FliKT3S4 and the last five residues of FliKCT are critical for the switching function of FliK. FliKCT is postulated to regulate the interaction of FliKT3S4 with FlhBC , but it remains unknown how. Here we report the role of FliKCT in the export switching mechanism. Systematic deletion analyses of FliKCT revealed that residues of 351-370 are responsible for efficient switching of substrate specificity of the export apparatus. Suppressor mutant analyses showed that FliKCT coordinates FliKT3S4 action with the switching. Site-directed photo-cross-linking experiments showed that Val-302 and Ile-304 in the hydrophobic core of FliKT3S4 bind to FlhBC . We propose that FliKCT may induce conformational rearrangements of FliKT3S4 to bind to FlhBC .
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Affiliation(s)
- Miki Kinoshita
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Shin-Ichi Aizawa
- Department of Life Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima, 727-0023, Japan
| | - Yumi Inoue
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.,Quantitative Biology Center, RIKEN, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan
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26
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Hiraoka KD, Morimoto YV, Inoue Y, Fujii T, Miyata T, Makino F, Minamino T, Namba K. Straight and rigid flagellar hook made by insertion of the FlgG specific sequence into FlgE. Sci Rep 2017; 7:46723. [PMID: 28429800 PMCID: PMC5399456 DOI: 10.1038/srep46723] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 03/28/2017] [Indexed: 11/09/2022] Open
Abstract
The bacterial flagellar hook connects the helical flagellar filament to the rotary motor at its base. Bending flexibility of the hook allows the helical filaments to form a bundle behind the cell body to produce thrust for bacterial motility. The hook protein FlgE shows considerable sequence and structural similarities to the distal rod protein FlgG; however, the hook is supercoiled and flexible as a universal joint whereas the rod is straight and rigid as a drive shaft. A short FlgG specific sequence (GSS) has been postulated to confer the rigidity on the FlgG rod, and insertion of GSS at the position between Phe-42 and Ala-43 of FlgE actually made the hook straight. However, it remains unclear whether inserted GSS confers the rigidity as well. Here, we provide evidence that insertion of GSS makes the hook much more rigid. The GSS insertion inhibited flagellar bundle formation behind the cell body, thereby reducing motility. This indicates that the GSS insertion markedly reduced the bending flexibility of the hook. Therefore, we propose that the inserted GSS makes axial packing interactions of FlgE subunits much tighter in the hook to suppress axial compression and extension of the protofilaments required for bending flexibility.
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Affiliation(s)
- Koichi D Hiraoka
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Yusuke V Morimoto
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.,Riken Quantitative Biology Center, 1-3 Yamadoaka, Suita, Osaka 565-0871, Japan
| | - Yumi Inoue
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Takashi Fujii
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Tomoko Miyata
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Fumiaki Makino
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.,Riken Quantitative Biology Center, 1-3 Yamadoaka, Suita, Osaka 565-0871, Japan
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27
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Renault TT, Abraham AO, Bergmiller T, Paradis G, Rainville S, Charpentier E, Guet CC, Tu Y, Namba K, Keener JP, Minamino T, Erhardt M. Bacterial flagella grow through an injection-diffusion mechanism. eLife 2017; 6. [PMID: 28262091 PMCID: PMC5386592 DOI: 10.7554/elife.23136] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Accepted: 03/04/2017] [Indexed: 11/30/2022] Open
Abstract
The bacterial flagellum is a self-assembling nanomachine. The external flagellar filament, several times longer than a bacterial cell body, is made of a few tens of thousands subunits of a single protein: flagellin. A fundamental problem concerns the molecular mechanism of how the flagellum grows outside the cell, where no discernible energy source is available. Here, we monitored the dynamic assembly of individual flagella using in situ labelling and real-time immunostaining of elongating flagellar filaments. We report that the rate of flagellum growth, initially ∼1,700 amino acids per second, decreases with length and that the previously proposed chain mechanism does not contribute to the filament elongation dynamics. Inhibition of the proton motive force-dependent export apparatus revealed a major contribution of substrate injection in driving filament elongation. The combination of experimental and mathematical evidence demonstrates that a simple, injection-diffusion mechanism controls bacterial flagella growth outside the cell. DOI:http://dx.doi.org/10.7554/eLife.23136.001 Most bacteria are able to move in a directed manner towards nutrients or other locations of interest. Many move by rotating long tail-like filaments called flagella that stick out from the cell. The flagellum is a remarkably complex nanomachine. It is several times longer than the main body of the bacterial cell body and its external filament is made of thousands of building blocks of a single protein called flagellin. This protein is made inside the cell and a structure at the base of the flagellum known as a type III secretion system uses chemical energy to pump it out of the cell so that it can be incorporated into the growing flagellum. The exported building blocks travel through a narrow channel within the flagellum and self-assemble at the tip. It has been a mystery for several decades how bacteria manage to assemble the building blocks of flagella outside of the cell, where no discernible energy source is available. Renault et al. used mathematical modeling, biochemical and microscopy techniques to observe how the flagella of a bacterium called Salmonella enterica assemble in real time. The experiments demonstrate that simple biophysical principles regulate the assembly of the flagellum. The building blocks are pumped into the channel of the flagellum by the type III secretion system and then diffuse to the tip of the filament. Accordingly, the longer the flagellum gets, the slower it grows. This molecular mechanism also explains why the growth of bacterial flagella will eventually stop even without any other control mechanisms in place. Further work will be needed to understand how the type III secretion system harnesses chemical energy to drive the movement of flagellin out of the cell into the growing flagellum. A molecular understanding of these processes will aid the design of new antibiotics targeted against type III secretion systems. DOI:http://dx.doi.org/10.7554/eLife.23136.002
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Affiliation(s)
- Thibaud T Renault
- Junior Research Group, Infection Biology of Salmonella, Helmholtz Centre for Infection Research, Braunschweig, Germany.,Max Planck Institute for Infection Biology, Berlin, Germany
| | - Anthony O Abraham
- Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
| | - Tobias Bergmiller
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Guillaume Paradis
- Department of Physics, Engineering Physics and Optics, Laval University, Quebec City, Quebec, Canada
| | - Simon Rainville
- Department of Physics, Engineering Physics and Optics, Laval University, Quebec City, Quebec, Canada
| | | | - Călin C Guet
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Yuhai Tu
- IBM Thomas J Watson Research Center, New York, United States
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan.,RIKEN Quantitative Biology Center, Suita, Japan
| | - James P Keener
- Department of Mathematics, University of Utah, Salt Lake City, United States
| | - Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
| | - Marc Erhardt
- Junior Research Group, Infection Biology of Salmonella, Helmholtz Centre for Infection Research, Braunschweig, Germany
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28
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Gaytán MO, Martínez-Santos VI, Soto E, González-Pedrajo B. Type Three Secretion System in Attaching and Effacing Pathogens. Front Cell Infect Microbiol 2016; 6:129. [PMID: 27818950 PMCID: PMC5073101 DOI: 10.3389/fcimb.2016.00129] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Accepted: 09/27/2016] [Indexed: 02/06/2023] Open
Abstract
Enteropathogenic Escherichia coli and enterohemorrhagic E. coli are diarrheagenic bacterial human pathogens that cause severe gastroenteritis. These enteric pathotypes, together with the mouse pathogen Citrobacter rodentium, belong to the family of attaching and effacing pathogens that form a distinctive histological lesion in the intestinal epithelium. The virulence of these bacteria depends on a type III secretion system (T3SS), which mediates the translocation of effector proteins from the bacterial cytosol into the infected cells. The core architecture of the T3SS consists of a multi-ring basal body embedded in the bacterial membranes, a periplasmic inner rod, a transmembrane export apparatus in the inner membrane, and cytosolic components including an ATPase complex and the C-ring. In addition, two distinct hollow appendages are assembled on the extracellular face of the basal body creating a channel for protein secretion: an approximately 23 nm needle, and a filament that extends up to 600 nm. This filamentous structure allows these pathogens to get through the host cells mucus barrier. Upon contact with the target cell, a translocation pore is assembled in the host membrane through which the effector proteins are injected. Assembly of the T3SS is strictly regulated to ensure proper timing of substrate secretion. The different type III substrates coexist in the bacterial cytoplasm, and their hierarchical secretion is determined by specialized chaperones in coordination with two molecular switches and the so-called sorting platform. In this review, we present recent advances in the understanding of the T3SS in attaching and effacing pathogens.
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Affiliation(s)
- Meztlli O Gaytán
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Verónica I Martínez-Santos
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Eduardo Soto
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Bertha González-Pedrajo
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
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29
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Diepold A, Armitage JP. Type III secretion systems: the bacterial flagellum and the injectisome. Philos Trans R Soc Lond B Biol Sci 2016; 370:rstb.2015.0020. [PMID: 26370933 DOI: 10.1098/rstb.2015.0020] [Citation(s) in RCA: 138] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The flagellum and the injectisome are two of the most complex and fascinating bacterial nanomachines. At their core, they share a type III secretion system (T3SS), a transmembrane export complex that forms the extracellular appendages, the flagellar filament and the injectisome needle. Recent advances, combining structural biology, cryo-electron tomography, molecular genetics, in vivo imaging, bioinformatics and biophysics, have greatly increased our understanding of the T3SS, especially the structure of its transmembrane and cytosolic components, the transcriptional, post-transcriptional and functional regulation and the remarkable adaptivity of the system. This review aims to integrate these new findings into our current knowledge of the evolution, function, regulation and dynamics of the T3SS, and to highlight commonalities and differences between the two systems, as well as their potential applications.
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Affiliation(s)
- Andreas Diepold
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Judith P Armitage
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
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30
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Abstract
The cell represents a highly organized state of living matter in which numerous geometrical parameters are under dynamic regulation in order to match the form of a cell with its function. Cells appear capable of regulating not only the total quantity of their internal organelles, but also the size and number of those organelles. The regulation of three parameters, size, number, and total quantity, can in principle be accomplished by regulating the production or growth of organelles, their degradation or disassembly, and their partitioning among daughter cells during division. Any or all of these steps could in principle be under regulation. But if organelle assembly or disassembly is regulated by number or size, how would the cell know how many copies of an organelle it has, or how big they are?
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Affiliation(s)
- Wallace F Marshall
- Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143;
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31
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Nariya MK, Israeli J, Shi JJ, Deeds EJ. Mathematical Model for Length Control by the Timing of Substrate Switching in the Type III Secretion System. PLoS Comput Biol 2016; 12:e1004851. [PMID: 27078235 PMCID: PMC4831731 DOI: 10.1371/journal.pcbi.1004851] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 03/06/2016] [Indexed: 12/28/2022] Open
Abstract
Type III Secretion Systems (T3SS) are complex bacterial structures that provide gram-negative pathogens with a unique virulence mechanism whereby they grow a needle-like structure in order to inject bacterial effector proteins into the cytoplasm of a host cell. Numerous experiments have been performed to understand the structural details of this nanomachine during the past decade. Despite the concerted efforts of molecular and structural biologists, several crucial aspects of the assembly of this structure, such as the regulation of the length of the needle itself, remain unclear. In this work, we used a combination of mathematical and computational techniques to better understand length control based on the timing of substrate switching, which is a possible mechanism for how bacteria ensure that the T3SS needles are neither too short nor too long. In particular, we predicted the form of the needle length distribution based on this mechanism, and found excellent agreement with available experimental data from Salmonella typhimurium with only a single free parameter. Although our findings provide preliminary evidence in support of the substrate switching model, they also make a set of quantitative predictions that, if tested experimentally, would assist in efforts to unambiguously characterize the regulatory mechanisms that control the growth of this crucial virulence factor.
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Affiliation(s)
- Maulik K. Nariya
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas, United States of America
| | - Johnny Israeli
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas, United States of America
| | - Jack J. Shi
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas, United States of America
| | - Eric J. Deeds
- Center for Computational Biology, University of Kansas, Lawrence, Kansas, United States of America
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, United States of America
- Sante Fe Institute, Santa Fe, New Mexico, United States of America
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32
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Identification of the Key Sequence in the FliK C-Terminal Domain for Substrate Specificity Switching in the Flagellar Protein Secretion. J Bacteriol 2015; 198:410-5. [PMID: 26527646 DOI: 10.1128/jb.00712-15] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 10/28/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The flagellar hook is a short tubular structure located between the external filament and the membrane-bound basal body. The average hook length is 55 nm and is determined by the soluble protein FliK and the integral membrane protein FlhB. Hook elongation is terminated by FliK-mediated cessation of hook protein secretion, followed by the secretion of filamentous proteins. This process is referred to as the substrate specificity switch. Switching of the secretion modes results from a direct interaction between the FliK C-terminal domain (FliKC) and the secretion gate in FlhB. FliKC consists of two α-helices and four β-strands. Loop 2 connects the first two β-sheets and contains a conserved sequence of 9 residues. Genetic and physiological analyses of various fliK partial deletion mutants pointed to loop 2 as essential for induction of a conformational change in the FlhB gate. We constructed single-amino-acid substitutions in the conserved region of loop 2 of FliK and discovered that the loop sequence LRL is essential for the timely switching of secretion modes. IMPORTANCE Flagellar protein secretion is controlled by the soluble protein FliK. We discovered that the loop 2 sequence LRL in the FliK C terminus was essential for timely switching of secretion modes. This mechanism is applicable to type three secretions systems that secrete virulence factors in bacterial pathogens.
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33
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Marshall WF. How Cells Measure Length on Subcellular Scales. Trends Cell Biol 2015; 25:760-768. [PMID: 26437596 DOI: 10.1016/j.tcb.2015.08.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Revised: 08/21/2015] [Accepted: 08/24/2015] [Indexed: 02/06/2023]
Abstract
Cells are not just amorphous bags of enzymes, but precise and complex machines. With any machine, it is important that the parts be of the right size, yet our understanding of the mechanisms that control size of cellular structures remains at a rudimentary level in most cases. One problem with studying size control is that many cellular organelles have complex 3D structures that make their size hard to measure. Here we focus on linear structures within cells, for which the problem of size control reduces to the problem of length control. We compare and contrast potential mechanisms for length control to understand how cells solve simple geometry problems.
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Affiliation(s)
- Wallace F Marshall
- Department of Biochemistry and Biophysics, Center for Systems and Synthetic Biology, University of California San Francisco, 600 16th Street, San Francisco, CA 94158, USA.
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34
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Minamino T. [Structure and function of the bacterial flagellar type III protein export system in Salmonella
]. Nihon Saikingaku Zasshi 2015; 70:351-64. [PMID: 26310179 DOI: 10.3412/jsb.70.351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The bacterial flagellum is a filamentous organelle that propels the bacterial cell body in liquid media. For construction of the bacterial flagellum beyond the cytoplasmic membrane, flagellar component proteins are transported by its specific protein export apparatus from the cytoplasm to the distal end of the growing flagellar structure. The flagellar export apparatus consists of a transmembrane export gate complex and a cytoplasmic ATPase ring complex. Flagellar substrate-specific chaperones bind to their cognate substrates in the cytoplasm and escort the substrates to the docking platform of the export gate. The export apparatus utilizes ATP and proton motive force across the cytoplasmic membrane as the energy sources to drive protein export and coordinates protein export with assembly by ordered export of substrates to parallel with their order of assembly. In this review, we summarize our current understanding of the structure and function of the flagellar protein export system in Salmonella enterica serovar Typhimurium.
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Affiliation(s)
- Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University
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35
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Structural Characterization of the Fla2 Flagellum of Rhodobacter sphaeroides. J Bacteriol 2015; 197:2859-66. [PMID: 26124240 DOI: 10.1128/jb.00170-15] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Accepted: 06/08/2015] [Indexed: 01/19/2023] Open
Abstract
UNLABELLED Rhodobacter sphaeroides is a free-living alphaproteobacterium that contains two clusters of functional flagellar genes in its genome: one acquired by horizontal gene transfer (fla1) and one that is endogenous (fla2). We have shown that the Fla2 system is normally quiescent and under certain conditions produces polar flagella, while the Fla1 system is always active and produces a single flagellum at a nonpolar position. In this work we purified and characterized the structure and analyzed the composition of the Fla2 flagellum. The number of polar filaments per cell is 4.6 on average. By comparison with the Fla1 flagellum, the prominent features of the ultra structure of the Fla2 HBB are the absence of an H ring, thick and long hooks, and a smoother zone at the hook-filament junction. The Fla2 helical filaments have a pitch of 2.64 μm and a diameter of 1.4 μm, which are smaller than those of the Fla1 filaments. Fla2 filaments undergo polymorphic transitions in vitro and showed two polymorphs: curly (right-handed) and coiled. However, in vivo in free-swimming cells, we observed only a bundle of filaments, which should probably be left-handed. Together, our results indicate that Fla2 cell produces multiple right-handed polar flagella, which are not conventional but exceptional. IMPORTANCE R. sphaeroides possesses two functional sets of flagellar genes. The fla1 genes are normally expressed in the laboratory and were acquired by horizontal transfer. The fla2 genes are endogenous and are expressed in a Fla1(-) mutant grown phototrophically and in the absence of organic acids. The Fla1 system produces a single lateral or subpolar flagellum, and the Fla2 system produces multiple polar flagella. The two kinds of flagella are never expressed simultaneously, and both are used for swimming in liquid media. The two sets of genes are certainly ready for responding to specific environmental conditions. The characterization of the Fla2 system will help us to understand its role in the physiology of this microorganism.
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36
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Molecular ruler determines needle length for the Salmonella Spi-1 injectisome. Proc Natl Acad Sci U S A 2015; 112:4098-103. [PMID: 25775540 DOI: 10.1073/pnas.1423492112] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The type-III secretion (T3S) systems of bacteria are part of self-assembling nanomachines: the bacterial flagellum that enables cells to propel themselves through liquid and across hydrated surfaces, and the injectisome that delivers pathogenic effector proteins into eukaryotic host cells. Although the flagellum and injectisome serve different purposes, they are evolutionarily related and share many structural similarities. Core features to these T3S systems are intrinsic length control mechanisms for external cellular projections: the hook of the flagellum and the injectisome needle. We present evidence that the Spi-1 injectisome, like the Salmonella flagellar hook, uses a secreted molecular ruler, InvJ, to determine needle length. This result supports a universal length control mechanism using molecular rulers for T3S systems.
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37
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Kodera N, Uchida K, Ando T, Aizawa SI. Two-ball structure of the flagellar hook-length control protein FliK as revealed by high-speed atomic force microscopy. J Mol Biol 2014; 427:406-14. [PMID: 25463436 DOI: 10.1016/j.jmb.2014.11.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 10/15/2014] [Accepted: 11/10/2014] [Indexed: 01/13/2023]
Abstract
The bacterial flagellar hook is a short and uniquely curved tube that connects the basal body to the filament. Hook length is controlled at 55 nm on average by a soluble protein FliK in Salmonella enterica serovar Typhimurium. The N-terminal segment of FliK responsible for measuring the hook length is considered to be intrinsically disordered. Here, we show by high-speed atomic force microscopy that a FliK molecule in solution takes on a shape of two balls linked by a flexible string; the larger ball corresponds to the N-terminal region and the smaller one corresponds to the C-terminal region. The N-terminal domain is stable but the C-terminal domain fluctuates in shape. Based on these and other features of FliK, we propose that the folding of the N-terminal segment at the tip of the growing hook plays a major role in determining the minimal length of the hook.
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Affiliation(s)
- Noriyuki Kodera
- Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa 920-1192, Japan
| | - Kaoru Uchida
- Department of Life Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan
| | - Toshio Ando
- Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa 920-1192, Japan; Department of Physics, Kanazawa University, Kanazawa 920-1192, Japan.
| | - Shin-Ichi Aizawa
- Department of Life Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan.
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38
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Abstract
Bacterial flagellar motility is among the most extensively studied physiological systems in biology, but most research has been restricted to using the highly similar Gram-negative species Escherichia coli and Salmonella enterica. Here, we review the recent advances in the study of flagellar structure and regulation of the distantly related and genetically tractable Gram-positive bacterium Bacillus subtilis. B. subtilis has a thicker layer of peptidoglycan and lacks the outer membrane of the Gram-negative bacteria; thus, not only phylogenetic separation but also differences in fundamental cell architecture contribute to deviations in flagellar structure and regulation. We speculate that a large number of flagella and the absence of a periplasm make B. subtilis a premier organism for the study of the earliest events in flagellar morphogenesis and the type III secretion system. Furthermore, B. subtilis has been instrumental in the study of heterogeneous gene transcription in subpopulations and of flagellar regulation at the translational and functional level.
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39
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The flagellar soluble protein FliK determines the minimal length of the hook in Salmonella enterica serovar Typhimurium. J Bacteriol 2014; 196:1753-8. [PMID: 24563036 DOI: 10.1128/jb.00050-14] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The length of the flagellar hook is controlled by the soluble protein FliK. FliK is structurally divided into two halves with distinct functions; the N-terminal half determines hook length, while the C-terminal half switches the secretion substrate specificity, consequently terminating hook elongation. FliK properly achieves both functions only when it is secreted. In a previous paper, we showed that a temperature-sensitive flgE mutant of Salmonella enterica serovar Typhimurium, SJW2219, produced basal bodies with short hooks (average length, 25 nm) at 37°C. In this study, we show that the mutant cells grown at 37°C secrete FliK but not flagellin (FliC), indicating that FliK is abortively secreted into the medium when the hook is shorter than 30 nm. In contrast, FliK unfailingly switches the gate modes when the hook is longer than 30 nm. Taking the FliC, FliK, and FlgM secretion patterns into account, we conclude that FliK determines the minimal length of the hook. We will discuss how FliK detects the critical switching point of the secretion gate.
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40
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Diepold A, Wagner S. Assembly of the bacterial type III secretion machinery. FEMS Microbiol Rev 2014; 38:802-22. [PMID: 24484471 DOI: 10.1111/1574-6976.12061] [Citation(s) in RCA: 113] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2013] [Revised: 01/02/2014] [Accepted: 01/13/2014] [Indexed: 11/29/2022] Open
Abstract
Many bacteria that live in contact with eukaryotic hosts, whether as symbionts or as pathogens, have evolved mechanisms that manipulate host cell behaviour to their benefit. One such mechanism, the type III secretion system, is employed by Gram-negative bacterial species to inject effector proteins into host cells. This function is reflected by the overall shape of the machinery, which resembles a molecular syringe. Despite the simplicity of the concept, the type III secretion system is one of the most complex known bacterial nanomachines, incorporating one to more than hundred copies of up to twenty different proteins into a multi-MDa transmembrane complex. The structural core of the system is the so-called needle complex that spans the bacterial cell envelope as a tripartite ring system and culminates in a needle protruding from the bacterial cell surface. Substrate targeting and translocation are accomplished by an export machinery consisting of various inner membrane embedded and cytoplasmic components. The formation of such a multimembrane-spanning machinery is an intricate task that requires precise orchestration. This review gives an overview of recent findings on the assembly of type III secretion machines, discusses quality control and recycling of the system and proposes an integrated assembly model.
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Affiliation(s)
- Andreas Diepold
- Department of Biochemistry, University of Oxford, Oxford, UK
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41
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Cherradi Y, Hachani A, Allaoui A. Spa13 of Shigella flexneri has a dual role: chaperone escort and export gate-activator switch of the type III secretion system. Microbiology (Reading) 2014; 160:130-141. [DOI: 10.1099/mic.0.071712-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The type III secretion apparatus (T3SA) is used by numerous Gram-negative pathogens to inject virulence factors into eukaryotic cells. The Shigella flexneri T3SA spans the bacterial envelope and its assembly requires the products of ~20 mxi and spa genes. Despite progress made in understanding how the T3SA is assembled, the role of several predicted soluble components, such as Spa13, remains elusive. Here, we show that the secretion defect of the spa13 mutant is associated with lack of T3SA assembly which is partly due to the instability of the needle component MxiH. In contrast to its Yersinia counterpart, Spa13 is not a secreted protein. We identified a network of interactions between Spa13 and the ATPase Spa47, the C-ring protein Spa33, and the inner-membrane protein Spa40. Moreover, we revealed a Spa13 interaction with the inner-membrane MxiA and showed that overexpression of the large cytoplasmic domain of MxiA in the WT background shuts off secretion. Lastly, we demonstrated that Spa13 interacts with the cleaved form of Spa40 and with the translocator chaperone IpgC, suggesting that Spa13 intervenes during the secretion hierarchy switch process. Collectively, our results support a dual role of Spa13 as a chaperone escort and as an export gate-activator switch.
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Affiliation(s)
- Youness Cherradi
- Laboratoire de Bactériologie Moléculaire, Faculté de Médecine, Université Libre de Bruxelles, Route de Lennik, 808, 1070 Bruxelles, Belgium
| | - Abderrahman Hachani
- Laboratoire de Bactériologie Moléculaire, Faculté de Médecine, Université Libre de Bruxelles, Route de Lennik, 808, 1070 Bruxelles, Belgium
| | - Abdelmounaaïm Allaoui
- Laboratoire de Bactériologie Moléculaire, Faculté de Médecine, Université Libre de Bruxelles, Route de Lennik, 808, 1070 Bruxelles, Belgium
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42
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Minamino T. Protein export through the bacterial flagellar type III export pathway. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1843:1642-8. [PMID: 24064315 DOI: 10.1016/j.bbamcr.2013.09.005] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Accepted: 09/10/2013] [Indexed: 01/02/2023]
Abstract
For construction of the bacterial flagellum, which is responsible for bacterial motility, the flagellar type III export apparatus utilizes both ATP and proton motive force across the cytoplasmic membrane and exports flagellar proteins from the cytoplasm to the distal end of the nascent structure. The export apparatus consists of a membrane-embedded export gate made of FlhA, FlhB, FliO, FliP, FliQ, and FliR and a water-soluble ATPase ring complex consisting of FliH, FliI, and FliJ. FlgN, FliS, and FliT act as substrate-specific chaperones that do not only protect their cognate substrates from degradation and aggregation in the cytoplasm but also efficiently transfer the substrates to the export apparatus. The ATPase ring complex facilitates the initial entry of the substrates into the narrow pore of the export gate. The export gate by itself is a proton-protein antiporter that uses the two components of proton motive force, the electric potential difference and the proton concentration difference, for different steps of the export process. A specific interaction of FlhA with FliJ located in the center of the ATPase ring complex allows the export gate to efficiently use proton motive force to drive protein export. The ATPase ring complex couples ATP binding and hydrolysis to its assembly-disassembly cycle for rapid and efficient protein export cycle. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
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Affiliation(s)
- Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.
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43
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Chaperone-protein interactions that mediate assembly of the bacteriophage lambda tail to the correct length. J Mol Biol 2013; 426:1004-18. [PMID: 23911548 DOI: 10.1016/j.jmb.2013.06.040] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Revised: 06/21/2013] [Accepted: 06/30/2013] [Indexed: 11/22/2022]
Abstract
Bacteriophage λ makes two proteins with overlapping amino acid sequences that are essential for tail assembly. These two proteins, gpG and gpGT, are related by a programmed translational frameshift that is conserved among diverse phages and functions in λ to ensure that gpG and the frameshift product gpGT are made in a molar ratio of approximately 30:1. Although both proteins are required and must be present in the correct ratio for assembly of functional tails, neither is present in mature tails. During λ tail assembly, major tail protein gpV polymerizes to form a long tube whose length is controlled by the tape measure protein gpH. We show that the "G" domains of gpG and gpGT bind to all or parts of tail length tape measure protein gpH and that the "T" domain of gpGT binds to major tail shaft subunit gpV, and present a model for how gpG and gpGT chaperone gpH and direct the polymerization of gpV to form a tail of the correct length.
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Length control of the flagellar hook in a temperature-sensitive flgE mutant of Salmonella enterica serovar Typhimurium. J Bacteriol 2013; 195:3590-5. [PMID: 23749974 DOI: 10.1128/jb.00302-13] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The flagellar hook is a short, curved, extracellular structure located between the basal body and the filament. The hook is composed of the FlgE protein. In this study, we analyzed flagellum assembly in a temperature-sensitive flgE mutant of Salmonella enterica serovar Typhimurium. When the mutant cells were grown at 30°C, they produced flagella of a normal length (71% of the population) and short hooks without filaments (26%). At 37°C, 70% of the basal bodies lacked hooks, and intact flagella made up only 6% of the population. Mutant cells secreted monomeric FlgE in abundance at 37°C, suggesting that the mutant FlgE protein might be defective in polymerization at higher temperatures. The average length of the hooks in intact filaments was 55 nm, whereas after acid treatment, it was 45 nm. SDS-PAGE analysis of the hook-basal body showed that HAP1 was missing in the mutant but not in the wild type. We concluded that hook length in the mutant is controlled in the same way as in the wild type, but the hook appeared short after acid treatment due to the lack of HAP1. We also learned that the true length of the hook is possibly 45 nm, not 55 nm, as has been believed.
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Moriya N, Minamino T, Ferris HU, Morimoto YV, Ashihara M, Kato T, Namba K. Role of the Dc domain of the bacterial hook protein FlgE in hook assembly and function. Biophysics (Nagoya-shi) 2013; 9:63-72. [PMID: 27493542 PMCID: PMC4629672 DOI: 10.2142/biophysics.9.63] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Accepted: 05/07/2013] [Indexed: 12/01/2022] Open
Abstract
The bacterial flagellar hook acts as a universal joint to smoothly transmit torque produced by the motor to the filament. The hook protein FlgE assembles into a 55 nm tubular structure with the help of the hook cap (FlgD). FlgE consists of four domains, D0, Dc, D1 and D2, arranged from the inner to the outer part of the tubular structure of the hook. The Dc domain contributes to the structural stability of the hook, but it is unclear how this Dc domain is responsible for the universal joint mechanism. Here, we carried out a deletion analysis of the FlgE Dc domain. FlgEΔ4/5 with deletion of residues 30 to 49 was not secreted into the culture media. FlgEΔ5 and FlgEΔ6 with deletions of residues 40 to 49 and 50 to 59, respectively, still formed hooks, allowing the export apparatus to export the hook-filament junction proteins FlgK and FlgL and flagellin FliC. However, these deletions inhibited the replacement of the FlgD hook cap by FlgK at the hook tip, thereby abolishing filament formation. Deletion of residues 50 to 59 significantly affected hook morphology. These results suggest that the Dc domain is responsible not only for hook assembly but also for FlgE export, the interaction with FlgK, and the polymorphic supercoiling mechanism of the hook.
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Affiliation(s)
- Nao Moriya
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Tohru Minamino
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Hedda U Ferris
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA
| | - Yusuke V Morimoto
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan; Riken Quantitative Biology Center, 1-3 Yamadoaka, Suita, Osaka 565-0871, Japan
| | - Masamichi Ashihara
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Takayuki Kato
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan; Riken Quantitative Biology Center, 1-3 Yamadoaka, Suita, Osaka 565-0871, Japan
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Guttenplan SB, Shaw S, Kearns DB. The cell biology of peritrichous flagella in Bacillus subtilis. Mol Microbiol 2012. [PMID: 23190039 DOI: 10.1111/mmi.12103] [Citation(s) in RCA: 110] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Bacterial flagella are highly conserved molecular machines that have been extensively studied for assembly, function and gene regulation. Less studied is how and why bacteria differ based on the number and arrangement of the flagella they synthesize. Here we explore the cell biology of peritrichous flagella in the model bacterium Bacillus subtilis by fluorescently labelling flagellar basal bodies, hooks and filaments. We find that the average B. subtilis cell assembles approximately 26 flagellar basal bodies and we show that basal body number is controlled by SwrA. Basal bodies are assembled rapidly (< 5 min) but the assembly of flagella capable of supporting motility is rate limited by filament polymerization (> 40 min). We find that basal bodies are not positioned randomly on the cell surface. Rather, basal bodies occupy a grid-like pattern organized symmetrically around the midcell and that flagella are discouraged at the poles. Basal body position is genetically determined by FlhF and FlhG homologues to control spatial patterning differently from what is seen in bacteria with polar flagella. Finally, spatial control of flagella in B. subtilis seems more relevant to the inheritance of flagella and motility of individual cells than the motile behaviour of populations.
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Protein export according to schedule: architecture, assembly, and regulation of type III secretion systems from plant- and animal-pathogenic bacteria. Microbiol Mol Biol Rev 2012; 76:262-310. [PMID: 22688814 DOI: 10.1128/mmbr.05017-11] [Citation(s) in RCA: 299] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Flagellar and translocation-associated type III secretion (T3S) systems are present in most gram-negative plant- and animal-pathogenic bacteria and are often essential for bacterial motility or pathogenicity. The architectures of the complex membrane-spanning secretion apparatuses of both systems are similar, but they are associated with different extracellular appendages, including the flagellar hook and filament or the needle/pilus structures of translocation-associated T3S systems. The needle/pilus is connected to a bacterial translocon that is inserted into the host plasma membrane and mediates the transkingdom transport of bacterial effector proteins into eukaryotic cells. During the last 3 to 5 years, significant progress has been made in the characterization of membrane-associated core components and extracellular structures of T3S systems. Furthermore, transcriptional and posttranscriptional regulators that control T3S gene expression and substrate specificity have been described. Given the architecture of the T3S system, it is assumed that extracellular components of the secretion apparatus are secreted prior to effector proteins, suggesting that there is a hierarchy in T3S. The aim of this review is to summarize our current knowledge of T3S system components and associated control proteins from both plant- and animal-pathogenic bacteria.
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Role of EscP (Orf16) in injectisome biogenesis and regulation of type III protein secretion in enteropathogenic Escherichia coli. J Bacteriol 2012; 194:6029-45. [PMID: 22923600 DOI: 10.1128/jb.01215-12] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Enteropathogenic Escherichia coli employs a type III secretion system (T3SS) to translocate virulence effector proteins directly into enterocyte host cells, leading to diarrheal disease. The T3SS is encoded within the chromosomal locus of enterocyte effacement (LEE). The function of some of the LEE-encoded proteins remains unknown. Here we investigated the role of the Orf16 protein in T3SS biogenesis and function. An orf16 deletion mutant showed translocator and effector protein secretion profiles different from those of wild-type cells. The orf16 null strain produced T3S structures with abnormally long needles and filaments that caused weak hemolysis of red blood cells. Furthermore, the number of fully assembled T3SSs was also reduced in the orf16 mutant, indicating that Orf16, though not essential, is required for efficient T3SS assembly. Analysis of protein secretion revealed that Orf16 is a T3SS-secreted substrate and regulates the secretion of the inner rod component EscI. Both pulldown and yeast two-hybrid assays showed that Orf16 interacts with the C-terminal domain of an inner membrane component of the secretion apparatus, EscU; the inner rod protein EscI; the needle protein EscF; and the multieffector chaperone CesT. These results suggest that Orf16 regulates needle length and, along with EscU, participates in a substrate specificity switch from early substrates to translocators. Taken together, our results suggest that Orf16 acts as a molecular measuring device in a way similar to that of members of the Yersinia YscP and flagellar FliK protein family. Therefore, we propose that this protein be renamed EscP.
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50
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