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Seabaugh JA, Anderson DM. Pathogenicity and virulence of Yersinia. Virulence 2024; 15:2316439. [PMID: 38389313 PMCID: PMC10896167 DOI: 10.1080/21505594.2024.2316439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Accepted: 02/04/2024] [Indexed: 02/24/2024] Open
Abstract
The genus Yersinia includes human, animal, insect, and plant pathogens as well as many symbionts and harmless bacteria. Within this genus are Yersinia enterocolitica and the Yersinia pseudotuberculosis complex, with four human pathogenic species that are highly related at the genomic level including the causative agent of plague, Yersinia pestis. Extensive laboratory, field work, and clinical research have been conducted to understand the underlying pathogenesis and zoonotic transmission of these pathogens. There are presently more than 500 whole genome sequences from which an evolutionary footprint can be developed that details shared and unique virulence properties. Whereas the virulence of Y. pestis now seems in apparent homoeostasis within its flea transmission cycle, substantial evolutionary changes that affect transmission and disease severity continue to ndergo apparent selective pressure within the other Yersiniae that cause intestinal diseases. In this review, we will summarize the present understanding of the virulence and pathogenesis of Yersinia, highlighting shared mechanisms of virulence and the differences that determine the infection niche and disease severity.
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Affiliation(s)
- Jarett A. Seabaugh
- Department of Veterinary Pathobiology, University of Missouri, Columbia, USA
| | - Deborah M. Anderson
- Department of Veterinary Pathobiology, University of Missouri, Columbia, USA
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2
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Farag SI, Francis MK, Gurung JM, Wai SN, Stenlund H, Francis MS, Nadeem A. Macrophage innate immune responses delineate between defective translocon assemblies produced by Yersinia pseudotuberculosis YopD mutants. Virulence 2023; 14:2249790. [PMID: 37621095 PMCID: PMC10461508 DOI: 10.1080/21505594.2023.2249790] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 06/11/2023] [Accepted: 08/13/2023] [Indexed: 08/26/2023] Open
Abstract
Translocon pores formed in the eukaryotic cell membrane by a type III secretion system facilitate the translocation of immune-modulatory effector proteins into the host cell interior. The YopB and YopD proteins produced and secreted by pathogenic Yersinia spp. harboring a virulence plasmid-encoded type III secretion system perform this pore-forming translocator function. We had previously characterized in vitro T3SS function and in vivo pathogenicity of a number of strains encoding sited-directed point mutations in yopD. This resulted in the classification of mutants into three different classes based upon the severity of the phenotypic defects. To investigate the molecular and functional basis for these defects, we explored the effectiveness of RAW 264.7 cell line to respond to infection by representative YopD mutants of all three classes. Signature cytokine profiles could separate the different YopD mutants into distinct categories. The activation and suppression of certain cytokines that function as central innate immune response modulators correlated well with the ability of mutant bacteria to alter anti-phagocytosis and programmed cell death pathways. These analyses demonstrated that sub-optimal translocon pores impact the extent and magnitude of host cell responsiveness, and this limits the capacity of pathogenic Yersinia spp. to fortify against attack by both early and late arms of the host innate immune response.
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Affiliation(s)
- Salah I. Farag
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden
| | - Monika K. Francis
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden
| | - Jyoti M. Gurung
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden
| | - Sun Nyunt Wai
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden
- The Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå, Sweden
| | - Hans Stenlund
- Department of Plant Physiology, Umeå Plant Science Centre (UPSC), Umeå University, Umeå, Sweden
- Swedish Metabolomics Centre (SMC), Umeå, Sweden
| | - Matthew S. Francis
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden
| | - Aftab Nadeem
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden
- The Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå, Sweden
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Zhang J, Brodsky IE, Shin S. Yersinia deploys type III-secreted effectors to evade caspase-4 inflammasome activation in human cells. mBio 2023; 14:e0131023. [PMID: 37615436 PMCID: PMC10653943 DOI: 10.1128/mbio.01310-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Accepted: 07/06/2023] [Indexed: 08/25/2023] Open
Abstract
IMPORTANCE Yersinia are responsible for significant disease burden in humans, ranging from recurrent disease outbreaks (yersiniosis) to pandemics (Yersinia pestis plague). Together with rising antibiotic resistance rates, there is a critical need to better understand Yersinia pathogenesis and host immune mechanisms, as this information will aid in developing improved immunomodulatory therapeutics. Inflammasome responses in human cells are less studied relative to murine models of infection, though recent studies have uncovered key differences in inflammasome responses between mice and humans. Here, we dissect human intestinal epithelial cell and macrophage inflammasome responses to Yersinia pseudotuberculosis. Our findings provide insight into species- and cell type-specific differences in inflammasome responses to Yersinia.
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Affiliation(s)
- Jenna Zhang
- Department of Microbiology, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania, USA
| | - Igor E. Brodsky
- Department of Pathobiology, University of Pennsylvania, School of Veterinary Medicine, Philadelphia, Pennsylvania, USA
| | - Sunny Shin
- Department of Microbiology, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania, USA
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4
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Zhang J, Brodsky IE, Shin S. Yersinia Type III-Secreted Effectors Evade the Caspase-4 Inflammasome in Human Cells. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.24.525473. [PMID: 36747770 PMCID: PMC9900831 DOI: 10.1101/2023.01.24.525473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Yersinia are gram-negative zoonotic bacteria that use a type III secretion system (T3SS) to inject Yersinia outer proteins (Yops) into the host cytosol to subvert essential components of innate immune signaling. However, Yersinia virulence activities can elicit activation of inflammasomes, which lead to inflammatory cell death and cytokine release to contain infection. Yersinia activation and evasion of inflammasomes have been characterized in murine macrophages but remain poorly defined in human cells, particularly intestinal epithelial cells (IECs), a primary site of intestinal Yersinia infection. In contrast to murine macrophages, we find that in both human IECs and macrophages, Yersinia pseudotuberculosis T3SS effectors enable evasion of the caspase-4 inflammasome, which senses cytosolic lipopolysaccharide (LPS). The antiphagocytic YopE and YopH, as well as the translocation regulator YopK, were collectively responsible for evading inflammasome activation, in part by inhibiting Yersinia internalization mediated by YadA and β1-integrin signaling. These data provide insight into the mechanisms of Yersinia-mediated inflammasome activation and evasion in human cells, and reveal species-specific differences underlying regulation of inflammasome responses to Yersinia .
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Affiliation(s)
- Jenna Zhang
- Department of Microbiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104
| | - Igor E. Brodsky
- Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania 19104
| | - Sunny Shin
- Department of Microbiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104
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Gupta R, Sharma VK, Gupta J, Ghosh SK. 1,3 Dialkylated Imidazolium Ionic Liquid Causes Interdigitated Domains in a Phospholipid Membrane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:3412-3421. [PMID: 35263113 DOI: 10.1021/acs.langmuir.1c03160] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Amphiphilic imidazolium-based ionic liquids (ILs) have proven their efficacy in altering the membrane integrity and dynamics. The present article investigates the phase-separated domains in a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane induced by 1,3 dialkylated imidazolium IL. Isotherm measurements on DPPC monolayers formed at the air-water interface have shown a decrease in the mean molecular area with the addition of this IL. The positive value of the excess Gibbs free energy of mixing indicates an unfavorable mixing of the IL into the lipid. This leads to IL-induced phase-separated domains in the multilayer of the lipid confirmed by the occurrence of two sets of equidistance peaks in the X-ray reflectivity data. The electron density profile along the surface normal obtained by the swelling method shows the bilayer thickness of the newly formed IL-rich phase to be substantially lower (∼34 Å) than the DPPC phase (∼45.8 Å). This IL-rich phase has been confirmed to be interdigitated, showing an enhanced electron density in the tail region due to the overlapping hydrocarbon chains. Differential scanning calorimetry measurements showed that the incorporation of IL enhances the fluidity of the lipid bilayer. Therefore, the study indicates the formation of an interdigitated phase with a lower order compared to the gel phase in the DPPC membrane supplemented with the IL.
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Affiliation(s)
- Ritika Gupta
- Department of Physics, School of Natural Sciences, Shiv Nadar University, NH 91, Tehsil Dadri, G. B. Nagar, Greater Noida, Uttar Pradesh 201314, India
| | - Veerendra K Sharma
- Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
| | - Jyoti Gupta
- Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
| | - Sajal K Ghosh
- Department of Physics, School of Natural Sciences, Shiv Nadar University, NH 91, Tehsil Dadri, G. B. Nagar, Greater Noida, Uttar Pradesh 201314, India
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Kim J, Fukuto HS, Brown DA, Bliska JB, London E. Effects of host cell sterol composition upon internalization of Yersinia pseudotuberculosis and clustered β1 integrin. J Biol Chem 2017; 293:1466-1479. [PMID: 29197826 DOI: 10.1074/jbc.m117.811224] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 11/29/2017] [Indexed: 11/06/2022] Open
Abstract
Yersinia pseudotuberculosis is a foodborne pathogenic bacterium that causes acute gastrointestinal illness, but its mechanisms of infection are incompletely described. We examined how host cell sterol composition affected Y. pseudotuberculosis uptake. To do this, we depleted or substituted cholesterol in human MDA-MB-231 epithelial cells with various alternative sterols. Decreasing host cell cholesterol significantly reduced pathogen internalization. When host cell cholesterol was substituted with various sterols, only desmosterol and 7-dehydrocholesterol supported internalization. This specificity was not due to sterol dependence of bacterial attachment to host cells, which was similar with all sterols studied. Because a key step in Y. pseudotuberculosis internalization is interaction of the bacterial adhesins invasin and YadA with host cell β1 integrin, we compared the sterol dependence of wildtype Y. pseudotuberculosis internalization with that of Δinv, ΔyadA, and ΔinvΔyadA mutant strains. YadA deletion decreased bacterial adherence to host cells, whereas invasin deletion had no effect. Nevertheless, host cell sterol substitution had a similar effect on internalization of these bacterial deletion strains as on the wildtype bacteria. The ΔinvΔyadA double mutant adhered least to cells and so was not significantly internalized. The sterol structure dependence of Y. pseudotuberculosis internalization differed from that of endocytosis, as monitored using antibody-clustered β1 integrin and previous studies on other proteins, which had a more permissive sterol dependence. This study suggests that agents could be designed to interfere with internalization of Yersinia without disturbing endocytosis.
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Affiliation(s)
- JiHyun Kim
- From the Departments of Biochemistry and Cell Biology and
| | - Hana S Fukuto
- Molecular Genetics and Microbiology and.,Center for Infectious Diseases, Stony Brook University, Stony Brook, New York 11794
| | | | - James B Bliska
- Molecular Genetics and Microbiology and.,Center for Infectious Diseases, Stony Brook University, Stony Brook, New York 11794
| | - Erwin London
- From the Departments of Biochemistry and Cell Biology and
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Ekestubbe S, Bröms JE, Edgren T, Fällman M, Francis MS, Forsberg Å. The Amino-Terminal Part of the Needle-Tip Translocator LcrV of Yersinia pseudotuberculosis Is Required for Early Targeting of YopH and In vivo Virulence. Front Cell Infect Microbiol 2016; 6:175. [PMID: 27995096 PMCID: PMC5136540 DOI: 10.3389/fcimb.2016.00175] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Accepted: 11/21/2016] [Indexed: 12/20/2022] Open
Abstract
Type III secretion systems (T3SS) are dedicated to targeting anti-host effector proteins into the cytosol of the host cell to promote bacterial infection. Delivery of the effectors requires three specific translocator proteins, of which the hydrophilic translocator, LcrV, is located at the tip of the T3SS needle and is believed to facilitate insertion of the two hydrophobic translocators into the host cell membrane. Here we used Yersinia as a model to study the role of LcrV in T3SS mediated intracellular effector targeting. Intriguingly, we identified N-terminal lcrV mutants that, similar to the wild-type protein, efficiently promoted expression, secretion and intracellular levels of Yop effectors, yet they were impaired in their ability to inhibit phagocytosis by J774 cells. In line with this, the YopH mediated dephosphorylation of Focal Adhesion Kinase early after infection was compromised when compared to the wild type strain. This suggests that the mutants are unable to promote efficient delivery of effectors to their molecular targets inside the host cell upon host cell contact. The significance of this was borne out by the fact that the mutants were highly attenuated for virulence in the systemic mouse infection model. Our study provides both novel and significant findings that establish a role for LcrV in early targeting of effectors in the host cell.
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Affiliation(s)
- Sofie Ekestubbe
- Laboratory for Molecular Infection Medicine Sweden, Department of Molecular Biology, Umeå UniversityUmeå, Sweden; Department of Molecular Biology, Umeå Centre for Microbial Research, Umeå UniversityUmeå, Sweden
| | - Jeanette E Bröms
- Department of Clinical Microbiology, Umeå University Umeå, Sweden
| | - Tomas Edgren
- Department of Molecular Biology, Umeå Centre for Microbial Research, Umeå University Umeå, Sweden
| | - Maria Fällman
- Laboratory for Molecular Infection Medicine Sweden, Department of Molecular Biology, Umeå UniversityUmeå, Sweden; Department of Molecular Biology, Umeå Centre for Microbial Research, Umeå UniversityUmeå, Sweden
| | - Matthew S Francis
- Department of Molecular Biology, Umeå Centre for Microbial Research, Umeå University Umeå, Sweden
| | - Åke Forsberg
- Laboratory for Molecular Infection Medicine Sweden, Department of Molecular Biology, Umeå UniversityUmeå, Sweden; Department of Molecular Biology, Umeå Centre for Microbial Research, Umeå UniversityUmeå, Sweden
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Coleman MA, Cappuccio JA, Blanchette CD, Gao T, Arroyo ES, Hinz AK, Bourguet FA, Segelke B, Hoeprich PD, Huser T, Laurence TA, Motin VL, Chromy BA. Expression and Association of the Yersinia pestis Translocon Proteins, YopB and YopD, Are Facilitated by Nanolipoprotein Particles. PLoS One 2016; 11:e0150166. [PMID: 27015536 PMCID: PMC4807764 DOI: 10.1371/journal.pone.0150166] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 02/10/2016] [Indexed: 12/18/2022] Open
Abstract
Yersinia pestis enters host cells and evades host defenses, in part, through interactions between Yersinia pestis proteins and host membranes. One such interaction is through the type III secretion system, which uses a highly conserved and ordered complex for Yersinia pestis outer membrane effector protein translocation called the injectisome. The portion of the injectisome that interacts directly with host cell membranes is referred to as the translocon. The translocon is believed to form a pore allowing effector molecules to enter host cells. To facilitate mechanistic studies of the translocon, we have developed a cell-free approach for expressing translocon pore proteins as a complex supported in a bilayer membrane mimetic nano-scaffold known as a nanolipoprotein particle (NLP) Initial results show cell-free expression of Yersinia pestis outer membrane proteins YopB and YopD was enhanced in the presence of liposomes. However, these complexes tended to aggregate and precipitate. With the addition of co-expressed (NLP) forming components, the YopB and/or YopD complex was rendered soluble, increasing the yield of protein for biophysical studies. Biophysical methods such as Atomic Force Microscopy and Fluorescence Correlation Spectroscopy were used to confirm that the soluble YopB/D complex was associated with NLPs. An interaction between the YopB/D complex and NLP was validated by immunoprecipitation. The YopB/D translocon complex embedded in a NLP provides a platform for protein interaction studies between pathogen and host proteins. These studies will help elucidate the poorly understood mechanism which enables this pathogen to inject effector proteins into host cells, thus evading host defenses.
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Affiliation(s)
- Matthew A. Coleman
- Lawrence Livermore National Laboratory, Livermore, CA, United States of America, 94550
- University of California Davis, NSF, Center for Biophotonics, Sacramento, CA, United States of America, 95817
- * E-mail: (MAC); (BAC)
| | - Jenny A. Cappuccio
- Humboldt State University, Department of Chemistry, Arcata, CA, United States of America, 95521
| | - Craig D. Blanchette
- Lawrence Livermore National Laboratory, Livermore, CA, United States of America, 94550
| | - Tingjuan Gao
- University of California Davis, NSF, Center for Biophotonics, Sacramento, CA, United States of America, 95817
| | - Erin S. Arroyo
- Lawrence Livermore National Laboratory, Livermore, CA, United States of America, 94550
| | - Angela K. Hinz
- Lawrence Livermore National Laboratory, Livermore, CA, United States of America, 94550
| | - Feliza A. Bourguet
- Lawrence Livermore National Laboratory, Livermore, CA, United States of America, 94550
| | - Brent Segelke
- Lawrence Livermore National Laboratory, Livermore, CA, United States of America, 94550
| | - Paul D. Hoeprich
- Lawrence Livermore National Laboratory, Livermore, CA, United States of America, 94550
| | - Thomas Huser
- University of California Davis, NSF, Center for Biophotonics, Sacramento, CA, United States of America, 95817
| | - Ted A. Laurence
- Lawrence Livermore National Laboratory, Livermore, CA, United States of America, 94550
| | - Vladimir L. Motin
- University of Texas Medical Branch, Galveston, TX, United States of America, 77555
| | - Brett A. Chromy
- University of California Davis, NSF, Center for Biophotonics, Sacramento, CA, United States of America, 95817
- * E-mail: (MAC); (BAC)
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Ji H, Dong H. Key steps in type III secretion system (T3SS) towards translocon assembly with potential sensor at plant plasma membrane. MOLECULAR PLANT PATHOLOGY 2015; 16:762-73. [PMID: 25469869 PMCID: PMC6638502 DOI: 10.1111/mpp.12223] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Many plant- and animal-pathogenic Gram-negative bacteria employ the type III secretion system (T3SS) to translocate effector proteins from bacterial cells into the cytosol of eukaryotic host cells. The effector translocation occurs through an integral component of T3SS, the channel-like translocon, assembled by hydrophilic and hydrophobic proteinaceous translocators in a two-step process. In the first, hydrophilic translocators localize to the tip of a proteinaceous needle in animal pathogens, or a proteinaceous pilus in plant pathogens, and associate with hydrophobic translocators, which insert into host plasma membranes in the second step. However, the pilus needs to penetrate plant cell walls in advance. All hydrophilic translocators so far identified in plant pathogens are characteristic of harpins: T3SS accessory proteins containing a unitary hydrophilic domain or an additional enzymatic domain. Two-domain harpins carrying a pectate lyase domain potentially target plant cell walls and facilitate the penetration of the pectin-rich middle lamella by the bacterial pilus. One-domain harpins target plant plasma membranes and may play a crucial role in translocon assembly, which may also involve contrapuntal associations of hydrophobic translocators. In all cases, sensory components in the target plasma membrane are indispensable for the membrane recognition of translocators and the functionality of the translocon. The conjectural sensors point to membrane lipids and proteins, and a phosphatidic acid and an aquaporin are able to interact with selected harpin-type translocators. Interactions between translocators and their sensors at the target plasma membrane are assumed to be critical for translocon assembly.
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Affiliation(s)
- Hongtao Ji
- Department of Plant Pathology, Nanjing Agricultural University, Nanjing, 210095, Jiangsu Province, China
| | - Hansong Dong
- Department of Plant Pathology, Nanjing Agricultural University, Nanjing, 210095, Jiangsu Province, China
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10
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Solomon R, Zhang W, McCrann G, Bliska JB, Viboud GI. Random mutagenesis identifies a C-terminal region of YopD important for Yersinia type III secretion function. PLoS One 2015; 10:e0120471. [PMID: 25807250 PMCID: PMC4433470 DOI: 10.1371/journal.pone.0120471] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 01/22/2015] [Indexed: 11/19/2022] Open
Abstract
A common virulence mechanism among bacterial pathogens is the use of specialized secretion systems that deliver virulence proteins through a translocation channel inserted in the host cell membrane. During Yersinia infection, the host recognizes the type III secretion system mounting a pro-inflammatory response. However, soon after they are translocated, the effectors efficiently counteract that response. In this study we sought to identify YopD residues responsible for type III secretion system function. Through random mutagenesis, we identified eight Y. pseudotuberculosis yopD mutants with single amino acid changes affecting various type III secretion functions. Three severely defective mutants had substitutions in residues encompassing a 35 amino acid region (residues 168-203) located between the transmembrane domain and the C-terminal putative coiled-coil region of YopD. These mutations did not affect regulation of the low calcium response or YopB-YopD interaction but markedly inhibited MAPK and NFκB. [corrected] activation. When some of these mutations were introduced into the native yopD gene, defects in effector translocation and pore formation were also observed. We conclude that this newly identified region is important for YopD translocon function. The role of this domain in vivo remains elusive, as amino acid substitutions in that region did not significantly affect virulence of Y. pseudotuberculosis in orogastrically-infected mice.
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Affiliation(s)
- Rebecca Solomon
- Clinical Laboratory Science, School of Health, Technology and Management, Stony Brook University, Stony Brook, New York, United States of America
- Department of Molecular Genetics and Microbiology, Center for Infectious Diseases, School of Medicine, Stony Brook University, Stony Brook, New York, United States of America
| | - Weibing Zhang
- Clinical Laboratory Science, School of Health, Technology and Management, Stony Brook University, Stony Brook, New York, United States of America
- Department of Molecular Genetics and Microbiology, Center for Infectious Diseases, School of Medicine, Stony Brook University, Stony Brook, New York, United States of America
| | - Grace McCrann
- Clinical Laboratory Science, School of Health, Technology and Management, Stony Brook University, Stony Brook, New York, United States of America
| | - James B. Bliska
- Department of Molecular Genetics and Microbiology, Center for Infectious Diseases, School of Medicine, Stony Brook University, Stony Brook, New York, United States of America
| | - Gloria I. Viboud
- Clinical Laboratory Science, School of Health, Technology and Management, Stony Brook University, Stony Brook, New York, United States of America
- Department of Molecular Genetics and Microbiology, Center for Infectious Diseases, School of Medicine, Stony Brook University, Stony Brook, New York, United States of America
- * E-mail:
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11
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Adams W, Morgan J, Kwuan L, Auerbuch V. Yersinia pseudotuberculosis YopD mutants that genetically separate effector protein translocation from host membrane disruption. Mol Microbiol 2015; 96:764-78. [PMID: 25684661 DOI: 10.1111/mmi.12970] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/11/2015] [Indexed: 12/20/2022]
Abstract
The Yersinia type III secretion system (T3SS) translocates Yop effector proteins into host cells to manipulate immune defenses such as phagocytosis and reactive oxygen species (ROS) production. The T3SS translocator proteins YopB and YopD form pores in host membranes, facilitating Yop translocation. While the YopD amino and carboxy termini participate in pore formation, the role of the YopD central region between amino acids 150-227 remains unknown. We assessed the contribution of this region by generating Y. pseudotuberculosis yopD(Δ150-170) and yopD(Δ207-227) mutants and analyzing their T3SS functions. These strains exhibited wild-type levels of Yop secretion in vitro and enabled robust pore formation in macrophages. However, the yopDΔ150-170 and yopD(Δ207-227) mutants were defective in Yop translocation into CHO cells and splenocyte-derived neutrophils and macrophages. These data suggest that YopD-mediated host membrane disruption and effector Yop translocation are genetically separable activities requiring distinct protein domains. Importantly, the yopD(Δ150-170) and yopD(Δ207-227) mutants were defective in Yop-mediated inhibition of macrophage cell death and ROS production in neutrophil-like cells, and were attenuated in disseminated Yersinia infection. Therefore, the ability of the YopD central region to facilitate optimal effector protein delivery into phagocytes, and therefore robust effector Yop function, is important for Yersinia virulence.
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Affiliation(s)
- Walter Adams
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Jessica Morgan
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Laura Kwuan
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Victoria Auerbuch
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, CA, USA
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12
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Wang X, Parashar K, Sitaram A, Bliska JB. The GAP activity of type III effector YopE triggers killing of Yersinia in macrophages. PLoS Pathog 2014; 10:e1004346. [PMID: 25165815 PMCID: PMC4148447 DOI: 10.1371/journal.ppat.1004346] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 07/17/2014] [Indexed: 12/28/2022] Open
Abstract
The mammalian immune system has the ability to discriminate between pathogens and innocuous microbes by detecting conserved molecular patterns. In addition to conserved microbial patterns, the mammalian immune system may recognize distinct pathogen-induced processes through a mechanism which is poorly understood. Previous studies have shown that a type III secretion system (T3SS) in Yersinia pseudotuberculosis leads to decreased survival of this bacterium in primary murine macrophages by unknown mechanisms. Here, we use colony forming unit assays and fluorescence microscopy to investigate how the T3SS triggers killing of Yersinia in macrophages. We present evidence that Yersinia outer protein E (YopE) delivered by the T3SS triggers intracellular killing response against Yersinia. YopE mimics eukaryotic GTPase activating proteins (GAPs) and inactivates Rho GTPases in host cells. Unlike wild-type YopE, catalytically dead YopER144A is impaired in restricting Yersinia intracellular survival, highlighting that the GAP activity of YopE is detected as a danger signal. Additionally, a second translocated effector, YopT, counteracts the YopE triggered killing effect by decreasing the translocation level of YopE and possibly by competing for the same pool of Rho GTPase targets. Moreover, inactivation of Rho GTPases by Clostridium difficile Toxin B mimics the effect of YopE and promotes increased killing of Yersinia in macrophages. Using a Rac inhibitor NSC23766 and a Rho inhibitor TAT-C3, we show that macrophages restrict Yersinia intracellular survival in response to Rac1 inhibition, but not Rho inhibition. In summary, our findings reveal that primary macrophages sense manipulation of Rho GTPases by Yersinia YopE and actively counteract pathogenic infection by restricting intracellular bacterial survival. Our results uncover a new mode of innate immune recognition in response to pathogenic infection. The type III secretion system (T3SS) is a macromolecular protein export pathway found in gram-negative bacteria. It delivers bacterial toxins into eukaryotic cells to promote pathogenic infection. T3SSs and the bacterial toxins delivered are critical arsenals for many bacterial pathogens of clinical significance, such as Yersinia, Salmonella and Shigella. On the other hand, the mammalian immune system may recognize the T3SS as a danger signal to signify pathogenic infection, and to stimulate appropriate defense against pathogens. Here, we show that the innate immune system recognizes the activity of YopE delivered by the Yersinia T3SS. Modulation of host Rho GTPases by YopE elicits a defensive response, which results in killing of bacteria in host cells. Inhibition of host Rho GTPases by Clostridium difficile Toxin B, another bacterial toxin, mimics the YopE-triggered killing effect. Our study demonstrates that host cells sense manipulation of Rho GTPases by bacterial toxins as a surveillance mechanism, revealing new insights into innate immune recognition of pathogenic infections.
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Affiliation(s)
- Xiaoying Wang
- Department of Molecular Genetics and Microbiology, Center for Infectious Diseases, Stony Brook University, Stony Brook, New York, United States of America
| | - Kaustubh Parashar
- Department of Molecular Genetics and Microbiology, Center for Infectious Diseases, Stony Brook University, Stony Brook, New York, United States of America
| | - Ananya Sitaram
- Department of Molecular Genetics and Microbiology, Center for Infectious Diseases, Stony Brook University, Stony Brook, New York, United States of America
| | - James B. Bliska
- Department of Molecular Genetics and Microbiology, Center for Infectious Diseases, Stony Brook University, Stony Brook, New York, United States of America
- * E-mail:
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IQGAP1 is important for activation of caspase-1 in macrophages and is targeted by Yersinia pestis type III effector YopM. mBio 2014; 5:e01402-14. [PMID: 24987096 PMCID: PMC4161239 DOI: 10.1128/mbio.01402-14] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
YopM is a leucine-rich repeat (LRR)-containing effector in several Yersinia species, including Yersinia pestis and Y. pseudotuberculosis. Different Yersinia strains encode distinct YopM isoforms with variable numbers of LRRs but conserved C-terminal tails. A 15-LRR isoform in Y. pseudotuberculosis YPIII was recently shown to bind and inhibit caspase-1 via a YLTD motif in LRR 10, and attenuation of YopM− YPIII was reversed in mice lacking caspase-1, indicating that caspase-1 inhibition is a major virulence function of YopMYPIII. To determine if other YopM proteins inhibit caspase-1, we utilized Y. pseudotuberculosis strains natively expressing a 21-LRR isoform lacking the YLTD motif (YopM32777) or ectopically expressing a Y. pestis 15-LRR version with a functional (YopMKIM) or inactivated (YopMKIM D271A) YLTD motif. Results of mouse and macrophage infections with these strains showed that YopM32777, YopMKIM, and YopMKIM D271A inhibit caspase-1 activation, indicating that the YLTD motif is dispensable for this activity. Analysis of YopMKIM deletion variants revealed that LRRs 6 to 15 and the C-terminal tail are required to inhibit caspase-1 activation. YopM32777, YopMKIM, and YopMKIM deletion variants were purified, and binding partners in macrophage lysates were identified. Caspase-1 bound to YopMKIM but not YopM32777. Additionally, YopMKIM bound IQGAP1 and the use of Iqgap1−/− macrophages revealed that this scaffolding protein is important for caspase-1 activation upon infection with YopM−Y. pseudotuberculosis. Thus, while multiple YopM isoforms inhibit caspase-1 activation, their variable LRR domains bind different host proteins to perform this function and the LRRs of YopMKIM target IQGAP1, a novel regulator of caspase-1, in macrophages. Activation of caspase-1, mediated by macromolecular complexes termed inflammasomes, is important for innate immune defense against pathogens. Pathogens can, in turn, subvert caspase-1-dependent responses through the action of effector proteins. For example, the Yersinia effector YopM inhibits caspase-1 activation by arresting inflammasome formation. This caspase-1 inhibitory activity has been studied in a specific YopM isoform, and in this case, the protein was shown to act as a pseudosubstrate to bind and inhibit caspase-1. Different Yersinia strains encode distinct YopM isoforms, many of which lack the pseudosubstrate motif. We studied additional isoforms and found that these YopM proteins inhibit caspase-1 activation independently of a pseudosubstrate motif. We also identified IQGAP1 as a novel binding partner of the Yersinia pestis YopMKIM isoform and demonstrated that IQGAP1 is important for caspase-1 activation in macrophages infected with Yersinia. Thus, this study reveals new insights into inflammasome regulation during Yersinia infection.
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Galán JE, Lara-Tejero M, Marlovits TC, Wagner S. Bacterial type III secretion systems: specialized nanomachines for protein delivery into target cells. Annu Rev Microbiol 2014; 68:415-38. [PMID: 25002086 DOI: 10.1146/annurev-micro-092412-155725] [Citation(s) in RCA: 367] [Impact Index Per Article: 36.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
One of the most exciting developments in the field of bacterial pathogenesis in recent years is the discovery that many pathogens utilize complex nanomachines to deliver bacterially encoded effector proteins into target eukaryotic cells. These effector proteins modulate a variety of cellular functions for the pathogen's benefit. One of these protein-delivery machines is the type III secretion system (T3SS). T3SSs are widespread in nature and are encoded not only by bacteria pathogenic to vertebrates or plants but also by bacteria that are symbiotic to plants or insects. A central component of T3SSs is the needle complex, a supramolecular structure that mediates the passage of the secreted proteins across the bacterial envelope. Working in conjunction with several cytoplasmic components, the needle complex engages specific substrates in sequential order, moves them across the bacterial envelope, and ultimately delivers them into eukaryotic cells. The central role of T3SSs in pathogenesis makes them great targets for novel antimicrobial strategies.
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Affiliation(s)
- Jorge E Galán
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut 06536;
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15
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Discola KF, Förster A, Boulay F, Simorre JP, Attree I, Dessen A, Job V. Membrane and chaperone recognition by the major translocator protein PopB of the type III secretion system of Pseudomonas aeruginosa. J Biol Chem 2013; 289:3591-601. [PMID: 24297169 DOI: 10.1074/jbc.m113.517920] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The type III secretion system is a widespread apparatus used by pathogenic bacteria to inject effectors directly into the cytoplasm of eukaryotic cells. A key component of this highly conserved system is the translocon, a pore formed in the host membrane that is essential for toxins to bypass this last physical barrier. In Pseudomonas aeruginosa the translocon is composed of PopB and PopD, both of which before secretion are stabilized within the bacterial cytoplasm by a common chaperone, PcrH. In this work we characterize PopB, the major translocator, in both membrane-associated and PcrH-bound forms. By combining sucrose gradient centrifugation experiments, limited proteolysis, one-dimensional NMR, and β-lactamase reporter assays on eukaryotic cells, we show that PopB is stably inserted into bilayers with its flexible N-terminal domain and C-terminal tail exposed to the outside. In addition, we also report the crystal structure of the complex between PcrH and an N-terminal region of PopB (residues 51-59), which reveals that PopB lies within the concave face of PcrH, employing mostly backbone residues for contact. PcrH is thus the first chaperone whose structure has been solved in complex with both type III secretion systems translocators, revealing that both molecules employ the same surface for binding and excluding the possibility of formation of a ternary complex. The characterization of the major type III secretion system translocon component in both membrane-bound and chaperone-bound forms is a key step for the eventual development of antibacterials that block translocon assembly.
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Affiliation(s)
- Karen F Discola
- From the Institut de Biologie Structurale, Université Grenoble Alpes, 6 rue Jules Horowitz, 38000 Grenoble, France
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16
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Chatterjee S, Chaudhury S, McShan AC, Kaur K, De Guzman RN. Structure and biophysics of type III secretion in bacteria. Biochemistry 2013; 52:2508-17. [PMID: 23521714 DOI: 10.1021/bi400160a] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Many plant and animal bacterial pathogens assemble a needle-like nanomachine, the type III secretion system (T3SS), to inject virulence proteins directly into eukaryotic cells to initiate infection. The ability of bacteria to inject effectors into host cells is essential for infection, survival, and pathogenesis for many Gram-negative bacteria, including Salmonella, Escherichia, Shigella, Yersinia, Pseudomonas, and Chlamydia spp. These pathogens are responsible for a wide variety of diseases, such as typhoid fever, large-scale food-borne illnesses, dysentery, bubonic plague, secondary hospital infections, and sexually transmitted diseases. The T3SS consists of structural and nonstructural proteins. The structural proteins assemble the needle apparatus, which consists of a membrane-embedded basal structure, an external needle that protrudes from the bacterial surface, and a tip complex that caps the needle. Upon host cell contact, a translocon is assembled between the needle tip complex and the host cell, serving as a gateway for translocation of effector proteins by creating a pore in the host cell membrane. Following delivery into the host cytoplasm, effectors initiate and maintain infection by manipulating host cell biology, such as cell signaling, secretory trafficking, cytoskeletal dynamics, and the inflammatory response. Finally, chaperones serve as regulators of secretion by sequestering effectors and some structural proteins within the bacterial cytoplasm. This review will focus on the latest developments and future challenges concerning the structure and biophysics of the needle apparatus.
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Affiliation(s)
- Srirupa Chatterjee
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66045, USA
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17
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Impact of host membrane pore formation by the Yersinia pseudotuberculosis type III secretion system on the macrophage innate immune response. Infect Immun 2013; 81:905-14. [PMID: 23297383 DOI: 10.1128/iai.01014-12] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type III secretion systems (T3SSs) are used by Gram-negative pathogens to form pores in host membranes and deliver virulence-associated effector proteins inside host cells. In pathogenic Yersinia, the T3SS pore-forming proteins are YopB and YopD. Mammalian cells recognize the Yersinia T3SS, leading to a host response that includes secretion of the inflammatory cytokine interleukin-1β (IL-1β), Toll-like receptor (TLR)-independent expression of the stress-associated transcription factor Egr1 and the inflammatory cytokine tumor necrosis factor alpha (TNF-α), and host cell death. The known Yersinia T3SS effector proteins are dispensable for eliciting these responses, but YopB is essential. Three models describe how the Yersinia T3SS might trigger inflammation: (i) mammalian cells sense YopBD-mediated pore formation, (ii) innate immune stimuli gain access to the host cytoplasm through the YopBD pore, and/or (iii) the YopB-YopD translocon itself or its membrane insertion is proinflammatory. To test these models, we constructed a Yersinia pseudotuberculosis mutant expressing YopD devoid of its predicted transmembrane domain (YopD(ΔTM)) and lacking the T3SS cargo proteins YopHEMOJTN. This mutant formed pores in macrophages, but it could not mediate translocation of effector proteins inside host cells. Importantly, this mutant did not elicit rapid host cell death, IL-1β secretion, or TLR-independent Egr1 and TNF-α expression. These data suggest that YopBD-mediated translocation of unknown T3SS cargo leads to activation of host pathways influencing inflammation, cell death, and response to stress. As the YopD(ΔTM) Y. pseudotuberculosis mutant formed somewhat smaller pores with delayed kinetics, an alternative model is that the wild-type YopB-YopD translocon is specifically sensed by host cells.
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18
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Tomalka AG, Stopford CM, Lee PC, Rietsch A. A translocator-specific export signal establishes the translocator-effector secretion hierarchy that is important for type III secretion system function. Mol Microbiol 2012; 86:1464-81. [PMID: 23121689 DOI: 10.1111/mmi.12069] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/11/2012] [Indexed: 11/29/2022]
Abstract
Type III secretion systems are used by many Gram-negative pathogens to directly deliver effector proteins into the cytoplasm of host cells. To accomplish this, bacteria secrete translocator proteins that form a pore in the host-cell membrane through which the effector proteins are then introduced into the host cell. Evidence from multiple systems indicates that the pore-forming translocator proteins are exported before effectors, but how this secretion hierarchy is established is unclear. Here we used the Pseudomonas aeruginosa translocator protein PopD as a model to identify its export signals. The N-terminal secretion signal and chaperone, PcrH, are required for export under all conditions. Two novel signals in PopD, one proximal to the chaperone binding site and one at the very C-terminus of the protein, are required for export of PopD before effector proteins. These novel export signals establish the translocator-effector secretion hierarchy, which in turn, is critical for the delivery of effectors into host cells.
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Affiliation(s)
- Amanda G Tomalka
- Department of Molecular Biology and Microbiology, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4960, USA
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19
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Protein export according to schedule: architecture, assembly, and regulation of type III secretion systems from plant- and animal-pathogenic bacteria. Microbiol Mol Biol Rev 2012; 76:262-310. [PMID: 22688814 DOI: 10.1128/mmbr.05017-11] [Citation(s) in RCA: 299] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Flagellar and translocation-associated type III secretion (T3S) systems are present in most gram-negative plant- and animal-pathogenic bacteria and are often essential for bacterial motility or pathogenicity. The architectures of the complex membrane-spanning secretion apparatuses of both systems are similar, but they are associated with different extracellular appendages, including the flagellar hook and filament or the needle/pilus structures of translocation-associated T3S systems. The needle/pilus is connected to a bacterial translocon that is inserted into the host plasma membrane and mediates the transkingdom transport of bacterial effector proteins into eukaryotic cells. During the last 3 to 5 years, significant progress has been made in the characterization of membrane-associated core components and extracellular structures of T3S systems. Furthermore, transcriptional and posttranscriptional regulators that control T3S gene expression and substrate specificity have been described. Given the architecture of the T3S system, it is assumed that extracellular components of the secretion apparatus are secreted prior to effector proteins, suggesting that there is a hierarchy in T3S. The aim of this review is to summarize our current knowledge of T3S system components and associated control proteins from both plant- and animal-pathogenic bacteria.
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20
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The Pseudomonas aeruginosa type III secretion system has an exotoxin S/T/Y independent pathogenic role during acute lung infection. PLoS One 2012; 7:e41547. [PMID: 22844497 PMCID: PMC3402384 DOI: 10.1371/journal.pone.0041547] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2011] [Accepted: 06/27/2012] [Indexed: 12/21/2022] Open
Abstract
The type III secretion system (T3SS) is a complex nanomachine of many pathogenic Gram-negative bacteria. It forms a proteinaceous channel that is inserted into the host eukaryotic cell membrane for injection of bacterial proteins that manipulate host cell signaling. However, few studies have focused on the effector-independent functions of the T3SS. Using a murine model of acute lung infection with Pseudomonas aeruginosa, an important human opportunistic pathogen, we compared the pathogenicity of mutant bacteria that lack all of the known effector toxins ( ΔSTY), with mutant bacteria that also lack the major translocator protein PopB (ΔSTY/ΔPopB) and so cannot form a functional T3SS channel in the host cell membrane. Mortality was higher among mice challenged with ΔSTY compared to mice challenged with ΔSTY/ΔPopB mutant bacteria. In addition, mice infected with ΔSTY showed decreased bacterial clearance from the lungs compared to those infected with ΔSTY/ΔPopB. Infection was in both cases associated with substantial killing of lung infiltrating macrophages. However, macrophages from ΔSTY-infected mice died by pro-inflammatory necrosis characterized by membrane permeabilization and caspase-1 mediated IL-1β production, whereas macrophages from ΔSTY/ΔPopB infected mice died by apoptosis, which is characterized by annexin V positive staining of the cell membrane and caspase-3 activation. This was confirmed in macrophages infected in vitro. These results demonstrate a T3SS effector toxin independent role for the T3SS, in particular the T3SS translocator protein PopB, in the pathogenicity of P. aeruginosa during acute lung infection.
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Type III secretion system-dependent translocation of ectopically expressed Yop effectors into macrophages by intracellular Yersinia pseudotuberculosis. Infect Immun 2011; 79:4322-31. [PMID: 21844228 DOI: 10.1128/iai.05396-11] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Yersinia pseudotuberculosis is a Gram-negative bacterial pathogen. Virulence in Y. pseudotuberculosis requires the plasmid-encoded Ysc type III secretion system (T3SS), which functions to translocate a set of effectors called Yops into infected host cells. The effectors function to antagonize phagocytosis (e.g., YopH) or to induce apoptosis (YopJ) in macrophages infected with Y. pseudotuberculosis. Additionally, when antiphagocytosis is incomplete and Y. pseudotuberculosis is internalized by macrophages, the bacterium can survive in phagosomes. Previous studies have shown that delivery of effectors into host cells occurs efficiently when Yersinia is extracellular. However, it is not clear whether the T3SS can be utilized by intracellular Y. pseudotuberculosis to translocate Yops. This possibility was investigated here using Y. pseudotuberculosis strains that express YopJ or YopH under the control of an inducible promoter. Bone marrow-derived murine macrophages were infected with these strains under conditions that prevented the survival of extracellular bacteria. Effector translocation was detected by measuring apoptosis or the activities of Yop-β-lactamase fusion proteins. Results showed that macrophages underwent apoptosis when YopJ expression was induced prior to phagocytosis, confirming that delivery of this effector prior to or during uptake is sufficient to cause cell death. However, macrophages also underwent apoptosis when YopJ was ectopically expressed after phagocytosis; furthermore, expression of the translocator YopB from intracellular bacteria also resulted in increased cell death. Analysis by microscopy showed that translocation of ectopically expressed YopH- or YopJ-β-lactamase fusions could be correlated with the presence of viable Y. pseudotuberculosis in macrophages. Collectively, our results suggest that the Ysc T3SS of Y. pseudotuberculosis can function within macrophage phagosomes to translocate Yops into the host cytosol.
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Thorslund SE, Edgren T, Pettersson J, Nordfelth R, Sellin ME, Ivanova E, Francis MS, Isaksson EL, Wolf-Watz H, Fällman M. The RACK1 signaling scaffold protein selectively interacts with Yersinia pseudotuberculosis virulence function. PLoS One 2011; 6:e16784. [PMID: 21347310 PMCID: PMC3037380 DOI: 10.1371/journal.pone.0016784] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2010] [Accepted: 01/13/2011] [Indexed: 01/06/2023] Open
Abstract
Many gram-negative bacteria use type III secretion systems to translocate effector proteins into host cells. These effectors interfere with cellular functions in a highly regulated manner resulting in effects that are beneficial for the bacteria. The pathogen Yersinia can resist phagocytosis by eukaryotic cells by translocating Yop effectors into the target cell cytoplasm. This is called antiphagocytosis, and constitutes an important virulence feature of this pathogen since it allows survival in immune cell rich lymphoid organs. We show here that the virulence protein YopK has a role in orchestrating effector translocation necessary for productive antiphagocytosis. We present data showing that YopK influences Yop effector translocation by modulating the ratio of the pore-forming proteins YopB and YopD in the target cell membrane. Further, we show that YopK that can interact with the translocators, is exposed inside target cells and binds to the eukaryotic signaling protein RACK1. This protein is engaged upon Y. pseudotuberculosis-mediated β1-integrin activation and localizes to phagocytic cups. Cells with downregulated RACK1 levels are protected from antiphagocytosis. This resistance is not due to altered levels of translocated antiphagocytic effectors, and cells with reduced levels of RACK1 are still sensitive to the later occurring cytotoxic effect caused by the Yop effectors. Further, a yopK mutant unable to bind RACK1 shows an avirulent phenotype during mouse infection, suggesting that RACK1 targeting by YopK is a requirement for virulence. Together, our data imply that the local event of Yersinia-mediated antiphagocytosis involves a step where YopK, by binding RACK1, ensures an immediate specific spatial delivery of antiphagocytic effectors leading to productive inhibition of phagocytosis.
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Affiliation(s)
- Sara E. Thorslund
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden
| | - Tomas Edgren
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden
| | | | - Roland Nordfelth
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden
| | | | | | - Matthew S. Francis
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden
| | - Elin L. Isaksson
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden
| | - Hans Wolf-Watz
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden
| | - Maria Fällman
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden
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Matteï PJ, Faudry E, Job V, Izoré T, Attree I, Dessen A. Membrane targeting and pore formation by the type III secretion system translocon. FEBS J 2010; 278:414-26. [PMID: 21182592 DOI: 10.1111/j.1742-4658.2010.07974.x] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The type III secretion system (T3SS) is a complex macromolecular machinery employed by a number of Gram-negative species to initiate infection. Toxins secreted through the system are synthesized in the bacterial cytoplasm and utilize the T3SS to pass through both bacterial membranes and the periplasm, thus being introduced directly into the eukaryotic cytoplasm. A key element of the T3SS of all bacterial pathogens is the translocon, which comprises a pore that is inserted into the membrane of the target cell, allowing toxin injection. Three macromolecular partners associate to form the translocon: two are hydrophobic and one is hydrophilic, and the latter also associates with the T3SS needle. In this review, we discuss recent advances on the biochemical and structural characterization of the proteins involved in translocon formation, as well as their participation in the modification of intracellular signalling pathways upon infection. Models of translocon assembly and regulation are also discussed.
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Affiliation(s)
- Pierre-Jean Matteï
- Bacterial Pathogenesis Group, Institut de Biologie Structurale, UMR 5075 (CNRS/CEA/UJF), Grenoble, France
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24
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Brodsky IE, Palm NW, Sadanand S, Ryndak MB, Sutterwala FS, Flavell RA, Bliska JB, Medzhitov R. A Yersinia effector protein promotes virulence by preventing inflammasome recognition of the type III secretion system. Cell Host Microbe 2010; 7:376-87. [PMID: 20478539 DOI: 10.1016/j.chom.2010.04.009] [Citation(s) in RCA: 209] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2009] [Revised: 01/31/2010] [Accepted: 04/09/2010] [Indexed: 12/14/2022]
Abstract
Bacterial pathogens utilize pore-forming toxins or specialized secretion systems to deliver virulence factors to modulate host cell physiology and promote bacterial replication. Detection of these secretion systems or toxins, or their activities, by nucleotide-binding oligomerization domain leucine-rich repeat proteins (NLRs) triggers the assembly of inflammasomes, multiprotein complexes necessary for caspase-1 activation and host defense. Here we demonstrate that caspase-1 activation in response to the Yersinia type III secretion system (T3SS) requires the adaptor ASC and involves both NLRP3 and NLRC4 inflammasomes. Further, we identify a Yersinia type III secreted effector protein, YopK, which interacts with the T3SS translocon to prevent cellular recognition of the T3SS and inflammasome activation. In the absence of YopK, inflammasome sensing of the T3SS promotes bacterial clearance from infected tissues in vivo. These data demonstrate that a class of bacterial proteins interferes with cellular recognition of bacterial secretion systems and contributes to bacterial survival within host tissues.
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Affiliation(s)
- Igor E Brodsky
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06520, USA.
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25
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Septic shock and nonpulmonary organ dysfunction in pneumonic plague: The role of Yersinia pestis pCD1− vs. pgm− virulence factors. Crit Care Med 2010; 38:1574-83. [DOI: 10.1097/ccm.0b013e3181de8ace] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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26
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Costa TRD, Edqvist PJ, Bröms JE, Ahlund MK, Forsberg A, Francis MS. YopD self-assembly and binding to LcrV facilitate type III secretion activity by Yersinia pseudotuberculosis. J Biol Chem 2010; 285:25269-84. [PMID: 20525687 DOI: 10.1074/jbc.m110.144311] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
YopD-like translocator proteins encoded by several Gram-negative bacteria are important for type III secretion-dependent delivery of anti-host effectors into eukaryotic cells. This probably depends on their ability to form pores in the infected cell plasma membrane, through which effectors may gain access to the cell interior. In addition, Yersinia YopD is a negative regulator essential for the control of effector synthesis and secretion. As a prerequisite for this functional duality, YopD may need to establish molecular interactions with other key T3S components. A putative coiled-coil domain and an alpha-helical amphipathic domain, both situated in the YopD C terminus, may represent key protein-protein interaction domains. Therefore, residues within the YopD C terminus were systematically mutagenized. All 68 mutant bacteria were first screened in a variety of assays designed to identify individual residues essential for YopD function, possibly by providing the interaction interface for the docking of other T3S proteins. Mirroring the effect of a full-length yopD gene deletion, five mutant bacteria were defective for both yop regulatory control and effector delivery. Interestingly, all mutations clustered to hydrophobic amino acids of the amphipathic domain. Also situated within this domain, two additional mutants rendered YopD primarily defective in the control of Yop synthesis and secretion. Significantly, protein-protein interaction studies revealed that functionally compromised YopD variants were also defective in self-oligomerization and in the ability to engage another translocator protein, LcrV. Thus, the YopD amphipathic domain facilitates the formation of YopD/YopD and YopD/LcrV interactions, two critical events in the type III secretion process.
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Affiliation(s)
- Tiago R D Costa
- Department of Molecular Biology and Umeå Center for Microbial Research, Umeå University, SE-901 87 Umeå, Sweden
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Wang JH, Zhou YJ, Tian L, He P. Phosphoinositide 3-kinase/Akt and nuclear factor-kappaB are involved in Staphylococcus aureus-induced apoptosis in U937 cells. ACTA ACUST UNITED AC 2010; 24:231-5. [PMID: 20120770 DOI: 10.1016/s1001-9294(10)60007-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
OBJECTIVE To explore the mechanisms involved in Staphylococcus aureus (S. aureus) invading human monocytic U937 cells. METHODS S. aureus were added to U937 cells at multiplicity of infections (MOI) of 20:1 for 0, 15, 30, 60, and 90 minutes, respectively. Cell apoptosis was analyzed with Hoechst 33258 staining and Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) flow cytometry analysis. Akt and nuclear factor-kappaB (NF-kappaB) activities were detected by Western blotting. RESULTS Infection of U937 cells with S. aureus induced rapid cell death in a time-dependent manner, and the cells displayed characteristic features of apoptosis. S. aureus-induced apoptosis was associated with a prominent downregulation of activated (phosphorylated) Akt and NF-kappaB. The inhibition of phosphorylated Akt by LY294002 led to the inhibition of NF-kappaB in a dose-dependent manner. Inhibition of Akt with LY294002 caused further increase in apoptosis of U937 cells. CONCLUSIONS S. aureus can stimulate the apoptosis of U937 cells. S. aureus induces apoptosis of U937 cells by inhibiting Akt-regulated NF-kappaB.
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Affiliation(s)
- Jia-he Wang
- Department of Geriatrics, Shengjing Hospital, China Medical University, Shenyang 110004, China.
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Tan YW, Yu HB, Sivaraman J, Leung KY, Mok YK. Mapping of the chaperone AcrH binding regions of translocators AopB and AopD and characterization of oligomeric and metastable AcrH-AopB-AopD complexes in the type III secretion system of Aeromonas hydrophila. Protein Sci 2009; 18:1724-34. [PMID: 19530229 DOI: 10.1002/pro.187] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
In the type III secretion system (T3SS) of Aeromonas hydrophila, AcrH acts as a chaperone for translocators AopB and AopD. AcrH forms a stable 1:1 monomeric complex with AopD, whereas the 1:1 AcrH-AopB complex exists mainly as a metastable oligomeric form and only in minor amounts as a stable monomeric form. Limited protease digestion shows that these complexes contain highly exposed regions, thus allowing mapping of intact functional chaperone binding regions of AopB and AopD. AopD uses the transmembrane domain (DF1, residues 16-147) and the C-terminal amphipathic helical domain (DF2, residues 242-296) whereas AopB uses a discrete region containing the transmembrane domain and the putative N-terminal coiled coil domain (BF1, residues 33-264). Oligomerization of the AcrH-AopB complex is mainly through the C-terminal coiled coil domain of AopB, which is dispensable for chaperone binding. The three proteins, AcrH, AopB, and AopD, can be coexpressed to form an oligomeric and metastable complex. These three proteins are also oligomerized mainly through the C-terminal domain of AopB. Formation of such an oligomeric and metastable complex may be important for the proper formation of translocon of correct topology and stoichiometry on the host membrane.
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Affiliation(s)
- Yih Wan Tan
- Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore
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Saier MH, Ma CH, Rodgers L, Tamang DG, Yen MR. Protein secretion and membrane insertion systems in bacteria and eukaryotic organelles. ADVANCES IN APPLIED MICROBIOLOGY 2009; 65:141-97. [PMID: 19026865 DOI: 10.1016/s0065-2164(08)00606-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Milton H Saier
- Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093-0116, USA
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Vaccination of mice with a Yop translocon complex elicits antibodies that are protective against infection with F1- Yersinia pestis. Infect Immun 2008; 76:5181-90. [PMID: 18765742 DOI: 10.1128/iai.00189-08] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Yersinia pestis, the bacterial agent of plague, secretes several proteins important for pathogenesis or host protection. The F1 protein forms a capsule on the bacterial cell surface and is a well-characterized protective antigen but is not essential for virulence. A type III secretion system that is essential for virulence exports Yop proteins, which function as antiphagocytic or anti-inflammatory factors. Yop effectors (e.g., YopE) are delivered across the host cell plasma membrane by a translocon, composed of YopB and YopD. Complexes of YopB, YopD, and YopE (BDE) secreted by Yersinia pseudotuberculosis were purified by affinity chromatography and used as immunogens to determine if antibodies to the translocon could provide protection against Y. pestis in mice. Mice vaccinated with BDE generated high-titer immunoglobulin G antibodies specific for BDE, as shown by enzyme-linked immunosorbent assay and immunoblotting, and were protected against lethal intravenous challenge with F1(-) but not F1(+) Y. pestis. Mice passively immunized with anti-BDE serum were protected from lethal challenge with F1(-) Y. pestis. The YopB protein or a complex of YopB and YopD (BD) was purified and determined by vaccination to be immunogenic in mice. Mice actively vaccinated with BD or passively vaccinated with anti-BD serum were protected against lethal challenge with F1(-) Y. pestis. These results indicate that anti-translocon antibodies can be used as immunotherapy to treat infections by F1(-) Y. pestis.
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Limiting too much of a good thing: a negative feedback mechanism prevents unregulated translocation of type III effector proteins. J Bacteriol 2007; 190:2643-4. [PMID: 18083800 DOI: 10.1128/jb.01905-07] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
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Mandal CC, Gayen S, Basu A, Ghosh KS, Dasgupta S, Maiti MK, Sen SK. Prediction-based protein engineering of domain I of Cry2A entomocidal toxin of Bacillus thuringiensis for the enhancement of toxicity against lepidopteran insects. Protein Eng Des Sel 2007; 20:599-606. [DOI: 10.1093/protein/gzm058] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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ExoS controls the cell contact-mediated switch to effector secretion in Pseudomonas aeruginosa. J Bacteriol 2007; 190:2726-38. [PMID: 18039770 DOI: 10.1128/jb.01553-07] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Type III secretion is used by many gram-negative bacterial pathogens to directly deliver protein toxins (effectors) into targeted host cells. In all cases, secretion of effectors is triggered by host cell contact, although the mechanism is unclear. In Pseudomonas aeruginosa, expression of all type III secretion-related genes is up-regulated when secretion is triggered. We were able to visualize this process using a green fluorescent protein reporter system and to use it to monitor the ability of bacteria to trigger effector secretion on cell contact. Surprisingly, the action of one of the major type III secreted effectors, ExoS, prevented triggering of type III secretion by bacteria that subsequently attached to cells, suggesting that triggering of secretion is feedback regulated. Evidence is presented that translocation (secretion of effectors across the host cell plasma membrane) of ExoS is indeed self-regulated and that this inhibition of translocation can be achieved by either of its two enzymatic activities. The translocator proteins PopB, PopD, and PcrV are secreted via the type III secretion system and are required for pore formation and translocation of effectors across the host cell plasma membrane. Here we present data that secretion of translocators is in fact not controlled by calcium, implying that triggering of effector secretion on cell contact represents a switch in secretion specificity, rather than a triggering of secretion per se. The requirement for a host cell cofactor to control effector secretion may help explain the recently observed phenomenon of target cell specificity in both the Yersinia and P. aeruginosa type III secretion systems.
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Saier MH. Protein Secretion and Membrane Insertion Systems in Gram-Negative Bacteria. J Membr Biol 2007; 214:75-90. [PMID: 17546510 DOI: 10.1007/s00232-006-0049-7] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2006] [Revised: 11/07/2006] [Indexed: 12/30/2022]
Abstract
In contrast to other organisms, gram-negative bacteria have evolved numerous systems for protein export. Eight types are known that mediate export across or insertion into the cytoplasmic membrane, while eight specifically mediate export across or insertion into the outer membrane. Three of the former secretory pathway (SP) systems, type I SP (ISP, ABC), IIISP (Fla/Path) and IVSP (Conj/Vir), can export proteins across both membranes in a single energy-coupled step. A fourth generalized mechanism for exporting proteins across the two-membrane envelope in two distinct steps (which we here refer to as type II secretory pathways [IISP]) utilizes either the general secretory pathway (GSP or Sec) or the twin-arginine targeting translocase for translocation across the inner membrane, and either the main terminal branch or one of several protein-specific export systems for translocation across the outer membrane. We here survey the various well-characterized protein translocation systems found in living organisms and then focus on the systems present in gram-negative bacteria. Comparisons between these systems suggest specific biogenic, mechanistic and evolutionary similarities as well as major differences.
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Affiliation(s)
- Milton H Saier
- Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, USA.
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Meyer D, Cunnac S, Guéneron M, Declercq C, Van Gijsegem F, Lauber E, Boucher C, Arlat M. PopF1 and PopF2, two proteins secreted by the type III protein secretion system of Ralstonia solanacearum, are translocators belonging to the HrpF/NopX family. J Bacteriol 2006; 188:4903-17. [PMID: 16788199 PMCID: PMC1483002 DOI: 10.1128/jb.00180-06] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ralstonia solanacearum GMI1000 is a gram-negative plant pathogen which contains an hrp gene cluster which codes for a type III protein secretion system (TTSS). We identified two novel Hrp-secreted proteins, called PopF1 and PopF2, which display similarity to one another and to putative TTSS translocators, HrpF and NopX, from Xanthomonas spp. and rhizobia, respectively. They also show similarities with TTSS translocators of the YopB family from animal-pathogenic bacteria. Both popF1 and popF2 belong to the HrpB regulon and are required for the interaction with plants, but PopF1 seems to play a more important role in virulence and hypersensitive response (HR) elicitation than PopF2 under our experimental conditions. PopF1 and PopF2 are not necessary for the secretion of effector proteins, but they are required for the translocation of AvrA avirulence protein into tobacco cells. We conclude that PopF1 and PopF2 are type III translocators belonging to the HrpF/NopX family. The hrpF gene of Xanthomonas campestris pv. campestris partially restored HR-inducing ability to popF1 popF2 mutants of R. solanacearum, suggesting that translocators of R. solanacearum and Xanthomonas are functionally conserved. Finally, R. solanacearum strain UW551, which does not belong to the same phylotype as GMI1000, also possesses two putative translocator proteins. However, although one of these proteins is clearly related to PopF1 and PopF2, the other seems to be different and related to NopX proteins, thus showing that translocators might be variable in R. solanacearum.
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Affiliation(s)
- Damien Meyer
- Laboratoire des Interactions Plantes-Microorganismes, INRA-CNRS, BP52627, 31326 Castanet tolosan Cedex, France
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Fadl AA, Galindo CL, Sha J, Erova TE, Houston CW, Olano JP, Chopra AK. Deletion of the genes encoding the type III secretion system and cytotoxic enterotoxin alters host responses to Aeromonas hydrophila infection. Microb Pathog 2006; 40:198-210. [PMID: 16626931 DOI: 10.1016/j.micpath.2006.01.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Revised: 01/09/2006] [Accepted: 01/16/2006] [Indexed: 12/21/2022]
Abstract
In our previous study, we deleted the gene encoding Aeromonas outer membrane protein B (AopB), a structural component of the type III secretion system (T3SS) from a cytotoxic enterotoxin gene (act)-minus diarrheal isolate SSU of Aeromonas hydrophila. Our laboratory also molecularly characterized the cytotoxic enterotoxin (Act), which is secreted by the bacterium utilizing the type II secretion system (T2SS). The act/aopB mutant exhibited significantly reduced cytotoxicity to cultured cells (e.g. RAW 264.7 murine macrophages and HT-29 human colonic epithelial cells) and was avirulent in mice. In this study, we developed additional A. hydrophila mutants in which T3SS-associated ascV and acrV genes were deleted, either individually or in combination with that of the act gene, to examine host-pathogen interactions. A significant reduction in the induction of inflammatory cytokines and chemokines was noted in the sera of mice infected with these mutants when compared to animals infected with wild-type (WT) A. hydrophila. After infection with the WT and act/aopB mutant, we performed microarray analyses on RNA from the above-mentioned murine macrophages and human colonic epithelial cells to examine global cellular transcriptional responses. Based on three independent experiments, WT A. hydrophila altered the expression of 434 genes in RAW 264.7 cells and 80 genes in HT-29 cells. Alteration in the expression of 209 macrophage and 32 epithelial cell genes was reduced when the act/aopB mutant was used, compared to when cells were infected with the WT bacterium, indicating the involvement of Act and/or AopB in transcriptional regulation of these genes. We verified up-regulation of 15 genes by real-time reverse transcriptase-polymerase chain reaction and confirmed A. hydrophila WT-versus mutant-induced production of cytokines/chemokines in supernatants from RAW 264.7 and HT-29 cells. This is the first description of host cell transcriptional responses to A. hydrophila infection.
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Affiliation(s)
- Amin A Fadl
- Department of Microbiology and Immunology, The University of Texas Medical Branch, Medical Research Building, 301 University Boulevard, Galveston, TX 77555-1070, USA
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Sha J, Pillai L, Fadl AA, Galindo CL, Erova TE, Chopra AK. The type III secretion system and cytotoxic enterotoxin alter the virulence of Aeromonas hydrophila. Infect Immun 2005; 73:6446-57. [PMID: 16177316 PMCID: PMC1230953 DOI: 10.1128/iai.73.10.6446-6457.2005] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Many gram-negative bacteria use a type III secretion system (TTSS) to deliver effector proteins into host cells. Here we report the characterization of a TTSS chromosomal operon from the diarrheal isolate SSU of Aeromonas hydrophila. We deleted the gene encoding Aeromonas outer membrane protein B (AopB), which is predicted to be involved in the formation of the TTSS translocon, from wild-type (WT) A. hydrophila as well as from a previously characterized cytotoxic enterotoxin gene (act)-minus strain of A. hydrophila, thus generating aopB and act/aopB isogenic mutants. The act gene encodes a type II-secreted cytotoxic enterotoxin (Act) that has hemolytic, cytotoxic, and enterotoxic activities and induces lethality in a mouse model. These isogenic mutants (aopB, act, and act/aopB) were highly attenuated in their ability to induce cytotoxicity in RAW 264.7 murine macrophages and HT-29 human colonic epithelial cells. The act/aopB mutant demonstrated the greatest reduction in cytotoxicity to cultured cells after 4 h of infection, as measured by the release of lactate dehydrogenase enzyme, and was avirulent in mice, with a 90% survival rate compared to that of animals infected with Act and AopB mutants, which caused 50 to 60% of the animals to die at a dose of three 50% lethal doses. In contrast, WT A. hydrophila killed 100% of the mice within 48 h. The effects of these mutations on cytotoxicity could be complemented with the native genes. Our studies further revealed that the production of lactones, which are involved in quorum sensing (QS), was decreased in the act (32%) and aopB (64%) mutants and was minimal (only 8%) in the act/aopB mutant, compared to that of WT A. hydrophila SSU. The effects of act and aopB gene deletions on lactone production could also be complemented with the native genes, indicating specific effects of Act and the TTSS on lactone production. Although recent studies with other bacteria have indicated TTSS regulation by QS, this is the first report describing a correlation between the TTSS and Act of A. hydrophila and the production of lactones.
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Affiliation(s)
- Jian Sha
- Department of Microbiology and Immunology, The University of Texas Medical School Branch, Galveston, 77555-1070, USA
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