1
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H-NS and ToxT Inversely Control Cholera Toxin Production by Binding to Overlapping DNA Sequences. J Bacteriol 2021; 203:e0018721. [PMID: 34228499 DOI: 10.1128/jb.00187-21] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Vibrio cholerae infects human hosts following ingestion of contaminated food or water, resulting in the severe diarrheal disease cholera. The watery diarrhea that is characteristic of the disease is directly caused by the production of cholera toxin (CT). A complex regulatory cascade controls the production of CT and other virulence factors. However, ultimately, a single protein, ToxT, directly binds to virulence gene promoters and activates their transcription. Previously, we identified two ToxT binding sites, or toxboxes, within the cholera toxin promoter (PctxAB). The toxboxes overlap the two promoter-proximal GATTTTT heptad repeats found within PctxAB in classical biotype V. cholerae strain O395. These heptad repeats were previously found to be located within a large DNA region bound by H-NS, a global transcriptional repressor present in Gram-negative bacteria. The current model for the control of PctxAB transcription proposes complete H-NS displacement from the DNA by ToxT, followed by direct activation by ToxT-RNA polymerase (RNAP) contacts. The goal of this study was to determine more precisely where H-NS binds to PctxAB and test the hypothesis that ToxT completely displaces H-NS from the PctxAB promoter before activating transcription. The results suggest that H-NS binds only to the region of PctxAB encompassing the heptad repeats and that ToxT displaces H-NS only from its most promoter-proximal binding sites, calling for a revision of the current model involving H-NS and ToxT at PctxAB. IMPORTANCE H-NS is a global negative regulator of transcription in Gram-negative bacteria, particularly in horizontally acquired genetic islands. Previous work in Vibrio cholerae suggested that H-NS represses the transcription of cholera toxin genes by binding to a large region upstream of its promoter and that the virulence activator ToxT derepresses transcription by removing H-NS from the promoter. Here, new data support a revised model in which ToxT displaces only H-NS bound to the most promoter-proximal DNA sites that overlap the ToxT binding sites, leaving the upstream sites occupied by H-NS. This introduces a higher-resolution mechanism for the antirepression of H-NS in the control of cholera toxin production.
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2
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Zhao X, Remington JM, Schneebeli ST, Arold ST, Li J. Molecular Basis for Environment Sensing by a Nucleoid-Structuring Bacterial Protein Filament. J Phys Chem Lett 2021; 12:7878-7884. [PMID: 34382809 PMCID: PMC9346976 DOI: 10.1021/acs.jpclett.1c01710] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The histone-like nucleoid structuring (H-NS) protein controls the expression of hundreds of genes in Gram-positive bacteria through its capability to coat and condense DNA. This mechanism requires the formation of superhelical H-NS protein filaments that are sensitive to temperature and salinity, allowing H-NS to act as an environment sensor. We use multiscale modeling and simulations to obtain detailed insights into the mechanism of H-NS filament's sensitivity to environmental changes. Through the simulations of the superhelical H-NS filament, we reveal how different environments induce heterogeneity of H-NS monomers. Further, we observe that transient self-association within the H-NS filament creates temperature-inducible strain and might mildly oppose DNA binding. We also probe different H-NS-DNA complex architectures and show that complexation enhances the stability of both DNA and H-NS superhelices. Overall, our results provide unprecedented molecular insights into the environmental sensing and DNA interactions of a prototypical nucleoid-structuring bacterial protein filament.
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Affiliation(s)
- Xiaochuan Zhao
- Departments of Chemistry and Materials Science, University of Vermont, Burlington VT 05405
| | - Jacob M. Remington
- Departments of Chemistry and Materials Science, University of Vermont, Burlington VT 05405
| | - Severin T. Schneebeli
- Departments of Chemistry and Materials Science, University of Vermont, Burlington VT 05405
| | - Stefan T. Arold
- King Abdullah University of Science and Technology (KAUST), Computational Bioscience Research Center (CBRC), Biological and Environmental Science and Engineering (BESE), Thuwal, 23955-6900, Saudi Arabia
- Centre de Biologie Structurale, CNRS, INSERM, Université de Montpellier, 34090 Montpellier, France
| | - Jianing Li
- Departments of Chemistry and Materials Science, University of Vermont, Burlington VT 05405
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3
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Abstract
Cholera is a potentially lethal disease that is endemic in much of the developing world. Vibrio cholerae, the bacterium underlying the disease, infects humans utilizing proteins encoded on horizontally acquired genetic material. Here, we provide evidence that TsrA, a Vibrionaceae-specific protein, plays a critical role in regulating these genetic elements and is essential for V. cholerae virulence in a mouse intestinal model. Pathogenic strains of Vibrio cholerae require careful regulation of horizontally acquired virulence factors that are largely located on horizontally acquired genomic islands (HAIs). While TsrA, a Vibrionaceae-specific protein, is known to regulate the critical HAI virulence genes toxT and ctxA, its broader function throughout the genome is unknown. Here, we find that deletion of tsrA results in genomewide expression patterns that heavily correlate with those seen upon deletion of hns, a widely conserved bacterial protein that regulates V. cholerae virulence. This correlation is particularly strong for loci on HAIs, where all differentially expressed loci in the ΔtsrA mutant are also differentially expressed in the Δhns mutant. Correlation between TsrA and H-NS function extends to in vivo virulence phenotypes where deletion of tsrA compensates for the loss of ToxR activity in V. cholerae and promotes wild-type levels of mouse intestinal colonization. All in all, we find that TsrA broadly controls V. cholerae infectivity via repression of key HAI virulence genes and many other targets in the H-NS regulon. IMPORTANCE Cholera is a potentially lethal disease that is endemic in much of the developing world. Vibrio cholerae, the bacterium underlying the disease, infects humans utilizing proteins encoded on horizontally acquired genetic material. Here, we provide evidence that TsrA, a Vibrionaceae-specific protein, plays a critical role in regulating these genetic elements and is essential for V. cholerae virulence in a mouse intestinal model.
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4
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Kumar A, Das B, Kumar N. Vibrio Pathogenicity Island-1: The Master Determinant of Cholera Pathogenesis. Front Cell Infect Microbiol 2020; 10:561296. [PMID: 33123494 PMCID: PMC7574455 DOI: 10.3389/fcimb.2020.561296] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 09/11/2020] [Indexed: 11/13/2022] Open
Abstract
Cholera is an acute secretory diarrhoeal disease caused by the bacterium Vibrio cholerae. The key determinants of cholera pathogenicity, cholera toxin (CT), and toxin co-regulated pilus (TCP) are part of the genome of two horizontally acquired Mobile Genetic Elements (MGEs), CTXΦ, and Vibrio pathogenicity island 1 (VPI-1), respectively. Besides, V. cholerae genome harbors several others MGEs that provide antimicrobial resistance, metabolic functions, and other fitness traits. VPI-1, one of the most well characterized genomic island (GI), deserved a special attention, because (i) it encodes many of the virulence factors that facilitate development of cholera (ii) it is essential for the acquisition of CTXΦ and production of CT, and (iii) it is crucial for colonization of V. cholerae in the host intestine. Nevertheless, VPI-1 is ubiquitously present in all the epidemic V. cholerae strains. Therefore, to understand the role of MGEs in the evolution of cholera pathogen from a natural aquatic habitat, it is important to understand the VPI-1 encoded functions, their acquisition and possible mode of dissemination. In this review, we have therefore discussed our present understanding of the different functions of VPI-1 those are associated with virulence, important for toxin production and essential for the disease development.
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Affiliation(s)
- Ashok Kumar
- Translational Health Science and Technology Institute, Faridabad, India.,Centre for Doctoral Studies, Advanced Research Centre, Manipal Academy of Higher Education, Manipal, India
| | - Bhabatosh Das
- Translational Health Science and Technology Institute, Faridabad, India.,Centre for Doctoral Studies, Advanced Research Centre, Manipal Academy of Higher Education, Manipal, India
| | - Niraj Kumar
- Translational Health Science and Technology Institute, Faridabad, India.,Centre for Doctoral Studies, Advanced Research Centre, Manipal Academy of Higher Education, Manipal, India
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5
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Dorman MJ, Dorman CJ. Regulatory Hierarchies Controlling Virulence Gene Expression in Shigella flexneri and Vibrio cholerae. Front Microbiol 2018; 9:2686. [PMID: 30473684 PMCID: PMC6237886 DOI: 10.3389/fmicb.2018.02686] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 10/22/2018] [Indexed: 12/13/2022] Open
Abstract
Gram-negative enteropathogenic bacteria use a variety of strategies to cause disease in the human host and gene regulation in some form is typically a part of the strategy. This article will compare the toxin-based infection strategy used by the non-invasive pathogen Vibrio cholerae, the etiological agent in human cholera, with the invasive approach used by Shigella flexneri, the cause of bacillary dysentery. Despite the differences in the mechanisms by which the two pathogens cause disease, they use environmentally-responsive regulatory hierarchies to control the expression of genes that have some features, and even some components, in common. The involvement of AraC-like transcription factors, the integration host factor, the Factor for inversion stimulation, small regulatory RNAs, the RNA chaperone Hfq, horizontal gene transfer, variable DNA topology and the need to overcome the pervasive silencing of transcription by H-NS of horizontally acquired genes are all shared features. A comparison of the regulatory hierarchies in these two pathogens illustrates some striking cross-species similarities and differences among mechanisms coordinating virulence gene expression. S. flexneri, with its low infectious dose, appears to use a strategy that is centered on the individual bacterial cell, whereas V. cholerae, with a community-based, quorum-dependent approach and an infectious dose that is several orders of magnitude higher, seems to rely more on the actions of a bacterial collective.
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Affiliation(s)
- Matthew J Dorman
- Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, United Kingdom
| | - Charles J Dorman
- Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College Dublin, Dublin, Ireland
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6
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Elgaml A, Miyoshi SI. Role of the Histone-Like Nucleoid Structuring Protein (H-NS) in the Regulation of Virulence Factor Expression and Stress Response in Vibrio vulnificus. Biocontrol Sci 2016; 20:263-74. [PMID: 26699858 DOI: 10.4265/bio.20.263] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Abstract
Temperature is one of the important parameters regulating the expression of virulence factors in bacteria. The global regulator, a histone-like nucleoid structuring protein (H-NS), is known to play a crucial role in this regulation. In the present study, we first clarified the role of H-NS in the temperature-dependent regulation of virulence factor production in Vibrio vulnificus, including that of the cytolytic toxin (V. vulnificus hemolysin: VVH) and the proteolytic enzyme (V. vulnificus protease: VVP). The expression of hns itself was subjected to temperature regulation, where hns was expressed more at 26 ℃ than at 37 ℃. VVH production and the expression of its gene vvhA were increased by disruption of the hns gene. H-NS appeared to affect the vvhA expression by the well-documented transcriptional silencing mechanism. On the other hand, hns disruption resulted in the reduction of VVP production and the expression of its gene vvpE. H-NS was suggested to positively regulate vvpE expression through the increase in the level of the rpoS mRNA. Moreover, H-NS was found to contribute to the survival of V. vulnificus in stressful environments. When compared to the wild type strain, the hns mutant exhibited reduced survival rates when subjected to acidic pH, hyperosmotic and oxidative stress.
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Affiliation(s)
- Abdelaziz Elgaml
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University
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7
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H-NS: an overarching regulator of the Vibrio cholerae life cycle. Res Microbiol 2016; 168:16-25. [PMID: 27492955 DOI: 10.1016/j.resmic.2016.07.007] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 07/22/2016] [Accepted: 07/24/2016] [Indexed: 12/22/2022]
Abstract
Vibrio cholerae has become a model organism for studies connecting virulence, pathogen evolution and infectious disease ecology. The coordinate expression of motility, virulence and biofilm enhances its pathogenicity, environmental fitness and fecal-oral transmission. The histone-like nucleoid structuring protein negatively regulates gene expression at multiple phases of the V. cholerae life cycle. Here we discuss: (i) the regulatory and structural implications of H-NS chromatin-binding in the two-chromosome cholera bacterium; (ii) the factors that counteract H-NS repression; and (iii) a model for the regulation of the V. cholerae life cycle that integrates H-NS repression, cyclic diguanylic acid signaling and the general stress response.
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8
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Wagemans J, Delattre AS, Uytterhoeven B, De Smet J, Cenens W, Aertsen A, Ceyssens PJ, Lavigne R. Antibacterial phage ORFans of Pseudomonas aeruginosa phage LUZ24 reveal a novel MvaT inhibiting protein. Front Microbiol 2015; 6:1242. [PMID: 26594207 PMCID: PMC4635203 DOI: 10.3389/fmicb.2015.01242] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 10/26/2015] [Indexed: 11/13/2022] Open
Abstract
The functional elucidation of small unknown phage proteins (‘ORFans’) presents itself as one of the major challenges of bacteriophage molecular biology. In this work, we mined the Pseudomonas aeruginosa-infecting phage LUZ24 proteome for antibacterial and antibiofilm proteins against its host. Subsequently, their putative host target was identified. In one example, we observed an interaction between LUZ24 gp4 and the host transcriptional regulator MvaT. The polymerization of MvaT across AT-rich DNA strands permits gene silencing of foreign DNA, thereby limiting any potentially adverse effects of such DNA. Gel shift assays proved the inhibitory effect of LUZ24 gp4 on MvaT DNA binding activity. Therefore, we termed this gene product as Mip, the MvaT inhibiting protein. We hypothesize Mip prevents the AT-rich LUZ24 DNA from being physically blocked by MvaT oligomers right after its injection in the host cell, thereby allowing phage transcription and thus completion of the phage infection cycle.
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Affiliation(s)
- Jeroen Wagemans
- Laboratory of Gene Technology, Department of Biosystems, KU Leuven Leuven, Belgium
| | - Anne-Sophie Delattre
- Laboratory of Gene Technology, Department of Biosystems, KU Leuven Leuven, Belgium
| | - Birgit Uytterhoeven
- Laboratory of Gene Technology, Department of Biosystems, KU Leuven Leuven, Belgium
| | - Jeroen De Smet
- Laboratory of Gene Technology, Department of Biosystems, KU Leuven Leuven, Belgium
| | - William Cenens
- Laboratory of Food Microbiology, Department of Microbial and Molecular Systems, KU Leuven Leuven, Belgium
| | - Abram Aertsen
- Laboratory of Food Microbiology, Department of Microbial and Molecular Systems, KU Leuven Leuven, Belgium
| | - Pieter-Jan Ceyssens
- Laboratory of Gene Technology, Department of Biosystems, KU Leuven Leuven, Belgium
| | - Rob Lavigne
- Laboratory of Gene Technology, Department of Biosystems, KU Leuven Leuven, Belgium
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9
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Ayala JC, Wang H, Silva AJ, Benitez JA. Repression by H-NS of genes required for the biosynthesis of the Vibrio cholerae biofilm matrix is modulated by the second messenger cyclic diguanylic acid. Mol Microbiol 2015; 97:630-45. [PMID: 25982817 DOI: 10.1111/mmi.13058] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Expression of Vibrio cholerae genes required for the biosynthesis of exopolysacchide (vps) and protein (rbm) components of the biofilm matrix is enhanced by cyclic diguanylate (c-di-GMP). In a previous study, we reported that the histone-like nucleoid structuring (H-NS) protein represses the transcription of vpsA, vpsL and vpsT. Here we demonstrate that the regulator VpsT can disrupt repressive H-NS nucleoprotein complexes at the vpsA and vpsL promoters in the presence of c-di-GMP, while H-NS could disrupt the VpsT-promoter complexes in the absence of c-di-GMP. Chromatin immunoprecipitation-Seq showed a remarkable trend for H-NS to cluster at loci involved in biofilm development such as the rbmABCDEF genes. We show that the antagonistic relationship between VpsT and H-NS regulates the expression of the rbmABCDEF cluster. Epistasis analysis demonstrated that VpsT functions as an antirepressor at the rbmA/F, vpsU and vpsA/L promoters. Deletion of vpsT increased H-NS occupancy at these promoters while increasing the c-di-GMP pool had the opposite effect and included the vpsT promoter. The negative effect of c-di-GMP on H-NS occupancy at the vpsT promoter required the regulator VpsR. These results demonstrate that c-di-GMP activates the transcription of genes required for the biosynthesis of the biofilm matrix by triggering a coordinated VpsR- and VpsT-dependent H-NS antirepression cascade.
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Affiliation(s)
- Julio C Ayala
- University of Alabama at Birmingham, Department of Microbiology, Birmingham, Alabama.,Morehouse School of Medicine, Department of Microbiology, Biochemistry and Immunology, Atlanta, Georgia
| | - Hongxia Wang
- Morehouse School of Medicine, Department of Microbiology, Biochemistry and Immunology, Atlanta, Georgia.,State Key Laboratory for Infectious Disease Prevention and Control and National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Changping, Beijing, China
| | - Anisia J Silva
- Morehouse School of Medicine, Department of Microbiology, Biochemistry and Immunology, Atlanta, Georgia
| | - Jorge A Benitez
- Morehouse School of Medicine, Department of Microbiology, Biochemistry and Immunology, Atlanta, Georgia
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10
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Dorman CJ. Integrating small molecule signalling and H-NS antagonism in Vibrio cholerae, a bacterium with two chromosomes. Mol Microbiol 2015; 97:612-5. [PMID: 25988304 DOI: 10.1111/mmi.13063] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/14/2015] [Indexed: 12/13/2022]
Abstract
H-NS is a well-established silencer of virulence gene transcription in the human pathogen Vibrio cholerae. Biofilm formation aids V. cholerae in colonizing both its host and its external environments, and H-NS silences biofilm gene expression. Cyclic-di-guanosine monophosphate acts through the DNA binding proteins VpsR and VpsT to overcome H-NS-mediated repression of biofilm genes, driving a transition between a planktonic and a colonial/biofilm lifestyle. The H-NS binding pattern has now been charted on both chromosomes in V. cholerae, but whether or not this abundant DNA-binding-and-bridging protein plays any roles in nucleoid organization in this bacterium remains an open question.
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Affiliation(s)
- Charles J Dorman
- Department of Microbiology, Moyne Institute of Preventive Medicine, School of Genetics and Microbiology, Trinity College Dublin, Dublin 2, Ireland
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11
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Wang H, Ayala JC, Benitez JA, Silva AJ. RNA-seq analysis identifies new genes regulated by the histone-like nucleoid structuring protein (H-NS) affecting Vibrio cholerae virulence, stress response and chemotaxis. PLoS One 2015; 10:e0118295. [PMID: 25679988 PMCID: PMC4332508 DOI: 10.1371/journal.pone.0118295] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Accepted: 01/13/2015] [Indexed: 12/20/2022] Open
Abstract
The histone-like nucleoid structuring protein (H-NS) functions as a transcriptional silencer by binding to AT-rich sequences at bacterial promoters. However, H-NS repression can be counteracted by other transcription factors in response to environmental changes. The identification of potential toxic factors, the expression of which is prevented by H-NS could facilitate the discovery of new regulatory proteins that may contribute to the emergence of new pathogenic variants by anti-silencing. Vibrio cholerae hns mutants of the El Tor biotype exhibit altered virulence, motility and environmental stress response phenotypes compared to wild type. We used an RNA-seq analysis approach to determine the basis of the above hns phenotypes and identify new targets of H-NS transcriptional silencing. H-NS affected the expression of 18% of all predicted genes in a growth phase-dependent manner. Loss of H-NS resulted in diminished expression of numerous genes encoding methyl-accepting chemotaxis proteins as well as chemotaxis toward the attractants glycine and serine. Deletion of hns also induced an endogenous envelope stress response resulting in elevated expression of rpoE encoding the extracytoplamic sigma factor E (σE). The RNA-seq analysis identified new genes directly repressed by H-NS that can affect virulence and biofilm development in the El Tor biotype cholera bacterium. We show that H-NS and the quorum sensing regulator HapR silence the transcription of the vieSAB three-component regulatory system in El Tor biotype V. cholerae. We also demonstrate that H-NS directly represses the transcription of hlyA (hemolysin), rtxCA (the repeat in toxin or RTX), rtxBDE (RTX transport) and the biosynthesis of indole. Of these genes, H-NS occupancy at the hlyA promoter was diminished by overexpression of the transcription activator HlyU. We discuss the role of H-NS transcriptional silencing in phenotypic differences exhibited by V. cholerae biotypes.
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Affiliation(s)
- Hongxia Wang
- Morehouse School of Medicine Department of Microbiology, Biochemistry and Immunology, Atlanta, Georgia, United States of America
- State Key Laboratory for Infectious Disease Prevention and Control, and National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Changping, Beijing, China
| | - Julio C. Ayala
- University of Alabama at Birmingham Department of Microbiology, Birmingham, Alabama, United States of America
| | - Jorge A. Benitez
- Morehouse School of Medicine Department of Microbiology, Biochemistry and Immunology, Atlanta, Georgia, United States of America
| | - Anisia J. Silva
- Morehouse School of Medicine Department of Microbiology, Biochemistry and Immunology, Atlanta, Georgia, United States of America
- * E-mail:
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12
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Haas BL, Matson JS, DiRita VJ, Biteen JS. Single-molecule tracking in live Vibrio cholerae reveals that ToxR recruits the membrane-bound virulence regulator TcpP to the toxT promoter. Mol Microbiol 2014; 96:4-13. [PMID: 25318589 DOI: 10.1111/mmi.12834] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/14/2014] [Indexed: 11/26/2022]
Abstract
Vibrio cholerae causes the human disease cholera by producing a potent toxin. The V. cholerae virulence pathway involves an unusual transcription step: the bitopic inner-membrane proteins TcpP and ToxR activate toxT transcription. As ToxT is the primary direct transcription activator in V. cholerae pathogenicity, its regulation by membrane-localized activators is key in the disease process. However, the molecular mechanisms by which membrane-localized activators engage the transcription process have yet to be uncovered in live cells. Here we report the use of super-resolution microscopy, single-molecule tracking, and gene knockouts to examine the dynamics of individual TcpP proteins in live V. cholerae cells with < 40 nm spatial resolution on a 50 ms timescale. Single-molecule trajectory analysis reveals that TcpP diffusion is heterogeneous and can be described by three populations of TcpP motion: one fast, one slow, and one immobile. By comparing TcpP diffusion in wild-type V. cholerae to that in mutant strains lacking either toxR or the toxT promoter, we determine that TcpP mobility is greater in the presence of its interaction partners than in their absence. Our findings support a mechanism in which ToxR recruits TcpP to the toxT promoter for transcription activation.
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Affiliation(s)
- Beth L Haas
- Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA
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13
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Abstract
Vibrio cholerae is an aquatic organism that causes the severe acute diarrheal disease cholera. The ability of V. cholerae to cause disease is dependent upon the production of two critical virulence determinants, cholera toxin (CT) and the toxin-coregulated pilus (TCP). The expression of the genes that encode for CT and TCP production is under the control of a hierarchical regulatory system called the ToxR regulon, which functions to activate virulence gene expression in response to in vivo stimuli. Cyclic dipeptides have been found to be produced by numerous bacteria, yet their biological function remains unknown. V. cholerae has been shown to produce cyclo(Phe-Pro). Previous studies in our laboratory demonstrated that cyclo(Phe-Pro) inhibited V. cholerae virulence factor production. For this study, we report on the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We have demonstrated that exogenous cyclo(Phe-Pro) activated the expression of leuO, a LysR-family regulator that had not been previously associated with V. cholerae virulence. Increased leuO expression repressed aphA transcription, which resulted in downregulation of the ToxR regulon and attenuated CT and TCP production. The cyclo(Phe-Pro)-dependent induction of leuO expression was found to be dependent upon the virulence regulator ToxR. Cyclo(Phe-Pro) did not affect toxR transcription or ToxR protein levels but appeared to enhance the ToxR-dependent transcription of leuO. These results have identified leuO as a new component of the ToxR regulon and demonstrate for the first time that ToxR is capable of downregulating virulence gene expression in response to an environmental cue. The ToxR regulon has been a focus of cholera research for more than three decades. During this time, a model has emerged wherein ToxR functions to activate the expression of Vibrio cholerae virulence factors upon host entry. V. cholerae and other enteric bacteria produce cyclo(Phe-Pro), a cyclic dipeptide that we identified as an inhibitor of V. cholerae virulence factor production. This finding suggested that cyclo(Phe-Pro) was a negative effector of virulence factor production and represented a molecule that could potentially be exploited for therapeutic development. In this work, we investigated the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We found that cyclo(Phe-Pro) signaled through ToxR to activate the expression of leuO, a new virulence regulator that functioned to repress virulence factor production. Our results have identified a new arm of the ToxR regulon and suggest that ToxR may play a broader role in pathogenesis than previously known.
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14
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Interaction of the histone-like nucleoid structuring protein and the general stress response regulator RpoS at Vibrio cholerae promoters that regulate motility and hemagglutinin/protease expression. J Bacteriol 2011; 194:1205-15. [PMID: 22194453 DOI: 10.1128/jb.05900-11] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The bacterium Vibrio cholerae colonizes the human small intestine and secretes cholera toxin (CT) to cause the rice-watery diarrhea characteristic of this illness. The ability of this pathogen to colonize the small bowel, express CT, and return to the aquatic environment is controlled by a complex network of regulatory proteins. Two global regulators that participate in this process are the histone-like nucleoid structuring protein (H-NS) and the general stress response regulator RpoS. In this study, we address the role of RpoS and H-NS in the coordinate regulation of motility and hemagglutinin (HA)/protease expression. In addition to initiating transcription of hapA encoding HA/protease, RpoS enhanced flrA and rpoN transcription to increase motility. In contrast, H-NS was found to bind to the flrA, rpoN, and hapA promoters and represses their expression. The strength of H-NS repression at the above-mentioned promoters was weaker for hapA, which exhibited the strongest RpoS dependency, suggesting that transcription initiation by RNA polymerase containing σ(S) could be more resistant to H-NS repression. Occupancy of the flrA and hapA promoters by H-NS was demonstrated by chromatin immunoprecipitation (ChIP). We show that the expression of RpoS in the stationary phase significantly diminished H-NS promoter occupancy. Furthermore, RpoS enhanced the transcription of integration host factor (IHF), which positively affected the expression of flrA and rpoN by diminishing the occupancy of H-NS at these promoters. Altogether, we propose a model for RpoS regulation of motility gene expression that involves (i) attenuation of H-NS repression by IHF and (ii) RpoS-dependent transcription initiation resistant to H-NS.
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15
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The 5.5 protein of phage T7 inhibits H-NS through interactions with the central oligomerization domain. J Bacteriol 2011; 193:4881-92. [PMID: 21764926 DOI: 10.1128/jb.05198-11] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The 5.5 protein (T7p32) of coliphage T7 (5.5(T7)) was shown to bind and inhibit gene silencing by the nucleoid-associated protein H-NS, but the mechanism by which it acts was not understood. The 5.5(T7) protein is insoluble when expressed in Escherichia coli, but we find that 5.5(T7) can be isolated in a soluble form when coexpressed with a truncated version of H-NS followed by subsequent disruption of the complex during anion-exchange chromatography. Association studies reveal that 5.5(T7) binds a region of H-NS (residues 60 to 80) recently found to contain a distinct domain necessary for higher-order H-NS oligomerization. Accordingly, we find that purified 5.5(T7) can disrupt higher-order H-NS-DNA complexes in vitro but does not abolish DNA binding by H-NS per se. Homologues of the 5.5(T7) protein are found exclusively among members of the Autographivirinae that infect enteric bacteria, and despite fairly low sequence conservation, the H-NS binding properties of these proteins are largely conserved. Unexpectedly, we find that the 5.5(T7) protein copurifies with heterogeneous low-molecular-weight RNA, likely tRNA, through several chromatography steps and that this interaction does not require the DNA binding domain of H-NS. The 5.5 proteins utilize a previously undescribed mechanism of H-NS antagonism that further highlights the critical importance that higher-order oligomerization plays in H-NS-mediated gene repression.
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Abstract
Expression of the ctx and tcp genes, which encode cholera toxin and the toxin coregulated pilus, the Vibrio cholerae O1 virulence determinants having the largest contribution to cholera disease, is repressed by the nucleoid-associated protein H-NS and activated by the AraC-like transcriptional regulator ToxT. To elucidate the molecular mechanism by which H-NS controls transcription of the ctxAB operon, H-NS repression and binding were characterized by using a promoter truncation series, gel mobility shift assays, and DNase I footprinting. Promoter regions found to be important for H-NS repression correlated with in vitro binding. Four main H-NS binding regions are present at ctx. One region overlaps the high-affinity ToxT binding site and extends upstream, another overlaps the ToxT low-affinity binding site around the -35 element, and the remaining two are located adjacent to one another downstream of the transcriptional start site. Competition for binding to the overlapping H-NS/ToxT binding sites was observed in gel mobility shift assays, where ToxT was found to displace H-NS from the ctx promoter region. In addition, regulatory differences between the ctx and tcpA promoters were examined. H-NS was found to have a higher relative binding affinity for the ctx promoter than for the tcpA promoter in vitro. In contrast to ToxT-dependent activation of the tcpA promoter, ToxT activation of ctx did not require the C-terminal domain of the α-subunit of RNA polymerase. These findings demonstrate that transcriptional regulation of ctx and tcpA by H-NS and ToxT is mechanistically distinct, and this may lead to important differences in the expression of these coregulated genes.
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Abstract
Emerging models of the bacterial nucleoid show that nucleoid-associated proteins (NAPs) and transcription contribute in combination to the dynamic nature of nucleoid structure. NAPs and other DNA-binding proteins that display gene-silencing and anti-silencing activities are emerging as key antagonistic regulators of nucleoid structure. Furthermore, it is becoming clear that the boundary between NAPs and conventional transcriptional regulators is quite blurred and that NAPs facilitate the evolution of novel gene regulatory circuits. Here, NAP biology is considered from the standpoints of both gene regulation and nucleoid structure.
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N9L and L9N mutations toggle Hha binding and hemolysin regulation byEscherichia coliandVibrio choleraeH-NS. FEBS Lett 2009; 583:2911-6. [DOI: 10.1016/j.febslet.2009.07.054] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2009] [Revised: 07/28/2009] [Accepted: 07/29/2009] [Indexed: 11/18/2022]
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Role of the histone-like nucleoid structuring protein in the regulation of rpoS and RpoS-dependent genes in Vibrio cholerae. J Bacteriol 2008; 190:7335-45. [PMID: 18790865 DOI: 10.1128/jb.00360-08] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Production of the Zn-metalloprotease hemagglutinin (HA)/protease by Vibrio cholerae has been reported to enhance enterotoxicity in rabbit ileal loops and the reactogenicity of live cholera vaccine candidates. Expression of HA/protease requires the alternate sigma factor sigma(S) (RpoS), encoded by rpoS. The histone-like nucleoid structuring protein (H-NS) has been shown to repress rpoS expression in Escherichia coli. In V. cholerae strains of the classical biotype, H-NS has been reported to silence virulence gene expression. In this study we examined the role of H-NS in the expression of HA/protease and motility in an El Tor biotype strain by constructing a Deltahns mutant. The Deltahns mutant exhibited multiple phenotypes, such as production of cholera toxin in nonpermissive LB medium, reduced resistance to high osmolarity, enhanced resistance to low pH and hydrogen peroxide, and reduced motility. Depletion of H-NS by overexpression of a dominant-negative allele or by deletion of hns resulted in diminished expression of HA/protease. Epistasis analysis of HA/protease expression in Deltahns, DeltarpoS, and Deltahns DeltarpoS mutants, analysis of RpoS reporter fusions, quantitative reverse transcription-PCR measurements, and ectopic expression of RpoS in DeltarpoS and DeltarpoS Deltahns mutants showed that H-NS posttranscriptionally enhances RpoS expression. The Deltahns mutant exhibited a lower degree of motility and lower levels of expression of flaA, flaC, cheR-2, and motX mRNAs than the wild type. Comparison of the mRNA abundances of these genes in wild-type, Deltahns, DeltarpoS, and Deltahns DeltarpoS strains revealed that deletion of rpoS had a more severe negative effect on their expression. Interestingly, deletion of hns in the rpoS background resulted in higher expression levels of flaA, flaC, and motX, suggesting that H-NS represses the expression of these genes in the absence of sigma(S). Finally, we show that the cyclic AMP receptor protein and H-NS act along the same pathway to positively affect RpoS expression.
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Abstract
Two recent reports have indicated that the H-NS protein in Salmonella enterica serovar Typhimurium has a key role in selectively silencing the transcription of large numbers of horizontally acquired AT-rich genes, including those that make up its major pathogenicity islands. Broadly similar conclusions have emerged from a study of H-NS binding to DNA in Escherichia coli. How do these findings affect our view of H-NS and its ability to influence bacterial evolution?
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Affiliation(s)
- Charles J Dorman
- Department of Microbiology, Trinity College Dublin, Dublin, Ireland.
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García J, Madrid C, Juárez A, Pons M. New roles for key residues in helices H1 and H2 of the Escherichia coli H-NS N-terminal domain: H-NS dimer stabilization and Hha binding. J Mol Biol 2006; 359:679-89. [PMID: 16650431 DOI: 10.1016/j.jmb.2006.03.059] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2006] [Revised: 03/07/2006] [Accepted: 03/29/2006] [Indexed: 10/24/2022]
Abstract
Bacterial nucleoid-associated proteins H-NS and Hha modulate gene expression in response to environmental factors. The N-terminal domain of H-NS is involved in homomeric and heteromeric protein-protein interactions. Homomeric interaction leads to the formation of dimers and higher oligomers. Heteromeric interactions with Hha-like proteins modify the modulatory properties of H-NS. In this study, we have used NMR and mutagenesis of the N-terminal domain of H-NS to identify the Hha-binding region around helices H1 and H2 of H-NS. Two conserved arginine residues, R12 and R15, located in the same side and in adjacent turns of helix H2 are shown to be involved in two different protein-protein interactions: R12 is essential for Hha binding and does not affect H-NS dimer formation, and R15 does not affect Hha binding but is essential for the proper folding of H-NS dimers. Our results demonstrate a close structural connection between Hha-H-NS interactions and H-NS dimerization that may be involved in a possible mechanism for the modulation of the H-NS regulatory activity by Hha.
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Affiliation(s)
- Jesús García
- Laboratory of Biomolecular NMR, Institut de Recerca Biomèdica-Parc Científic de Barcelona, Josep Samitier, 1-5 08028 Barcelona, Spain
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Ono S, Goldberg M, Olsson T, Esposito D, Hinton J, Ladbury J. H-NS is a part of a thermally controlled mechanism for bacterial gene regulation. Biochem J 2005; 391:203-13. [PMID: 15966862 PMCID: PMC1276917 DOI: 10.1042/bj20050453] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2005] [Revised: 06/20/2005] [Accepted: 06/21/2005] [Indexed: 01/03/2023]
Abstract
Temperature is a primary environmental stress to which micro-organisms must be able to adapt and respond rapidly. Whereas some bacteria are restricted to specific niches and have limited abilities to survive changes in their environment, others, such as members of the Enterobacteriaceae, can withstand wide fluctuations in temperature. In addition to regulating cellular physiology, pathogenic bacteria use temperature as a cue for activating virulence gene expression. This work confirms that the nucleoid-associated protein H-NS (histone-like nucleoid structuring protein) is an essential component in thermoregulation of Salmonella. On increasing the temperature from 25 to 37 degrees C, more than 200 genes from Salmonella enterica serovar Typhimurium showed H-NS-dependent up-regulation. The thermal activation of gene expression is extremely rapid and change in temperature affects the DNA-binding properties of H-NS. The reduction in gene repression brought about by the increase in temperature is concomitant with a conformational change in the protein, resulting in the decrease in size of high-order oligomers and the appearance of increasing concentrations of discrete dimers of H-NS. The present study addresses one of the key complex mechanisms by which H-NS regulates gene expression.
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Affiliation(s)
- Shusuke Ono
- *Department of Biochemistry and Molecular Biology, and Institute of Structural Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K
| | - Martin D. Goldberg
- †Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, U.K
| | - Tjelvar Olsson
- *Department of Biochemistry and Molecular Biology, and Institute of Structural Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K
| | - Diego Esposito
- *Department of Biochemistry and Molecular Biology, and Institute of Structural Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K
| | - Jay C. D. Hinton
- †Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, U.K
| | - John E. Ladbury
- *Department of Biochemistry and Molecular Biology, and Institute of Structural Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K
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Rimsky S. Structure of the histone-like protein H-NS and its role in regulation and genome superstructure. Curr Opin Microbiol 2004; 7:109-14. [PMID: 15063845 DOI: 10.1016/j.mib.2004.02.001] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
H-NS belongs to the group of histone-like proteins in Gram-negative bacteria and is also a pleiotropic regulator of genes implicated in many responses to environmental changes. It plays a dual role in structuring DNA and in regulating transcription. Recent advances have been made in elucidating the structure and oligomerisation properties of this protein, thus aiding in the understanding of the molecular relationship between its two major functions.
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Affiliation(s)
- Sylvie Rimsky
- Enzymologie et Cinétique Structurale, LBPA, UMR 8113, Ecole Normale Supérieure de Cachan/CNRS/ Université Paris XI, 61 Avenue du Président Wilsons, 94235 Cachan cedex, France.
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Affiliation(s)
- Charles J Dorman
- Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, University of Dublin, Dublin 2, Ireland.
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