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CesL Regulates Type III Secretion Substrate Specificity of the Enteropathogenic E. coli Injectisome. Microorganisms 2021; 9:microorganisms9051047. [PMID: 34067942 PMCID: PMC8152094 DOI: 10.3390/microorganisms9051047] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 04/27/2021] [Accepted: 04/27/2021] [Indexed: 11/23/2022] Open
Abstract
The type III secretion system (T3SS) is a complex molecular device used by several pathogenic bacteria to translocate effector proteins directly into eukaryotic host cells. One remarkable feature of the T3SS is its ability to secrete different categories of proteins in a hierarchical manner, to ensure proper assembly and timely delivery of effectors into target cells. In enteropathogenic Escherichia coli, the substrate specificity switch from translocator to effector secretion is regulated by a gatekeeper complex composed of SepL, SepD, and CesL proteins. Here, we report a characterization of the CesL protein using biochemical and genetic approaches. We investigated discrepancies in the phenotype among different cesL deletion mutants and showed that CesL is indeed essential for translocator secretion and to prevent premature effector secretion. We also demonstrated that CesL engages in pairwise interactions with both SepL and SepD. Furthermore, while association of SepL to the membrane does not depended on CesL, the absence of any of the proteins forming the heterotrimeric complex compromised the intracellular stability of each component. In addition, we found that CesL interacts with the cytoplasmic domains of the export gate components EscU and EscV. We propose a mechanism for substrate secretion regulation governed by the SepL/SepD/CesL complex.
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Slater SL, Frankel G. Advances and Challenges in Studying Type III Secretion Effectors of Attaching and Effacing Pathogens. Front Cell Infect Microbiol 2020; 10:337. [PMID: 32733819 PMCID: PMC7358347 DOI: 10.3389/fcimb.2020.00337] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 06/04/2020] [Indexed: 12/24/2022] Open
Affiliation(s)
- Sabrina L Slater
- MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Gad Frankel
- MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London, United Kingdom
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Obradovic M, Pasternak JA, Hon Ng S, Allan B, Brownlie R, Wilson HL. Immunoproteomic analysis of Lawsonia intracellularis identifies candidate neutralizing antibody targets for use in subunit vaccine development. Vet Microbiol 2019; 235:270-279. [PMID: 31383312 DOI: 10.1016/j.vetmic.2019.07.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2019] [Revised: 06/28/2019] [Accepted: 07/18/2019] [Indexed: 12/17/2022]
Abstract
Lawsonia intracellularis is an obligate intracellular microorganism and the causative agent of porcine proliferative enteropathy. Due to its obligate intracellular nature, characterization of antigens and proteins involved in host-pathogen interaction and immune recognition have been difficult to achieve using conventional microbiological techniques. In this work, we used 2-dimensional gel electrophoresis coupled with Western-immunoblotting, mass spectrometry and bioinformatics to identify bacterial proteins that interact in vitro with pig intestinal cells (IPEC-1), have immunogenic properties and the potential to be used as subunit vaccine antigens. We detected eleven immunogenic bacterial proteins from which fliC (LI0710), LI1153 (annotated by NCBI as Putative protein N), and LI0649 (annotated as autotransporter) were predicted to be expressed on the outer membrane while LI0169 (oppA; annotated as ABC dipeptide transport system) was predicted to be periplasmic with a transmembrane domain forming a central pore through the plasma membrane. Genes coding for these four proteins were cloned and expressed in Escherichia coli and the corresponding recombinant proteins were purified using affinity chromatography. Porcine hyperimmune serum against whole Lawsonia lysate established that all four recombinant proteins were immunogenic. Further, rabbit hyperimmune sera generated against the vaccine strain of L. intracellularis and rabbit serum specific for each recombinant protein showed an inhibitory effect on the attachment and penetration of live, avirulent L. intracellularis, thus indicating that each protein is a potential neutralizing antibody target and a candidate for subunit vaccine formulation.
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Affiliation(s)
- Milan Obradovic
- Vaccine and Infectious Disease Organization (VIDO)-International Vaccine Centre (InterVac), University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E3, Canada; School of Public Health, Vaccinology and Immunotherapeutics, Saskatchewan, Canada
| | - J Alex Pasternak
- Large Animal Clinical Sciences (LACS), Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5B4, Canada
| | - Siew Hon Ng
- Vaccine and Infectious Disease Organization (VIDO)-International Vaccine Centre (InterVac), University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E3, Canada
| | - Brenda Allan
- Vaccine and Infectious Disease Organization (VIDO)-International Vaccine Centre (InterVac), University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E3, Canada
| | - Robert Brownlie
- Vaccine and Infectious Disease Organization (VIDO)-International Vaccine Centre (InterVac), University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E3, Canada
| | - Heather L Wilson
- Vaccine and Infectious Disease Organization (VIDO)-International Vaccine Centre (InterVac), University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E3, Canada; School of Public Health, Vaccinology and Immunotherapeutics, Saskatchewan, Canada.
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Bamyaci S, Nordfelth R, Forsberg Å. Identification of specific sequence motif of YopN of Yersinia pseudotuberculosis required for systemic infection. Virulence 2018; 10:10-25. [PMID: 30488778 PMCID: PMC6298760 DOI: 10.1080/21505594.2018.1551709] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Type III secretion systems (T3SSs) are tightly regulated key virulence mechanisms shared by many Gram-negative pathogens. YopN, one of the substrates, is also crucial in regulation of expression, secretion and activation of the T3SS of pathogenic Yersinia species. Interestingly, YopN itself is also targeted into host cells but so far no activity or direct role for YopN inside host cells has been described. Recently, we were able show that the central region of YopN is required for efficient translocation of YopH and YopE into host cells. This was also shown to impact the ability of Yersinia to block phagocytosis. One difficulty in studying YopN is to generate mutants that are not impaired in regulation of the T3SS. In this study we extended our previous work and were able to generate specific mutants within the central region of YopN. These mutants were predicted to be crucial for formation of a putative coiled-coil domain (CCD). Similar to the previously described deletion mutant of the central region, these mutants were all impaired in translocation of YopE and YopH. Interestingly, these YopN variants were not translocated into host cells. Importantly, when these mutants were introduced in cis on the virulence plasmid, they retained full regulatory function of T3SS expression and secretion. This allowed us to evaluate one of the mutants, yopNGAGA, in the systemic mouse infection model. Using in vivo imaging technology we could verify that the mutant was also attenuated in vivo and highly impaired to establish systemic infection.
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Affiliation(s)
- Sarp Bamyaci
- a Department of Molecular Biology, Umeå Centre for Microbial Research UCMR , Umeå University , Umeå , Sweden.,b Department of Molecular Biology, Laboratory for Molecular Infection Medicine MIMS , Umeå University , Umeå , Sweden
| | - Roland Nordfelth
- a Department of Molecular Biology, Umeå Centre for Microbial Research UCMR , Umeå University , Umeå , Sweden.,b Department of Molecular Biology, Laboratory for Molecular Infection Medicine MIMS , Umeå University , Umeå , Sweden
| | - Åke Forsberg
- a Department of Molecular Biology, Umeå Centre for Microbial Research UCMR , Umeå University , Umeå , Sweden.,b Department of Molecular Biology, Laboratory for Molecular Infection Medicine MIMS , Umeå University , Umeå , Sweden
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After the Fact(or): Posttranscriptional Gene Regulation in Enterohemorrhagic Escherichia coli O157:H7. J Bacteriol 2018; 200:JB.00228-18. [PMID: 29967119 DOI: 10.1128/jb.00228-18] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To adapt to ever-changing environments, pathogens quickly alter gene expression. This can occur through transcriptional, posttranscriptional, or posttranslational regulation. Historically, transcriptional regulation has been thoroughly studied to understand pathogen niche adaptation, whereas posttranscriptional and posttranslational gene regulation has only relatively recently been appreciated to play a central role in bacterial pathogenesis. Posttranscriptional regulation may involve chaperones, nucleases, and/or noncoding small RNAs (sRNAs) and typically controls gene expression by altering the stability and/or translation of the target mRNA. In this review, we highlight the global importance of posttranscriptional regulation to enterohemorrhagic Escherichia coli (EHEC) gene expression and discuss specific mechanisms of how EHEC regulates expression of virulence factors critical to host colonization and disease progression. The low infectious dose of this intestinal pathogen suggests that EHEC is particularly well adapted to respond to the host environment.
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Vibrio parahaemolyticus Senses Intracellular K + To Translocate Type III Secretion System 2 Effectors Effectively. mBio 2018; 9:mBio.01366-18. [PMID: 30042203 PMCID: PMC6058294 DOI: 10.1128/mbio.01366-18] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Many Gram-negative bacterial symbionts and pathogens employ a type III secretion system (T3SS) to live in contact with eukaryotic cells. Because T3SSs inject bacterial proteins (effectors) directly into host cells, the switching of secretory substrates between translocators and effectors in response to host cell attachment is a crucial step for the effective delivery of effectors. Here, we show that the protein secretion switch of Vibrio parahaemolyticus T3SS2, which is a main contributor to the enteropathogenicity of a food poisoning bacterium, is regulated by two gatekeeper proteins, VgpA and VgpB. In the absence of these gatekeepers, effector secretion was activated, but translocator secretion was abolished, causing the loss of virulence. We found that the K+ concentration, which is high inside the host cell but low outside, is a key factor for VgpA- and VgpB-mediated secretion switching. Exposure of wild-type bacteria to K+ ions provoked both gatekeeper and effector secretions but reduced the level of secretion of translocators. The secretion protein profile of wild-type bacteria cultured with 0.1 M KCl was similar to that of gatekeeper mutants. Furthermore, depletion of K+ ions in host cells diminished the efficiency of T3SS2 effector translocation. Thus, T3SS2 senses the high intracellular concentration of K+ of the host cell so that T3SS2 effectors can be effectively injected. The pathogenesis of many Gram-negative bacterial pathogens arises from a type III secretion system (T3SS), whereby bacterial proteins (effectors) are directly injected into host cells. The injected effectors then modify host cell functions. For effective delivery of effector proteins, bacteria need to both recognize host cell attachment and switch the type of secreted proteins. Here, we identified gatekeeper proteins that play important roles in a T3SS2 secretion switch of Vibrio parahaemolyticus, a causative agent of food-borne gastroenteritis. We also found that K+, which is present in high concentrations inside the host cell but in low concentrations outside, is a key factor for the secretion switch. Thus, V. parahaemolyticus senses the high intracellular K+ concentration, triggering the effective injection of effectors.
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Wang D, McAteer SP, Wawszczyk AB, Russell CD, Tahoun A, Elmi A, Cockroft SL, Tollervey D, Granneman S, Tree JJ, Gally DL. An RNA-dependent mechanism for transient expression of bacterial translocation filaments. Nucleic Acids Res 2018; 46:3366-3381. [PMID: 29432565 PMCID: PMC5909449 DOI: 10.1093/nar/gky096] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 01/28/2018] [Accepted: 02/06/2018] [Indexed: 12/31/2022] Open
Abstract
The prokaryotic RNA chaperone Hfq mediates sRNA-mRNA interactions and plays a significant role in post-transcriptional regulation of the type III secretion (T3S) system produced by a range of Escherichia coli pathotypes. UV-crosslinking was used to map Hfq-binding under conditions that promote T3S and multiple interactions were identified within polycistronic transcripts produced from the locus of enterocyte effacement (LEE) that encodes the T3S system. The majority of Hfq binding was within the LEE5 and LEE4 operons, the latter encoding the translocon apparatus (SepL-EspADB) that is positively regulated by the RNA binding protein, CsrA. Using the identified Hfq-binding sites and a series of sRNA deletions, the sRNA Spot42 was shown to directly repress translation of LEE4 at the sepL 5' UTR. In silico and in vivo analyses of the sepL mRNA secondary structure combined with expression studies of truncates indicated that the unbound sepL mRNA is translationally inactive. Based on expression studies with site-directed mutants, an OFF-ON-OFF toggle model is proposed that results in transient translation of SepL and EspA filament assembly. Under this model, the nascent mRNA is translationally off, before being activated by CsrA, and then repressed by Hfq and Spot42.
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Affiliation(s)
- Dai Wang
- Division of Infection and Immunity, The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh EH25 9RG, UK
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, School of Public Health, Xiamen University, South Xiangan Rd., Xiangan District, Xiamen, Fujian Province 361102, China
| | - Sean P McAteer
- Division of Infection and Immunity, The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh EH25 9RG, UK
| | - Agata B Wawszczyk
- Division of Infection and Immunity, The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh EH25 9RG, UK
- Centre for Synthetic and Systems Biology, University of Edinburgh, Edinburgh EH9 3BF, UK
| | - Clark D Russell
- Division of Infection and Immunity, The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh EH25 9RG, UK
| | - Amin Tahoun
- Division of Infection and Immunity, The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh EH25 9RG, UK
- Faculty of Veterinary Medicine, Kafrelsheikh University, 33516 Kafrel-Sheikh, Egypt
| | - Alex Elmi
- EaStCHEM School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, UK
| | - Scott L Cockroft
- EaStCHEM School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, UK
| | - David Tollervey
- Wellcome Centre for Cell Biology, University of Edinburgh, Edinburgh EH9 3BF, UK
| | - Sander Granneman
- Centre for Synthetic and Systems Biology, University of Edinburgh, Edinburgh EH9 3BF, UK
| | - Jai J Tree
- Division of Infection and Immunity, The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh EH25 9RG, UK
- Wellcome Centre for Cell Biology, University of Edinburgh, Edinburgh EH9 3BF, UK
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney 2052, NSW, Australia
| | - David L Gally
- Division of Infection and Immunity, The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh EH25 9RG, UK
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The QseG Lipoprotein Impacts the Virulence of Enterohemorrhagic Escherichia coli and Citrobacter rodentium and Regulates Flagellar Phase Variation in Salmonella enterica Serovar Typhimurium. Infect Immun 2018; 86:IAI.00936-17. [PMID: 29358334 DOI: 10.1128/iai.00936-17] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Accepted: 01/12/2018] [Indexed: 11/20/2022] Open
Abstract
The QseEF histidine kinase/response regulator system modulates expression of enterohemorrhagic Escherichia coli (EHEC) and Salmonella enterica serovar Typhimurium virulence genes in response to the host neurotransmitters epinephrine and norepinephrine. qseG, which encodes an outer membrane lipoprotein, is cotranscribed with qseEF in these enteric pathogens, but there is little knowledge of its role in virulence. Here, we found that in EHEC QseG interacts with the type III secretion system (T3SS) gate protein SepL and modulates the kinetics of attaching and effacing (AE) lesion formation on tissue-cultured cells. Moreover, an EHEC ΔqseG mutant had reduced intestinal colonization in an infant rabbit model. Additionally, in Citrobacter rodentium, an AE lesion-forming pathogen like EHEC, QseG is required for full virulence in a mouse model. In S Typhimurium, we found that QseG regulates the phase switch between the two flagellin types, FliC and FljB. In an S Typhimurium ΔqseG mutant, the phase-variable promoter for fljB is preferentially switched into the "on" position, leading to overproduction of this phase two flagellin. In infection of tissue-cultured cells, the S Typhimurium ΔqseG mutant provokes increased inflammatory cytokine production versus the wild type; in vivo, in a murine infection model, the ΔqseG strain caused a more severe inflammatory response and was attenuated versus the wild-type strain. Collectively, our findings demonstrate that QseG is important for full virulence in several enteric pathogens and controls flagellar phase variation in S Typhimurium, and they highlight both the complexity and conservation of the regulatory networks that control the virulence of enteric pathogens.
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Vander Broek CW, Stevens JM. Type III Secretion in the Melioidosis Pathogen Burkholderia pseudomallei. Front Cell Infect Microbiol 2017; 7:255. [PMID: 28664152 PMCID: PMC5471309 DOI: 10.3389/fcimb.2017.00255] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Accepted: 05/31/2017] [Indexed: 02/03/2023] Open
Abstract
Burkholderia pseudomallei is a Gram-negative intracellular pathogen and the causative agent of melioidosis, a severe disease of both humans and animals. Melioidosis is an emerging disease which is predicted to be vastly under-reported. Type III Secretion Systems (T3SSs) are critical virulence factors in Gram negative pathogens of plants and animals. The genome of B. pseudomallei encodes three T3SSs. T3SS-1 and -2, of which little is known, are homologous to Hrp2 secretion systems of the plant pathogens Ralstonia and Xanthomonas. T3SS-3 is better characterized and is homologous to the Inv/Mxi-Spa secretion systems of Salmonella spp. and Shigella flexneri, respectively. Upon entry into the host cell, B. pseudomallei requires T3SS-3 for efficient escape from the endosome. T3SS-3 is also required for full virulence in both hamster and murine models of infection. The regulatory cascade which controls T3SS-3 expression and the secretome of T3SS-3 have been described, as well as the effect of mutations of some of the structural proteins. Yet only a few effector proteins have been functionally characterized to date and very little work has been carried out to understand the hierarchy of assembly, secretion and temporal regulation of T3SS-3. This review aims to frame current knowledge of B. pseudomallei T3SSs in the context of other well characterized model T3SSs, particularly those of Salmonella and Shigella.
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Affiliation(s)
- Charles W Vander Broek
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of EdinburghMidlothian, United Kingdom
| | - Joanne M Stevens
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of EdinburghMidlothian, United Kingdom
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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: 117] [Impact Index Per Article: 14.6] [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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Vander Broek CW, Chalmers KJ, Stevens MP, Stevens JM. Quantitative proteomic analysis of Burkholderia pseudomallei Bsa type III secretion system effectors using hypersecreting mutants. Mol Cell Proteomics 2015; 14:905-16. [PMID: 25635268 PMCID: PMC4390269 DOI: 10.1074/mcp.m114.044875] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Revised: 01/07/2015] [Indexed: 11/06/2022] Open
Abstract
Burkholderia pseudomallei is an intracellular pathogen and the causative agent of melioidosis, a severe disease of humans and animals. One of the virulence factors critical for early stages of infection is the Burkholderia secretion apparatus (Bsa) Type 3 Secretion System (T3SS), a molecular syringe that injects bacterial proteins, called effectors, into eukaryotic cells where they subvert cellular functions to the benefit of the bacteria. Although the Bsa T3SS itself is known to be important for invasion, intracellular replication, and virulence, only a few genuine effector proteins have been identified and the complete repertoire of proteins secreted by the system has not yet been fully characterized. We constructed a mutant lacking bsaP, a homolog of the T3SS "gatekeeper" family of proteins that exert control over the timing and magnitude of effector protein secretion. Mutants lacking BsaP, or the T3SS translocon protein BipD, were observed to hypersecrete the known Bsa effector protein BopE, providing evidence of their role in post-translational control of the Bsa T3SS and representing key reagents for the identification of its secreted substrates. Isobaric Tags for Relative and Absolute Quantification (iTRAQ), a gel-free quantitative proteomics technique, was used to compare the secreted protein profiles of the Bsa T3SS hypersecreting mutants of B. pseudomallei with the isogenic parent strain and a bsaZ mutant incapable of effector protein secretion. Our study provides one of the most comprehensive core secretomes of B. pseudomallei described to date and identified 26 putative Bsa-dependent secreted proteins that may be considered candidate effectors. Two of these proteins, BprD and BapA, were validated as novel effector proteins secreted by the Bsa T3SS of B. pseudomallei.
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Affiliation(s)
- Charles W Vander Broek
- From the ‡The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian, EH25 9RG, Scotland, UK
| | - Kevin J Chalmers
- §Dundee Cell Products, James Lindsay Place, Dundee Technopole, Dundee, DD1 5JJ, Scotland, UK
| | - Mark P Stevens
- From the ‡The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian, EH25 9RG, Scotland, UK
| | - Joanne M Stevens
- From the ‡The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian, EH25 9RG, Scotland, UK.;
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SepD/SepL-dependent secretion signals of the type III secretion system translocator proteins in enteropathogenic Escherichia coli. J Bacteriol 2015; 197:1263-75. [PMID: 25645555 DOI: 10.1128/jb.02401-14] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The type III protein secretion system (T3SS) encoded by the locus of enterocyte effacement (LEE) is essential for the pathogenesis of attaching/effacing bacterial pathogens, including enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and Citrobacter rodentium. These pathogens use the T3SS to sequentially secrete three categories of proteins: the T3SS needle and inner rod protein components; the EspA, EspB, and EspD translocators; and many LEE- and non-LEE-encoded effectors. SepD and SepL are essential for translocator secretion, and mutations in either lead to hypersecretion of effectors. However, how SepD and SepL control translocator secretion and secretion hierarchy between translocators and effectors is poorly understood. In this report, we show that the secreted T3SS components, the translocators, and both LEE- and non-LEE-encoded effectors all carry N-terminal type III secretion and translocation signals. These signals all behave like those of the effectors and are sufficient for mediating type III secretion and translocation by wild-type EPEC and hypersecretion by the sepD and sepL mutants. Our results extended previous observations and suggest that the secretion hierarchy of the different substrates is determined by a signal other than the N-terminal secretion signal. We identified a domain located immediately downstream of the N-terminal secretion signal in the translocator EspB that is required for SepD/SepL-dependent secretion. We further demonstrated that this EspB domain confers SepD/SepL- and CesAB-dependent secretion on the secretion signal of effector EspZ. Our results thus suggest that SepD and SepL control and regulate secretion hierarchy between translocators and effectors by recognizing translocator-specific export signals. IMPORTANCE Many bacterial pathogens use a syringe-like protein secretion apparatus, termed the type III protein secretion system (T3SS), to secrete and inject numerous proteins directly into the host cells to cause disease. The secreted proteins perform different functions at various stages during infection and are classified into three substrate categories (T3SS components, translocators, and effectors). They all contain secretion signals at their N termini, but how their secretion hierarchy is determined is poorly understood. Here, we show that the N-terminal secretion signals from different substrate categories all behave the same and do not confer substrate specificity. We further characterize the secretion signals of the translocators and identify a translocator-specific signal, demonstrating that substrate-specific secretion signals are required in regulating T3SS substrate hierarchy.
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Burkinshaw BJ, Strynadka NCJ. Assembly and structure of the T3SS. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1649-63. [PMID: 24512838 DOI: 10.1016/j.bbamcr.2014.01.035] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Revised: 01/27/2014] [Accepted: 01/29/2014] [Indexed: 02/06/2023]
Abstract
The Type III Secretion System (T3SS) is a multi-mega Dalton apparatus assembled from more than twenty components and is found in many species of animal and plant bacterial pathogens. The T3SS creates a contiguous channel through the bacterial and host membranes, allowing injection of specialized bacterial effector proteins directly to the host cell. In this review, we discuss our current understanding of T3SS assembly and structure, as well as highlight structurally characterized Salmonella effectors. 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)
- Brianne J Burkinshaw
- Department of Biochemistry and Molecular Biology, Center for Blood Research, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
| | - Natalie C J Strynadka
- Department of Biochemistry and Molecular Biology, Center for Blood Research, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
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Reiland HA, Omolo MA, Johnson TJ, Baumler DJ. A Survey of <i>Escherichia coli</i> O157:H7 Virulence Factors: The First 25 Years and 13 Genomes. ACTA ACUST UNITED AC 2014. [DOI: 10.4236/aim.2014.47046] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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15
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Rahal EA, Kazzi N, Nassar FJ, Matar GM. Escherichia coli O157:H7-Clinical aspects and novel treatment approaches. Front Cell Infect Microbiol 2012; 2:138. [PMID: 23162800 PMCID: PMC3498739 DOI: 10.3389/fcimb.2012.00138] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Accepted: 10/19/2012] [Indexed: 12/25/2022] Open
Abstract
Escherichia coli O157:H7 is a notorious pathogen often contracted by intake of contaminated water or food. Infection with this agent is associated with a broad spectrum of illness ranging from mild diarrhea and hemorrhagic colitis to the potentially fatal hemolytic uremic syndrome (HUS). Treating E. coli O157:H7 infection with antimicrobial agents is associated with an increased risk of severe sequelae such as HUS. The difficulty in treating this bacterium using conventional modalities of antimicrobial agent administration has sparked an interest in investigating new therapeutic approaches to this bacterium. These approaches have included the use of probiotic agents and natural products with variable success rates. In addition, novel modalities and regimen of antimicrobial agent administration have been assessed in an attempt at decreasing their association with aggravating infection outcomes.
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Affiliation(s)
- Elias A Rahal
- Faculty of Medicine, Department of Experimental Pathology, Immunology and Microbiology, American University of Beirut Beirut, Lebanon
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16
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Lodato PB, Hsieh PK, Belasco JG, Kaper JB. The ribosome binding site of a mini-ORF protects a T3SS mRNA from degradation by RNase E. Mol Microbiol 2012; 86:1167-82. [PMID: 23043360 DOI: 10.1111/mmi.12050] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/19/2012] [Indexed: 11/28/2022]
Abstract
Enterohaemorrhagic Escherichia coli harbours a pathogenicity island encoding a type 3 secretion system used to translocate effector proteins into the cytosol of intestinal epithelial cells and subvert their function. The structural proteins of the translocon are encoded in a major espADB mRNA processed from a precursor. The translocon mRNA should be highly susceptible to RNase E cleavage because of its AU-rich leader region and monophosphorylated 5'-terminus, yet it manages to avoid rapid degradation. Here, we report that the espADB leader region contains a strong Shine-Dalgarno element (SD2) and a translatable mini-ORF of six codons. Disruption of SD2 so as to weaken ribosome binding significantly reduces the concentration and stability of esp mRNA, whereas codon substitutions that impair translation of the mini-ORF have no such effect. These findings suggest that occupancy of SD2 by ribosomes, but not mini-ORF translation, helps to protect espADB mRNA from degradation, likely by hindering RNase E access to the AU-rich leader region.
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Affiliation(s)
- Patricia B Lodato
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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Crabill E, Karpisek A, Alfano JR. The Pseudomonas syringae HrpJ protein controls the secretion of type III translocator proteins and has a virulence role inside plant cells. Mol Microbiol 2012; 85:225-38. [PMID: 22607547 DOI: 10.1111/j.1365-2958.2012.08097.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The bacterial plant pathogen Pseudomonas syringae injects effector proteins into plant cells via a type III secretion system (T3SS), which is required for pathogenesis. The protein HrpJ is secreted by P. syringae and is required for a fully functional T3SS. A hrpJ mutant is non-pathogenic and cannot inject effectors into plant cells or secrete the harpin HrpZ1. Here we show that the hrpJ mutant also cannot secrete the harpins HrpW1 and HopAK1 or the translocator HrpK1, suggesting that these proteins are required in the translocation (injection) of effectors into plant cells. Complementation of the hrpJ mutant with secretion incompetent HrpJ derivatives restores the secretion of HrpZ1 and HrpW1 and the ability to elicit a hypersensitive response, a measure of translocation. However, growth in planta and disease symptom production is only partially restored, suggesting that secreted HrpJ may have a direct role in virulence. Transgenic Arabidopsis plants expressing HrpJ-HA complemented the virulence phenotype of the hrpJ mutant expressing a secretion incompetent HrpJ derivative and were reduced in their immune responses. Collectively, these data indicate that HrpJ has a dual role in P. syringae: inside bacterial cells HrpJ controls the secretion of translocator proteins and inside plant cells it suppresses plant immunity.
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Affiliation(s)
- Emerson Crabill
- Center for Plant Science Innovation, University of Nebraska, Lincoln, NE 68588-0660, USA
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Enterohemorrhagic Escherichia coli virulence regulation by two bacterial adrenergic kinases, QseC and QseE. Infect Immun 2011; 80:688-703. [PMID: 22144490 DOI: 10.1128/iai.05921-11] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7 has two histidine sensor kinases, QseC and QseE, which respond to the mammalian adrenergic hormones epinephrine and norepinephrine by increasing their autophosphorylation. Although QseC and QseE are present in nonpathogenic strains of E. coli, EHEC exploits these kinases for virulence regulation. To further investigate the full extent of epinephrine and its sensors' impact on EHEC virulence, we performed transcriptomic and phenotypic analyses of single and double deletions of qseC and qseE genes in the absence or presence of epinephrine. We showed that in EHEC, epinephrine sensing seems to occur primarily through QseC and QseE. We also observed that QseC and QseE regulate expression of the locus of enterocyte effacement (LEE) genes positively and negatively, respectively. LEE activation, which is required for the formation of the characteristic attaching and effacing (A/E) lesions by EHEC on epithelial cells, is epinephrine dependent. Regulation of the LEE and the non-LEE-contained virulence factor gene nleA by QseE is indirect, through transcription inhibition of the RcsB response regulator. Finally, we show that coincubation of HeLa cells with epinephrine increases EHEC infectivity in a QseC- and QseE-dependent manner. These results genetically and phenotypically map the contributions of the two adrenergic sensors QseC and QseE to EHEC pathogenesis.
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Discovery of novel secreted virulence factors from Salmonella enterica serovar Typhimurium by proteomic analysis of culture supernatants. Infect Immun 2010; 79:33-43. [PMID: 20974834 DOI: 10.1128/iai.00771-10] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica serovar Typhimurium is a leading cause of acute gastroenteritis throughout the world. This pathogen has two type III secretion systems (TTSS) encoded in Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) that deliver virulence factors (effectors) to the host cell cytoplasm and are required for virulence. While many effectors have been identified and at least partially characterized, the full repertoire of effectors has not been catalogued. In this proteomic study, we identified effector proteins secreted into defined minimal medium designed to induce expression of the SPI-2 TTSS and its effectors. We compared the secretomes of the parent strain to those of strains missing essential (ssaK::cat) or regulatory (ΔssaL) components of the SPI-2 TTSS. We identified 20 known SPI-2 effectors. Excluding the translocon components SseBCD, all SPI-2 effectors were biased for identification in the ΔssaL mutant, substantiating the regulatory role of SsaL in TTS. To identify novel effector proteins, we coupled our secretome data with a machine learning algorithm (SIEVE, SVM-based identification and evaluation of virulence effectors) and selected 12 candidate proteins for further characterization. Using CyaA' reporter fusions, we identified six novel type III effectors and two additional proteins that were secreted into J774 macrophages independently of a TTSS. To assess their roles in virulence, we constructed nonpolar deletions and performed a competitive index analysis from intraperitoneally infected 129/SvJ mice. Six mutants were significantly attenuated for spleen colonization. Our results also suggest that non-type III secretion mechanisms are required for full Salmonella virulence.
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Martinez-Argudo I, Blocker AJ. The Shigella T3SS needle transmits a signal for MxiC release, which controls secretion of effectors. Mol Microbiol 2010. [PMID: 21143311 DOI: 10.1111/journal.1365-2958.2010.07413.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Type III secretion systems (T3SSs) are key determinants of virulence in many Gram-negative bacteria, including animal and plant pathogens. They inject 'effector' proteins through a 'needle' protruding from the bacterial surface directly into eukaryotic cells after assembly of a 'translocator' pore in the host plasma membrane. Secretion is a tightly regulated process, which is blocked until physical contact with a host cell takes place. Host cell sensing occurs through a distal needle 'tip complex' and translocators are secreted before effectors. MxiC, a Shigella T3SS substrate, prevents premature effector secretion. Here, we examine how the different parts of T3SSs work together to allow orderly secretion. We show that T3SS assembly and needle tip composition are not altered in an mxiC mutant. We find that MxiC not only represses effector secretion but that it is also required for translocator release. We provide genetic evidence that MxiC acts downstream of the tip complex and then the needle during secretion activation. Finally, we show that the needle controls MxiC release. Therefore, for the first time, our data allow us to propose a model of secretion activation that goes from the tip complex to cytoplasmic MxiC via the needle.
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Martinez-Argudo I, Blocker AJ. The Shigella T3SS needle transmits a signal for MxiC release, which controls secretion of effectors. Mol Microbiol 2010; 78:1365-78. [PMID: 21143311 PMCID: PMC3020320 DOI: 10.1111/j.1365-2958.2010.07413.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Type III secretion systems (T3SSs) are key determinants of virulence in many Gram-negative bacteria, including animal and plant pathogens. They inject ‘effector’ proteins through a ‘needle’ protruding from the bacterial surface directly into eukaryotic cells after assembly of a ‘translocator’ pore in the host plasma membrane. Secretion is a tightly regulated process, which is blocked until physical contact with a host cell takes place. Host cell sensing occurs through a distal needle ‘tip complex’ and translocators are secreted before effectors. MxiC, a Shigella T3SS substrate, prevents premature effector secretion. Here, we examine how the different parts of T3SSs work together to allow orderly secretion. We show that T3SS assembly and needle tip composition are not altered in an mxiC mutant. We find that MxiC not only represses effector secretion but that it is also required for translocator release. We provide genetic evidence that MxiC acts downstream of the tip complex and then the needle during secretion activation. Finally, we show that the needle controls MxiC release. Therefore, for the first time, our data allow us to propose a model of secretion activation that goes from the tip complex to cytoplasmic MxiC via the needle.
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22
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SepL resembles an aberrant effector in binding to a class 1 type III secretion chaperone and carrying an N-terminal secretion signal. J Bacteriol 2010; 192:6093-8. [PMID: 20833800 DOI: 10.1128/jb.00760-10] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Here we show that the type III secretion gatekeeper protein SepL resembles an aberrant effector protein in binding to a class 1 type III secretion chaperone (Orf12, here renamed CesL). We also show that short N-terminal fragments (≤70 amino acids) from SepL are capable of targeting fusion proteins for secretion and translocation.
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23
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Timing is everything: the regulation of type III secretion. Cell Mol Life Sci 2009; 67:1065-75. [PMID: 20043184 PMCID: PMC2835726 DOI: 10.1007/s00018-009-0230-0] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2009] [Revised: 11/23/2009] [Accepted: 12/08/2009] [Indexed: 12/19/2022]
Abstract
Type Three Secretion Systems (T3SSs) are essential virulence determinants of many Gram-negative bacteria. The T3SS is an injection device that can transfer bacterial virulence proteins directly into host cells. The apparatus is made up of a basal body that spans both bacterial membranes and an extracellular needle that possesses a channel that is thought to act as a conduit for protein secretion. Contact with a host-cell membrane triggers the insertion of a pore into the target membrane, and effectors are translocated through this pore into the host cell. To assemble a functional T3SS, specific substrates must be targeted to the apparatus in the correct order. Recently, there have been many developments in our structural and functional understanding of the proteins involved in the regulation of secretion. Here we review the current understanding of protein components of the system thought to be involved in switching between different stages of secretion.
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24
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Tree JJ, Wolfson EB, Wang D, Roe AJ, Gally DL. Controlling injection: regulation of type III secretion in enterohaemorrhagic Escherichia coli. Trends Microbiol 2009; 17:361-70. [PMID: 19660954 DOI: 10.1016/j.tim.2009.06.001] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2008] [Revised: 05/25/2009] [Accepted: 06/01/2009] [Indexed: 12/01/2022]
Abstract
Type III secretion (T3S) systems enable the injection of bacterial proteins through membrane barriers into host cells, either from outside the host cell or from within a vacuole. This system is required for colonization of their ruminant reservoir hosts by enterohaemorrhagic Escherichia coli (EHEC) and might also be important for the etiology of disease in the incidental human host. T3S systems of E. coli inject a cocktail of proteins into epithelial cells that enables bacterial attachment and promotes longer-term colonization in the animal. Here, we review recent progress in our understanding of the regulation of T3S in EHEC, focusing on the induction and assembly of the T3S system, the co-ordination of effector protein expression, and the timing of effector protein export through the apparatus. Strain variation is often associated with differences in bacteriophages encoding the production of Shiga toxin and in multiple cryptic prophage elements that can encode effector proteins and T3S regulators. It is evident that this repertoire of phage-related sequences results in the different levels of T3S demonstrated between strains, with implications for EHEC epidemiology and strain evolution.
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Affiliation(s)
- Jai J Tree
- Immunity and Infection Division, The Roslin Institute and R(D)SVS, Chancellor's Building, University of Edinburgh, Edinburgh, EH16 4SB, UK
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25
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The RNA binding protein CsrA is a pleiotropic regulator of the locus of enterocyte effacement pathogenicity island of enteropathogenic Escherichia coli. Infect Immun 2009; 77:3552-68. [PMID: 19581394 DOI: 10.1128/iai.00418-09] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The attaching and effacing (A/E) pathogen enteropathogenic Escherichia coli (EPEC) forms characteristic actin-filled membranous protrusions upon infection of host cells termed pedestals. Here we examine the role of the RNA binding protein CsrA in the expression of virulence genes and proteins that are necessary for pedestal formation. The csrA mutant was defective in forming actin pedestals on epithelial cells and in disrupting transepithelial resistance across polarized epithelial cells. Consistent with reduced pedestal formation, secretion of the translocators EspA, EspB, and EspD and the effector Tir was substantially reduced in the csrA mutant. Purified CsrA specifically bound to the sepL espADB mRNA leader, and the corresponding transcript levels were reduced in the csrA mutant. In contrast, Tir synthesis was unaffected in the csrA mutant. Reduced secretion of Tir appeared to be in part due to decreased synthesis of EscD, an inner membrane architectural protein of the type III secretion system (TTSS) and EscF, a protein that forms the protruding needle complex of the TTSS. These effects were not mediated through the locus of enterocyte effacement (LEE) transcriptional regulator GrlA or Ler. In contrast to the csrA mutant, multicopy expression of csrA repressed transcription from LEE1, grlRA, LEE2, LEE5, escD, and LEE4, an effect mediated by GrlA and Ler. Consistent with its role in other organisms, CsrA also regulated flagellar motility and glycogen levels. Our findings suggest that CsrA governs virulence factor expression in an A/E pathogen by regulating mRNAs encoding translocators, effectors, or transcription factors.
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26
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Botteaux A, Sory MP, Biskri L, Parsot C, Allaoui A. MxiC is secreted by and controls the substrate specificity of the Shigella flexneri type III secretion apparatus. Mol Microbiol 2008; 71:449-60. [PMID: 19017268 DOI: 10.1111/j.1365-2958.2008.06537.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Many gram-negative pathogenic bacteria use a type III secretion (T3S) system to interact with cells of their hosts. Mechanisms controlling the hierarchical addressing of needle subunits, translocators and effectors to the T3S apparatus (T3SA) are still poorly understood. We investigated the function of MxiC, the member of the YopN/InvE/SepL family in the Shigella flexneri T3S system. Inactivation of mxiC led specifically to a deregulated secretion of effectors (including IpaA, IpgD, IcsB, IpgB2, OspD1 and IpaHs), but not of translocators (IpaB and IpaC) and proteins controlling the T3SA structure or activity (Spa32 and IpaD). Expression of effector-encoding genes controlled by the activity of the T3SA and the transcription activator MxiE was increased in the mxiC mutant, as a consequence of the increased secretion of the MxiE anti-activator OspD1. MxiC is a T3SA substrate and its ability to be secreted is required for its function. By using co-purification assays, we found that MxiC can associate with the Spa47 ATPase, which suggests that MxiC might prevent secretion of effectors by blocking the T3SA from the inside. Although with a 10-fold reduced efficiency compared with the wild-type strain, the mxiC mutant was still able to enter epithelial cells.
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Affiliation(s)
- Anne Botteaux
- Laboratoire de Bactériologie Moléculaire, Faculté de Médecine, Université Libre de Bruxelles, Route de Lennik, 808, CP: 614b, 1070, Brussels, Belgium
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27
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Lodato PB, Kaper JB. Post-transcriptional processing of the LEE4 operon in enterohaemorrhagic Escherichia coli. Mol Microbiol 2008; 71:273-90. [PMID: 19019141 DOI: 10.1111/j.1365-2958.2008.06530.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Enterohaemorrhagic Escherichia coli (EHEC) employs a type III secretion system (T3SS) to export translocator and effector proteins required for mucosal colonization. The T3SS is encoded in a pathogenicity island called the locus of enterocyte effacement (LEE) that is organized in five major operons, LEE1 to LEE5. LEE4 encodes a regulator of secretion (SepL), translocators (EspA, D and B), two chaperones (CesD2 and L0017), a T3SS component (EscF) and an effector protein (EspF). It was originally proposed that the esp transcript is transcribed from a promoter located at the end of sepL but other authors suggested that this transcript is the result of a post-transcriptional processing event. In this study, we established that the espADB mRNA is generated by post-transcriptional processing at the end of the sepL coding sequence. RNase E is the endonuclease involved in the cleavage, but the interaction of this enzyme with other proteins through its C-terminal half is dispensable. A putative transcription termination event in the cesD2 coding region would generate the 3' end of the transcript. Similar to what has been described for other processed transcripts, the cleavage of LEE4 seems a mechanism to differentially regulate SepL and Esp protein production.
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Affiliation(s)
- Patricia B Lodato
- Center for Vaccine Development and Department of Microbiology and Immunology, University of Maryland School of Medicine, 685 W. Baltimore St, Baltimore, MD 21201, USA
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28
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Wang D, Roe AJ, McAteer S, Shipston MJ, Gally DL. Hierarchal type III secretion of translocators and effectors from Escherichia coli O157:H7 requires the carboxy terminus of SepL that binds to Tir. Mol Microbiol 2008; 69:1499-512. [PMID: 18673458 DOI: 10.1111/j.1365-2958.2008.06377.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
SUMMARY Type III secretion (T3S) from enteric bacteria is a co-ordinated process with a hierarchy of secreted proteins. In enteropathogenic and enterohaemorrhagic Escherichia coli, SepL and SepD are essential for translocator but not effector protein export, but how they function to control this differential secretion is not known. This study has focused on the different activities of SepL including membrane localization, SepD binding, EspD export and Tir secretion regulation. Analyses of SepL truncates demonstrated that the different functions associated with SepL can be separated. In particular, SepL with a deletion of 11 amino acids from the C-terminus was able to localize to the bacterial membrane, export translocon proteins but not regulate Tir or other effector protein secretion. From the repertoire of effector proteins only Tir was shown to bind directly to full-length SepL and the C-terminal 48 amino acids of SepL was sufficient to interact with Tir. By synchronizing induction of T3S, it was evident that the Tir-binding capacity of SepL is important to delay the release of effector proteins while the EspADB translocon is secreted. The interaction between Tir and SepL is therefore a critical step that controls the timing of T3S in attaching and effacing pathogens.
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Affiliation(s)
- Dai Wang
- Immunity and Infection Division, The Roslin Institute and R(D)SVS, Chancellor's Building, University of Edinburgh, Edinburgh, EH16 4SB, UK
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29
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Vareille M, Rannou F, Thélier N, Glasser AL, de Sablet T, Martin C, Gobert AP. Heme Oxygenase-1 Is a Critical Regulator of Nitric Oxide Production in EnterohemorrhagicEscherichia coli-Infected Human Enterocytes. THE JOURNAL OF IMMUNOLOGY 2008; 180:5720-6. [DOI: 10.4049/jimmunol.180.8.5720] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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30
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Deane JE, Roversi P, King C, Johnson S, Lea SM. Structures of the Shigella flexneri type 3 secretion system protein MxiC reveal conformational variability amongst homologues. J Mol Biol 2008; 377:985-92. [PMID: 18304577 PMCID: PMC2724173 DOI: 10.1016/j.jmb.2008.01.072] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Revised: 01/14/2008] [Accepted: 01/16/2008] [Indexed: 12/24/2022]
Abstract
Many Gram-negative pathogenic bacteria use a complex macromolecular machine, known as the type 3 secretion system (T3SS), to transfer virulence proteins into host cells. The T3SS is composed of a cytoplasmic bulb, a basal body spanning the inner and outer bacterial membranes, and an extracellular needle. Secretion is regulated by both cytoplasmic and inner membrane proteins that must respond to specific signals in order to ensure that virulence proteins are not secreted before contact with a eukaryotic cell. This negative regulation is mediated, in part, by a family of proteins that are thought to physically block the entrance to the secretion apparatus until an appropriate signal is received following host cell contact. Despite weak sequence homology between proteins of this family, the crystal structures of Shigella flexneri MxiC we present here confirm the conservation of domain topology with the homologue from Yersinia sp. Interestingly, comparison of the Shigella and Yersinia structures reveals a significant structural change that results in substantial domain re-arrangement and opening of one face of the molecule. The conservation of a negatively charged patch on this face suggests it may have a role in binding other components of the T3SS.
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Affiliation(s)
- Janet E Deane
- Sir William Dunn School of Pathology, South Parks Rd, University of Oxford, Oxford OX1 3RE, UK
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31
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Gobert AP, Coste A, Guzman CA, Vareille M, Hindré T, de Sablet T, Girardeau JP, Martin C. Modulation of chemokine gene expression by Shiga-toxin producing Escherichia coli belonging to various origins and serotypes. Microbes Infect 2007; 10:159-65. [PMID: 18248761 DOI: 10.1016/j.micinf.2007.10.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Revised: 10/31/2007] [Accepted: 10/31/2007] [Indexed: 01/11/2023]
Abstract
Infection with Shiga-toxin producing Escherichia coli (STEC) may result in the development of the haemolytic-uremic syndrome (HUS), the main cause of acute renal failure in children. While O157:H7 STEC are associated with large outbreaks of HUS, it is difficult to predict whether a non-O157:H7 isolate can be pathogenic for humans. The mucosal innate immune response plays a central role in the pathogenesis of HUS; therefore, we compared the induction of IL-8 and CCL20 in human colon epithelial cells infected with strains belonging to different serotypes, isolated from cattle or from HUS patients. No correlation was observed between strain virulence and chemokine gene expression. Rather, the genetic background of the strains seems to determine the chemokine gene expression profile. Investigating the contribution of different bacterial factors in this process, we show that the type III secretion system of O157:H7 bacteria, but not the intimate adhesion, is required to stimulate the cells. In addition, H7, H10, and H21 flagellins are potent inducers of chemokine gene expression when synthesized in large amount.
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Affiliation(s)
- Alain P Gobert
- Institut National de la Recherche Agronomique (INRA), UR454 Unité de Microbiologie, Centre de Theix, 63122 Saint-Genès-Champanelle, France.
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32
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Li M, Rosenshine I, Yu HB, Nadler C, Mills E, Hew CL, Leung KY. Identification and characterization of NleI, a new non-LEE-encoded effector of enteropathogenic Escherichia coli (EPEC). Microbes Infect 2006; 8:2890-8. [PMID: 17097322 DOI: 10.1016/j.micinf.2006.09.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2006] [Revised: 09/25/2006] [Accepted: 09/25/2006] [Indexed: 12/28/2022]
Abstract
Enteropathogenic Escherichia coli (EPEC), a major gastrointestinal pathogen, causes infantile diarrhea in many developing countries. EPEC is an attaching and effacing (A/E) pathogen that utilizes a LEE-encoded type III secretion system (TTSS) to deliver effector proteins into host cells. These effectors have been identified as potential virulence factors in A/E pathogens including EPEC, enterohemorrhagic E. coli (EHEC) and Citrobacter rodentium (CR). We used a proteomics approach to identify a new non-LEE-encoded effector, NleI, from the EPEC sepL and sepD mutants. The nleI gene, located in a prophage-associated island with nleBCD, is also present in EHEC and CR but not in E. coli K-12. In EPEC, the transcription of nleI was increased upon sepD inactivation but remained unaffected in ler and sepL mutants. We demonstrated that NleI is secreted and translocated into HeLa cells in a TTSS-dependent manner and that the CesT chaperone is required for efficient NleI translocation. Nevertheless, under overexpression conditions, the first 20 amino acids of NleI are sufficient to support both secretion and translocation. After translocation, NleI can be detected in the cytoplasmic and membrane of HeLa cells.
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Affiliation(s)
- Mo Li
- Department of Biological Sciences, National University of Singapore, Science Drive 4, 117543 Singapore, Singapore
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Patel A, Cummings N, Batchelor M, Hill PJ, Dubois T, Mellits KH, Frankel G, Connerton I. Host protein interactions with enteropathogenic Escherichia coli (EPEC): 14-3-3tau binds Tir and has a role in EPEC-induced actin polymerization. Cell Microbiol 2006; 8:55-71. [PMID: 16367866 DOI: 10.1111/j.1462-5822.2005.00600.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Enteropathogenic Escherichia coli (EPEC) cause infantile diarrhoea and are characterized by their ability to produce attaching and effacing lesions on the surface of intestinal epithelial cells. EPEC employ a filamentous type III secretion system to deliver effector molecules that subvert mammalian cell function to generate actin- and cytokeratin-rich pedestals beneath adherent bacteria. Tir is a major effector protein that is delivered to the plasma membrane of the eukaryotic cell where it acts as the receptor for the bacterial adhesin intimin. Host cell proteins that are recruited to the site of intimate attachment include focal adhesion and cytoskeletal proteins that contribute to pedestal formation. We have used Tir as bait in a yeast two-hybrid screen to identify the protein 14-3-3tau as a binding partner. 14-3-3 proteins are a family of adaptor proteins that modulate protein function in all eukaryotic cells. Here we demonstrate that the tau isoform (also known as theta) of 14-3-3 can bind specifically to Tir in a phosphorylation-independent manner, and that the interaction occurs during the infection process by co-immunoprecipitation of the partners from infected HeLa cell extracts. 14-3-3tau is recruited to the site of the pedestal (3 h after infection) and can decorate attached EPEC in the later stages of the infection process (5-7 h). Pedestal formation can be impaired by depletion of cellular 14-3-3tau using small interfering RNAs. This study indicates a direct functional role for the 14-3-3tau:Tir interaction and is the first to demonstrate the association of a host protein with the surface of EPEC.
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Affiliation(s)
- Amit Patel
- Division of Food Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leics LE12 5RD, UK
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Naylor SW, Roe AJ, Nart P, Spears K, Smith DGE, Low JC, Gally DL. Escherichia coli O157 : H7 forms attaching and effacing lesions at the terminal rectum of cattle and colonization requires the LEE4 operon. MICROBIOLOGY-SGM 2005; 151:2773-2781. [PMID: 16079353 DOI: 10.1099/mic.0.28060-0] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Enterohaemorrhagic Escherichia coli O157 : H7 is a human pathogen that causes no apparent disease in cattle, its primary reservoir host. Recent research has demonstrated that E. coli O157 : H7 predominately colonizes the distal few centimetres of the bovine rectum, and in this study, the LEE4 operon encoding a type III secretion system translocon and associated proteins was shown to be essential for colonization. A deletion mutant of LEE4 failed to colonize cattle, in contrast to a co-inoculated strain containing a chromosomal complement of the operon, therefore fulfilling 'molecular' Koch's postulates for this virulence determinant. In addition, attaching and effacing (A/E) lesions were detectable in E. coli O157 : H7 microcolonies from the terminal rectum of both naturally and experimentally colonized cattle when examined by transmission electron microscopy. This study proves that type III secretion is required for colonization of cattle by E. coli O157 : H7, and that A/E lesion formation occurs at the bovine terminal rectum within E. coli O157 : H7 microcolonies. The research confirms the value of using type III secreted proteins as vaccine candidates in cattle.
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Affiliation(s)
- Stuart W Naylor
- Animal Health Group, Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, UK
| | - Andrew J Roe
- Zoonotic and Animal Pathogens Research Laboratory, Division of Veterinary Biomedical Sciences, Teviot Place, Edinburgh University, Edinburgh EH8 9AG, UK
| | - Pablo Nart
- Zoonotic and Animal Pathogens Research Laboratory, Division of Veterinary Biomedical Sciences, Teviot Place, Edinburgh University, Edinburgh EH8 9AG, UK
- Animal Health Group, Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, UK
| | - Kevin Spears
- Zoonotic and Animal Pathogens Research Laboratory, Division of Veterinary Biomedical Sciences, Teviot Place, Edinburgh University, Edinburgh EH8 9AG, UK
| | - David G E Smith
- Functional Genomics Unit, Moredun Research Institute, Pentland Science Park, Mid Lothian EH26 0PZ, UK
| | - J Christopher Low
- Animal Health Group, Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, UK
| | - David L Gally
- Zoonotic and Animal Pathogens Research Laboratory, Division of Veterinary Biomedical Sciences, Teviot Place, Edinburgh University, Edinburgh EH8 9AG, UK
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Thomas NA, Deng W, Puente JL, Frey EA, Yip CK, Strynadka NCJ, Finlay BB. CesT is a multi-effector chaperone and recruitment factor required for the efficient type III secretion of both LEE- and non-LEE-encoded effectors of enteropathogenicEscherichia coli. Mol Microbiol 2005; 57:1762-79. [PMID: 16135239 DOI: 10.1111/j.1365-2958.2005.04802.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Enteropathogenic Escherichia coli (EPEC) is an intestinal attaching and effacing pathogen that utilizes a type III secretion system (T3SS) for the delivery of effectors into host cells. The chaperone CesT has been shown to bind and stabilize the type III translocated effectors Tir and Map in the bacterial cytoplasm prior to their delivery into host cells. In this study we demonstrate a role for CesT in effector recruitment to the membrane embedded T3SS. CesT-mediated effector recruitment was dependent on the presence of the T3SS membrane-associated ATPase EscN. EPEC DeltacesT carrying a C-terminal CesT variant, CesT(E142G), exhibited normal cytoplasmic Tir stability function, but was less efficient in secreting Tir, further implicating CesT in type III secretion. In vivo co-immunoprecipitation studies using CesT-FLAG containing EPEC lysates demonstrated that CesT interacts with Tir and EscN, consistent with the notion of CesT recruiting Tir to the T3SS. CesT was also shown to be required for the efficient secretion of several type III effectors encoded within and outside the locus of enterocyte effacement (LEE) in addition to Tir and Map. Furthermore, a CesT affinity column was shown to specifically retain multiple effector proteins from EPEC culture supernatants. These findings indicate that CesT is centrally involved in recruiting multiple type III effectors to the T3SS via EscN for efficient secretion, and functionally redefine the role of CesT in multiple type III effector interactions.
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Affiliation(s)
- Nikhil A Thomas
- Michael Smith Laboratories, University of British Columbia, Vancouver, BC, Canada
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36
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Deng W, Li Y, Hardwidge PR, Frey EA, Pfuetzner RA, Lee S, Gruenheid S, Strynakda NCJ, Puente JL, Finlay BB. Regulation of type III secretion hierarchy of translocators and effectors in attaching and effacing bacterial pathogens. Infect Immun 2005; 73:2135-46. [PMID: 15784556 PMCID: PMC1087438 DOI: 10.1128/iai.73.4.2135-2146.2005] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Human enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and the mouse pathogen Citrobacter rodentium (CR) belong to the family of attaching and effacing (A/E) bacterial pathogens. They possess the locus of enterocyte effacement (LEE) pathogenicity island, which encodes a type III secretion system. These pathogens secrete a number of proteins into culture media, including type III effector proteins and translocators that are required for the translocation of effectors into host cells. Preliminary evidence indicated that the LEE-encoded SepL and Rorf6/SepD may form a molecular switch that controls the secretion of translocators and effectors in CR. Here, we show that SepL and SepD indeed perform this function in A/E pathogens such as EHEC and EPEC. Their sepL and sepD mutants do not secrete translocators but exhibit enhanced secretion of effectors. We demonstrate that SepL and SepD interact with each other and that both SepL and SepD are localized to the bacterial membranes. Furthermore, we demonstrate that culture media influence the type III secretion profile of EHEC, EPEC, and CR and that low-calcium concentrations inhibit secretion of translocators but promote the secretion of effectors, similar to effects on type III secretion by mutations in sepL and sepD. However, the secretion profile of the sepD and sepL mutants is not affected by these culture conditions. Collectively, our results suggest that SepL and SepD not only are necessary for efficient translocator secretion in A/E pathogens but also control a switch from translocator to effector secretion by sensing certain environmental signals such as low calcium.
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Affiliation(s)
- Wanyin Deng
- Michael Smith Laboratories, University of British Columbia, 301-2185, East Mall, Vancouver, British Columbia V6T 1Z4, Canada
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Pallen MJ, Beatson SA, Bailey CM. Bioinformatics, genomics and evolution of non-flagellar type-III secretion systems: a Darwinian perpective. FEMS Microbiol Rev 2005; 29:201-29. [PMID: 15808742 DOI: 10.1016/j.femsre.2005.01.001] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2004] [Revised: 12/22/2004] [Accepted: 01/06/2005] [Indexed: 12/17/2022] Open
Abstract
We review the biology of non-flagellar type-III secretion systems from a Darwinian perspective, highlighting the themes of evolution, conservation, variation and decay. The presence of these systems in environmental organisms such as Myxococcus, Desulfovibrio and Verrucomicrobium hints at roles beyond virulence. We review newly discovered sequence homologies (e.g., YopN/TyeA and SepL). We discuss synapomorphies that might be useful in formulating a taxonomy of type-III secretion. The problem of information overload is likely to be ameliorated by launch of a web site devoted to the comparative biology of type-III secretion ().
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Affiliation(s)
- Mark J Pallen
- Bacterial Pathogenesis and Genomics Unit, Division of Immunity and Infection, Medical School, University of Birmingham, Birmingham, West Midlands B15 2TT, UK.
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Ritchie JM, Waldor MK. The locus of enterocyte effacement-encoded effector proteins all promote enterohemorrhagic Escherichia coli pathogenicity in infant rabbits. Infect Immun 2005; 73:1466-74. [PMID: 15731044 PMCID: PMC1064977 DOI: 10.1128/iai.73.3.1466-1474.2005] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The genes encoding the enterohemorrhagic Escherichia coli (EHEC) type III secretion system (TTSS) and five effector proteins secreted by the TTSS are located on the locus of enterocyte effacement (LEE) pathogenicity island. Deletion of tir, which encodes one of these effector proteins, results in a profound reduction (approximately 10,000-fold) in EHEC colonization of the infant rabbit intestine, but the in vivo phenotypes of other LEE genes are unknown. Here, we constructed in-frame deletions in escN, the putative ATPase component of the TTSS, and the genes encoding the four other LEE-encoded effector proteins, EspH, Map, EspF, and EspG, to investigate the contributions of the TTSS and the translocated effector proteins to EHEC pathogenicity in infant rabbits. We found that the TTSS is required for EHEC colonization and attaching and effacing (A/E) lesion formation in the rabbit intestine. Deletion of escN reduced EHEC recovery from the rabbit intestine by approximately 10,000-fold. Although EspH, Map, EspF, and EspG were not required for A/E lesion formation in the rabbit intestine or in HeLa cells, these effector proteins promote EHEC colonization. Colonization by the espH and espF mutants was reduced throughout the intestine. In contrast, colonization by the map and espG mutants was reduced only in the small intestine, indicating that Map and EspG have organ-specific effects. EspF appears to down-regulate the host response to EHEC, since we observed increased accumulation of polymorphonuclear leukocytes in the colonic mucosa of rabbits infected with the EHEC espF mutant. Thus, all the known LEE-encoded effector proteins influence EHEC pathogenicity.
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Affiliation(s)
- Jennifer M Ritchie
- Department of Microbiology, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111, USA
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Pallen MJ, Beatson SA, Bailey CM. Bioinformatics analysis of the locus for enterocyte effacement provides novel insights into type-III secretion. BMC Microbiol 2005; 5:9. [PMID: 15757514 PMCID: PMC1084347 DOI: 10.1186/1471-2180-5-9] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Accepted: 03/09/2005] [Indexed: 12/17/2022] Open
Abstract
Background Like many other pathogens, enterohaemorrhagic and enteropathogenic strains of Escherichia coli employ a type-III secretion system to translocate bacterial effector proteins into host cells, where they then disrupt a range of cellular functions. This system is encoded by the locus for enterocyte effacement. Many of the genes within this locus have been assigned names and functions through homology with the better characterised Ysc-Yop system from Yersinia spp. However, the functions and homologies of many LEE genes remain obscure. Results We have performed a fresh bioinformatics analysis of the LEE. Using PSI-BLAST we have been able to identify several novel homologies between LEE-encoded and Ysc-Yop-associated proteins: Orf2/YscE, Orf5/YscL, rORF8/EscI, SepQ/YscQ, SepL/YopN-TyeA, CesD2/LcrR. In addition, we highlight homology between EspA and flagellin, and report many new homologues of the chaperone CesT. Conclusion We conclude that the vast majority of LEE-encoded proteins do indeed possess homologues and that homology data can be used in combination with experimental data to make fresh functional predictions.
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Affiliation(s)
- Mark J Pallen
- Bacterial Pathogenesis and Genomics Unit, Division of Immunity and Infection, Medical School, University of Birmingham, Birmingham, B15 2TT, UK
| | - Scott A Beatson
- Bacterial Pathogenesis and Genomics Unit, Division of Immunity and Infection, Medical School, University of Birmingham, Birmingham, B15 2TT, UK
| | - Christopher M Bailey
- Bacterial Pathogenesis and Genomics Unit, Division of Immunity and Infection, Medical School, University of Birmingham, Birmingham, B15 2TT, UK
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40
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Sharma VK, Zuerner RL. Role of hha and ler in transcriptional regulation of the esp operon of enterohemorrhagic Escherichia coli O157:H7. J Bacteriol 2004; 186:7290-301. [PMID: 15489441 PMCID: PMC523200 DOI: 10.1128/jb.186.21.7290-7301.2004] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The locus of enterocyte effacement (LEE), which includes five major operons (LEE1 through LEE4 and tir), enables enterohemorrhagic Escherichia coli (EHEC) O157:H7 to produce attaching and effacing lesions on host cells. Expression of LEE2, LEE3, and tir is positively regulated by ler, a gene located in LEE1. Transcriptional regulation of the esp operon (LEE4), however, is not well defined. Transposon mutagenesis was used to identify transcriptional regulators of the esp operon by screening for mutants with increased beta-galactosidase activity in an EHEC O157:H7 strain harboring an esp::lac transcriptional fusion. All mutants with significant increases in beta-galactosidase activity had transposon insertions in hha (hha::Tn). Specific complementation of the hha::Tn mutation with a plasmid-encoded copy of hha reduced beta-galactosidase activity to the level expressed in the parental esp::lac strain. Purified Hha, however, bound poorly to the esp promoter, suggesting that Hha might repress the transcription of a positive regulator of esp. Transposon mutagenesis of a Deltahha esp::lac strain expressing elevated levels of beta-galactosidase resulted in ler mutants with reduced beta-galactosidase activity. Purified Hha bound to the ler promoter with a higher affinity, and complementation of a Deltahha mutation in a Deltahha ler::lac strain repressed beta-galactosidase activity to the level expressed in a ler::lac strain. A positive regulatory role of ler in esp expression was demonstrated by specific binding of Ler to the esp promoter, reduced expression of beta-galactosidase in Deltaler esp::lac strains with and without hha, and severalfold-increased transcription of ler and espA in strains lacking hha. These results indicate that hha-mediated repression of ler causes reduced expression of the esp operon.
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Affiliation(s)
- Vijay K Sharma
- National Animal Disease Center, USDA/ARS, P.O. Box 70, Ames, IA 50010, USA.
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41
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Coombes BK, Brown NF, Valdez Y, Brumell JH, Finlay BB. Expression and secretion of Salmonella pathogenicity island-2 virulence genes in response to acidification exhibit differential requirements of a functional type III secretion apparatus and SsaL. J Biol Chem 2004; 279:49804-15. [PMID: 15383528 DOI: 10.1074/jbc.m404299200] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Salmonella pathogenicity island (SPI)-2 is pivotal to the intracellular survival of Salmonella and for virulence in mammals. SPI-2 encodes virulence factors (called effectors) that are translocated into the host cell, a type III secretion apparatus and a two-component regulatory system that regulates intracellular expression of SPI-2. Salmonella SPI-2 secretion activity appears to be induced in response to acidification of the vacuole in which it replicates. Here we show that the expression of the SPI-2 proteins, SseB and SseD (filament and pore forming components of the secretion apparatus, respectively) in response to acidification requires an intact secretion system and SsaL, a Salmonella homologue of SepL, a regulator required for type III-dependent secretion of translocators but not effectors in attaching and effacing gastrointestinal pathogens. We show that the expression of SPI-2-encoded effectors is acid-regulated but can be uncoupled from the expression of filament and translocon components, thus showing a differential requirement of SsaL for expression. The secretion and translocation of SPI-2-encoded effectors requires SsaL, but SsaL is dispensable for the secretion of SPI-2 effectors encoded in other pathogenicity loci, suggesting a secretion regulation function for SsaL. Further, we demonstrate that the differential expression of adjacent genes within the sseA operon (sseD and sseE) occurs at the transcriptional level. These data indicate that a Salmonella SPI-2 activation state is achieved by an acidregulated response that requires SsaL. These data also suggest the existence of a previously unrecognized regulatory element within SPI-2 for the "effector operon" region downstream of sseD that might demarcate the expression of translocators and effectors.
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Affiliation(s)
- Brian K Coombes
- Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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42
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Gruenheid S, Sekirov I, Thomas NA, Deng W, O'Donnell P, Goode D, Li Y, Frey EA, Brown NF, Metalnikov P, Pawson T, Ashman K, Finlay BB. Identification and characterization of NleA, a non-LEE-encoded type III translocated virulence factor of enterohaemorrhagic Escherichia coli O157:H7. Mol Microbiol 2004; 51:1233-49. [PMID: 14982621 DOI: 10.1046/j.1365-2958.2003.03911.x] [Citation(s) in RCA: 178] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 uses a specialized protein translocation apparatus, the type III secretion system (TTSS), to deliver bacterial effector proteins into host cells. These effectors interfere with host cytoskeletal pathways and signalling cascades to facilitate bacterial survival and replication and promote disease. The genes encoding the TTSS and all known type III secreted effectors in EHEC are localized in a single pathogenicity island on the bacterial chromosome known as the locus for enterocyte effacement (LEE). In this study, we performed a proteomic analysis of proteins secreted by the LEE-encoded TTSS of EHEC. In addition to known LEE-encoded type III secreted proteins, such as EspA, EspB and Tir, a novel protein, NleA (non-LEE-encoded effector A), was identified. NleA is encoded in a prophage-associated pathogenicity island within the EHEC genome, distinct from the LEE. The LEE-encoded TTSS directs translocation of NleA into host cells, where it localizes to the Golgi apparatus. In a panel of strains examined by Southern blot and database analyses, nleA was found to be present in all other LEE-containing pathogens examined, including enteropathogenic E. coli and Citrobacter rodentium, and was absent from non-pathogenic strains of E. coli and non-LEE-containing pathogens. NleA was determined to play a key role in virulence of C. rodentium in a mouse infection model.
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Affiliation(s)
- Samantha Gruenheid
- Biotechnology Laboratory, University of British Columbia, Room 237, Wesbrook Building, 6174 University Boulevard, Vancouver, BC, V6T 1Z3, Canada
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43
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O'Connell CB, Creasey EA, Knutton S, Elliott S, Crowther LJ, Luo W, Albert MJ, Kaper JB, Frankel G, Donnenberg MS. SepL, a protein required for enteropathogenic Escherichia coli type III translocation, interacts with secretion component SepD. Mol Microbiol 2004; 52:1613-25. [PMID: 15186412 DOI: 10.1111/j.1365-2958.2004.04101.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Enteropathogenic Escherichia coli (EPEC), an important cause of infantile diarrhoea in the developing world, disrupts host cell microvilli, causes actin rearrangements and attaches intimately to the host cell surface. This characteristic phenotype, referred to as the attaching and effacing (A/E) effect, is encoded on a 36 kb pathogenicity island called the locus of enterocyte effacement (LEE). The LEE includes genes involved in type III secretion and translocation, the eae gene encoding an outer membrane adhesin known as intimin, the tir gene for the translocated intimin receptor, a regulator and various genes of unknown function. Among this last group is sepL. To determine the role of SepL in EPEC pathogenesis, we constructed and tested a non-polar sepL mutant. We found that this sepL mutant is deficient for A/E and that it secretes markedly reduced quantities of those proteins involved in translocation (EspA, EspB and EspD), but normal levels of those proteins presumed to be effectors (Tir, EspF and EspG). Despite normal levels of secretion, the mutant strain was unable to translocate EspF and Tir into host cells and formed no EspA filaments. Fractionation studies revealed that SepL is a soluble cytoplasmic protein. Yeast two-hybrid and affinity purification studies indicated that SepL interacts with the LEE-encoded protein SepD. In contrast to SepL, we found that SepD is required for type III secretion of both translocation and effector proteins. Together, these results demonstrate that SepL has a unique role in type III secretion as a functional component of the translocation system that interacts with an essential element of the secretion machinery.
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Affiliation(s)
- Colin B O'Connell
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201-1192, USA
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44
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Mundy R, Petrovska L, Smollett K, Simpson N, Wilson RK, Yu J, Tu X, Rosenshine I, Clare S, Dougan G, Frankel G. Identification of a novel Citrobacter rodentium type III secreted protein, EspI, and roles of this and other secreted proteins in infection. Infect Immun 2004; 72:2288-302. [PMID: 15039354 PMCID: PMC375195 DOI: 10.1128/iai.72.4.2288-2302.2004] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Citrobacter rodentium is a member of a group of pathogens that colonize the lumen of the host gastrointestinal tract via attaching and effacing (A/E) lesion formation. C. rodentium, which causes transmissible colonic hyperplasia in mice, is used as an in vivo model system for the clinically significant A/E pathogens enterohemorrhagic and enteropathogenic Escherichia coli. These bacteria all contain a pathogenicity island called the locus of enterocyte effacement (LEE), which encodes a type III secretion system that is designed to deliver effector proteins into eukaryotic host cells. These effectors are involved in the subversion of host eukaryotic cell functions to the benefit of the bacterium. In this study we used mutant strains to determine the effects of the C. rodentium LEE-encoded effectors EspF, EspG, EspH, and Map on virulence in the mouse model. In addition, we identified a novel secreted protein, EspI encoded outside the LEE, whose secretion is also dependent on a functional type III secretion system. Mutant strains with each of the effectors investigated were found to be outcompeted by wild-type bacteria in mixed-infection experiments in vivo, although the effects of EspF and EspH were only subtle. In single-infection experiments, we found that EspF, EspG, and EspH are not required for efficient colonization of the mouse colon or for the production of hyperplasia. In contrast, strains producing EspI and Map had significant colonization defects and resulted in dramatically reduced levels of hyperplasia, and they exhibited very different growth dynamics in mice than the wild-type strain exhibited.
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Affiliation(s)
- Rosanna Mundy
- Centre for Molecular Microbiology and Infection, Department of Biological Sciences, Imperial College, London SW7 2AZ, United Kingdom
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45
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Deng W, Puente JL, Gruenheid S, Li Y, Vallance BA, Vázquez A, Barba J, Ibarra JA, O'Donnell P, Metalnikov P, Ashman K, Lee S, Goode D, Pawson T, Finlay BB. Dissecting virulence: systematic and functional analyses of a pathogenicity island. Proc Natl Acad Sci U S A 2004; 101:3597-602. [PMID: 14988506 PMCID: PMC373508 DOI: 10.1073/pnas.0400326101] [Citation(s) in RCA: 497] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2003] [Indexed: 01/08/2023] Open
Abstract
Bacterial pathogenicity islands (PAI) often encode both effector molecules responsible for disease and secretion systems that deliver these effectors to host cells. Human enterohemorrhagic Escherichia coli (EHEC), enteropathogenic E. coli, and the mouse pathogen Citrobacter rodentium (CR) possess the locus of enterocyte effacement (LEE) PAI. We systematically mutagenized all 41 CR LEE genes and functionally characterized these mutants in vitro and in a murine infection model. We identified 33 virulence factors, including two virulence regulators and a hierarchical switch for type III secretion. In addition, 7 potential type III effectors encoded outside the LEE were identified by using a proteomics approach. These non-LEE effectors are encoded by three uncharacterized PAIs in EHEC O157, suggesting that these PAIs act cooperatively with the LEE in pathogenesis. Our findings provide significant insights into bacterial virulence mechanisms and disease.
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Affiliation(s)
- Wanyin Deng
- Biotechnology Laboratory, University of British Columbia, Vancouver, BC, Canada V6T 1Z3
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46
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Lan R, Stevenson G, Reeves PR. Comparison of two major forms of the Shigella virulence plasmid pINV: positive selection is a major force driving the divergence. Infect Immun 2003; 71:6298-306. [PMID: 14573649 PMCID: PMC219609 DOI: 10.1128/iai.71.11.6298-6306.2003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
All Shigella and enteroinvasive Escherichia coli (EIEC) strains carry a 230-kb virulence plasmid (pINV) which is essential for their invasiveness. There are two sequence forms, pINV A and pINV B, of the plasmid (R. Lan, B. Lumb, D. Ryan, and P. R. Reeves, Infect. Immun. 69:6303-6309, 2001), and the recently sequenced pINV plasmid from Shigella flexneri serotype 5 is a pINV B form. In this study we sequenced the majority of the coding region of the pINV A form from S. flexneri serotype 6 other than insertion sequence or related sequences and compared it with the pINV B form. More than half of the genes sequenced appear to be under positive selection based on their low ratio of synonymous to nonsynonymous substitutions. This high proportion of selected differences indicates that the two pINV forms have functional differences, and comparative studies of pathogenicity in different Shigella-EIEC strains could be informative. There are also genes absent in the S. flexneri serotype 6 plasmid, including the sepA gene encoding serine protease, the major secreted protein of S. flexneri serotype 2a, and the stbAB genes, which encode one of the two partition systems found in S. flexneri serotype 5. The incompatibility of the two pINV forms appears to be due to either small differences in the mvpAT postsegregational killing system or the presence of an unknown system in pINVA.
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Affiliation(s)
- Ruiting Lan
- School of Molecular and Microbial Biosciences, University of Sydney, Sydney, Australia
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Roe AJ, Yull H, Naylor SW, Woodward MJ, Smith DGE, Gally DL. Heterogeneous surface expression of EspA translocon filaments by Escherichia coli O157:H7 is controlled at the posttranscriptional level. Infect Immun 2003; 71:5900-9. [PMID: 14500511 PMCID: PMC201059 DOI: 10.1128/iai.71.10.5900-5909.2003] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Type III secretion systems of enteric bacteria enable translocation of effector proteins into host cells. Secreted proteins of verotoxigenic Escherichia coli O157 strains include components of a translocation apparatus, EspA, -B, and -D, as well as "effectors" such as the translocated intimin receptor (Tir) and the mitochondrion-associated protein (Map). This research has investigated the regulation of LEE4 translocon proteins, in particular EspA. EspA filaments could not be detected on the bacterial cell surface when E. coli O157:H7 was cultured in M9 minimal medium but were expressed from only a proportion of the bacterial population when cultured in minimal essential medium modified with 25 mM HEPES. The highest proportions of EspA-filamented bacteria were detected in late exponential phase, after which filaments were lost rapidly from the bacterial cell surface. Our previous research had shown that human and bovine E. coli O157:H7 strains exhibit marked differences in EspD secretion levels. Here it is demonstrated that the proportion of the bacterial population expressing EspA filaments was associated with the level of EspD secretion. The ability of individual bacteria to express EspA filaments was not controlled at the level of LEE1-4 operon transcription, as demonstrated by using both beta-galactosidase and green fluorescent protein (GFP) promoter fusions. All bacteria, whether expressing EspA filaments or not, showed equivalent levels of GFP expression when LEE1-4 translational fusions were used. Despite this, the LEE4-espADB mRNA was more abundant from populations with a high proportion of nonsecreting bacteria (low secretors) than from populations with a high proportion of secreting and therefore filamented bacteria (high secretors). This research demonstrates that while specific environmental conditions are required to induce LEE1-4 expression, a further checkpoint exists before EspA filaments are produced on the bacterial surface and secretion of effector proteins occurs. This checkpoint in E. coli O157:H7 translocon expression is controlled by a posttranscriptional mechanism acting on LEE4-espADB mRNA. The heterogeneity in EspA filamentation could arise from phase-variable expression of regulators that control this posttranscriptional mechanism.
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Affiliation(s)
- Andrew J. Roe
- Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, University of Edinburgh, Edinburgh EH8 9AG, Veterinary Laboratory Agency, Addlestone, Surrey KT15 3NB, United Kingdom
| | - Helen Yull
- Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, University of Edinburgh, Edinburgh EH8 9AG, Veterinary Laboratory Agency, Addlestone, Surrey KT15 3NB, United Kingdom
| | - Stuart W. Naylor
- Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, University of Edinburgh, Edinburgh EH8 9AG, Veterinary Laboratory Agency, Addlestone, Surrey KT15 3NB, United Kingdom
| | - Martin J. Woodward
- Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, University of Edinburgh, Edinburgh EH8 9AG, Veterinary Laboratory Agency, Addlestone, Surrey KT15 3NB, United Kingdom
| | - David G. E. Smith
- Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, University of Edinburgh, Edinburgh EH8 9AG, Veterinary Laboratory Agency, Addlestone, Surrey KT15 3NB, United Kingdom
| | - David L. Gally
- Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, University of Edinburgh, Edinburgh EH8 9AG, Veterinary Laboratory Agency, Addlestone, Surrey KT15 3NB, United Kingdom
- Corresponding author. Mailing address: Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, Teviot Place, University of Edinburgh, Edinburgh EH8 9AG, United Kingdom. Phone: 00 44 131 6511342. Fax: 00 44 131 6506531. E-mail:
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Nagano K, Taguchi K, Hara T, Yokoyama SI, Kawada K, Mori H. Adhesion and colonization of enterohemorrhagic Escherichia coli O157:H7 in cecum of mice. Microbiol Immunol 2003; 47:125-32. [PMID: 12680715 DOI: 10.1111/j.1348-0421.2003.tb02795.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Infectious diseases due to enterohemorrhagic Escherichia coli (EHEC) are characterized by diarrhea, hemorrhagic colitis and hemolytic uremic syndrome. The adherence of EHEC on intestinal epithelial cells is a first step for developing these diseases. In the present study, we examined whether EHEC O157:H7 adhere to intestinal epithelial cells of mice and cause F-actin accumulation in the epithelial cells following the intragastric inoculation of the pathogen. Fecal shedding of the EHEC O157:H7 strain was observed in ICR mice up to 3 weeks. Fecal shedding periods of the type III secretion system-related gene (espA and sepL) deletion mutants were clearly shorter than that of the wild-type EHEC O157:H7 strain. The EHEC O157:H7 colonies were found on the epithelial surfaces of the ceca in association with F-actin accumulation beneath the attached bacteria.
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Affiliation(s)
- Keiji Nagano
- Laboratory of Microbiology, Department of Public Health Pharmacy, Gifu Pharmaceutical University, Gifu, Gifu 502-8585, Japan
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Deiwick J, Rappl C, Stender S, Jungblut PR, Hensel M. Proteomic approaches to Salmonella Pathogenicity Island 2 encoded proteins and the SsrAB regulon. Proteomics 2002; 2:792-9. [PMID: 12112863 DOI: 10.1002/1615-9861(200206)2:6<792::aid-prot792>3.0.co;2-v] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Type III protein secretion is a common virulence determinant in Gram-negative bacteria and the genetic information is often clustered in pathogenicity islands or on virulence plasmids. We have analyzed the type III secretion system encoded by Salmonella Pathogenicity Island 2 (SPI2) that is indispensable for systemic disease of Salmonella enterica serotype Typhimurium (S. Typhimurium) in mice. Since the low abundance of this secretion system restricted direct analysis by proteomic approaches, several putative proteins were expressed as recombinant products and analyzed by two-dimensional electrophoresis. The map obtained for SPI2 encoded proteins was correlated to the expression pattern of S. Typhimurium. The latter was compared to the proteins induced by SsrAB, the two-component system regulating SPI2 gene expression. Our results exemplify that recombinant expression is a complementary tool for analysis of low abundant proteins or membrane proteins. This approach contributes to the characterization of these proteins by subcellular fractionation. Furthermore, we show that pulse labeling was necessary to analyze growth phase regulated SPI2 proteins that might not be otherwise detectable.
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Affiliation(s)
- Jörg Deiwick
- Max von Pettenkofer-Institut, Ludwig-Maximilians-Universität München, Germany.
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Lan R, Lumb B, Ryan D, Reeves PR. Molecular evolution of large virulence plasmid in Shigella clones and enteroinvasive Escherichia coli. Infect Immun 2001; 69:6303-9. [PMID: 11553574 PMCID: PMC98765 DOI: 10.1128/iai.69.10.6303-6309.2001] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Three genes, ipgD, mxiC, and mxiA, all in the invasion region of the Shigella virulence plasmid, were sequenced from strains representing a range of Shigella serotypes and from two enteroinvasive Escherichia coli (EIEC) isolates. The plasmids can be classified into two relatively homogeneous sequence forms which are quite distinct. pINV A plasmids are found in Shigella flexneri strains F6 and F6A, S. boydii strains B1, B4, B9, B10, B14, and B15, S. dysenteriae strains D3, D4, D6, D8, D9, D10, and D13, and the two EIEC strains (M519 and M520). pINV B plasmids are present in S. flexneri strains F1A, F2A, F3A, F3C, F4A, and FY, two S. boydii strains (B11 and B12), and S. sonnei. The D1 pINV plasmid is a recombinant with ipgD gene more closely related to those of pINV A but with mxiA and mxiC genes more closely related to those of pINV B. The phylogenetic relationships of the plasmid and those of the chromosomal genes of Shigella strains are largely consistent. The cluster 1 and cluster 3 strains tested (G.M. Pupo, R. Lan, and P. R. Reeves, Proc. Natl. Acad. Sci. USA 97:10567-10572, 2000) have pINV A and pINV B plasmids, respectively. However, of the three cluster 2 strains (B9, B11, and B15), B9 and B15 have pINV A while B11 has a pINV B plasmid. Those Shigella (D8 and D10 and S. sonnei) and EIEC strains which do not group with the main body of Shigella strains based on chromosomal genes were found to have plasmids belonging to one or the other of the two types and must have acquired these by lateral transfer.
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Affiliation(s)
- R Lan
- Department of Microbiology, The University of Sydney, Sydney, New South Wales 2006, Australia
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