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Oh D, Liu X, Sheetz MP, Kenney LJ. Small, Dynamic Clusters of Tir-Intimin Seed Actin Polymerization. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 19:e2302580. [PMID: 37649226 DOI: 10.1002/smll.202302580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 07/26/2023] [Indexed: 09/01/2023]
Abstract
The understanding of actin pedestal formation by enteropathogenic Escherichia coli (EPEC) relies mainly on static ensemble information obtained from cell lysates. Here, the dynamic nature of signaling components on the subsecond timescale, which resemble phase condensates, is demonstrated. Unlike in vitro phase condensates, transfected intimin receptor (Tir) and downstream component form clusters 200 nm in diameter that are spaced ≈500 nm on average, indicating cellular regulation. On supported lipid bilayers with diffusive intimin, Tir-expressing fibroblasts formed Tir-intimin clusters even without Tir tyrosines, although Tir tyrosine phosphorylation is necessary for actin polymerization from clusters. Single-molecule tracking showed that Tir is diffusive in the clusters and exchanges with Tir in the plasma membrane. Further, Nck and N-WASP bind to the clusters and exchange with cytoplasmic molecules. Tir has a similar cluster lifetime to Nck, but longer than that of N-WASP. Actin polymerization from the clusters requires N-WASP binding, involved Arp2/3 activation, and stabilized N-WASP clusters. These dynamic properties are distinct from larger in vitro systems and do not depend significantly upon crosslinking. Thus, Tir-intimin clusters in the plasma membrane are limited in size by exchange and enhance signaling needed for actin polymerization that enables strong and stable bacterial attachment to host cells.
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Affiliation(s)
- Dongmyung Oh
- Mechanobiology Institute, National University of Singapore, bukit timah, 117411, Singapore
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, 77555, USA
| | - Xuyao Liu
- Mechanobiology Institute, National University of Singapore, bukit timah, 117411, Singapore
| | - Michael P Sheetz
- Mechanobiology Institute, National University of Singapore, bukit timah, 117411, Singapore
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, 77555, USA
| | - Linda J Kenney
- Mechanobiology Institute, National University of Singapore, bukit timah, 117411, Singapore
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, 77555, USA
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Godlee C, Holden DW. Transmembrane substrates of type three secretion system injectisomes. MICROBIOLOGY (READING, ENGLAND) 2023; 169:001292. [PMID: 36748571 PMCID: PMC9993115 DOI: 10.1099/mic.0.001292] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The type three secretion system injectisome of Gram-negative bacterial pathogens injects virulence proteins, called effectors, into host cells. Effectors of mammalian pathogens carry out a range of functions enabling bacterial invasion, replication, immune suppression and transmission. The injectisome secretes two translocon proteins that insert into host cell membranes to form a translocon pore, through which effectors are delivered. A subset of effectors also integrate into infected cell membranes, enabling a unique range of biochemical functions. Both translocon proteins and transmembrane effectors avoid cytoplasmic aggregation and integration into the bacterial inner membrane. Translocated transmembrane effectors locate and integrate into the appropriate host membrane. In this review, we focus on transmembrane translocon proteins and effectors of bacterial pathogens of mammals. We discuss what is known about the mechanisms underlying their membrane integration, as well as the functions conferred by the position of injectisome effectors within membranes.
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Affiliation(s)
- Camilla Godlee
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, Armstrong Road, London SW7 2AZ, UK
- Present address: Department of Infectious Diseases, School of Immunology and Microbial Sciences, King's College London, London, UK
- *Correspondence: Camilla Godlee, ;
| | - David W. Holden
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, Armstrong Road, London SW7 2AZ, UK
- *Correspondence: David W. Holden,
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Godlee C, Cerny O, Liu M, Blundell S, Gallagher AE, Shahin M, Holden DW. The Salmonella transmembrane effector SteD hijacks AP1-mediated vesicular trafficking for delivery to antigen-loading MHCII compartments. PLoS Pathog 2022; 18:e1010252. [PMID: 35622870 PMCID: PMC9182567 DOI: 10.1371/journal.ppat.1010252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Revised: 06/09/2022] [Accepted: 04/27/2022] [Indexed: 12/02/2022] Open
Abstract
SteD is a transmembrane effector of the Salmonella SPI-2 type III secretion system that inhibits T cell activation by reducing the amounts of at least three proteins –major histocompatibility complex II (MHCII), CD86 and CD97 –from the surface of antigen-presenting cells. SteD specifically localises at the trans-Golgi network (TGN) and MHCII compartments; however, the targeting, membrane integration and trafficking of SteD are not understood. Using systematic mutagenesis, we identify distinct regions of SteD that are required for these processes. We show that SteD integrates into membranes of the ER/Golgi through a two-step mechanism of membrane recruitment from the cytoplasm followed by integration. SteD then migrates to and accumulates within the TGN. From here it hijacks the host adaptor protein (AP)1-mediated trafficking pathway from the TGN to MHCII compartments. AP1 binding and post-TGN trafficking require a short sequence in the N-terminal cytoplasmic tail of SteD that resembles the AP1-interacting dileucine sorting signal, but in inverted orientation, suggesting convergent evolution. Salmonella enterica is an intracellular pathogen that causes a range of diseases from gastroenteritis to systemic typhoid fever. Its pathogenesis relies on virulence proteins known as effectors that are delivered into host cells and modulate host cellular processes. The ability of the Salmonella effector SteD to localise within host MHCII compartment membranes is essential for its function in disrupting the adaptive immune response. Here we show that SteD integrates into membranes of the early secretory pathway through a two-step recruitment and integration mechanism. SteD then behaves like a transmembrane cargo protein and hijacks a post-Golgi vesicular trafficking pathway to reach MHCII compartments. This study highlights the sophistication by which bacterial pathogens interact with host cell biology at the molecular level.
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Affiliation(s)
- Camilla Godlee
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom
- * E-mail: (CG); (DWH)
| | - Ondrej Cerny
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom
| | - Mei Liu
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom
| | - Samkeliso Blundell
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom
| | - Alanna E. Gallagher
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom
| | - Meriam Shahin
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom
| | - David W. Holden
- MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom
- * E-mail: (CG); (DWH)
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Krampen L, Malmsheimer S, Grin I, Trunk T, Lührmann A, de Gier JW, Wagner S. Revealing the mechanisms of membrane protein export by virulence-associated bacterial secretion systems. Nat Commun 2018; 9:3467. [PMID: 30150748 PMCID: PMC6110835 DOI: 10.1038/s41467-018-05969-w] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 07/31/2018] [Indexed: 02/08/2023] Open
Abstract
Many bacteria export effector proteins fulfilling their function in membranes of a eukaryotic host. These effector membrane proteins appear to contain signals for two incompatible bacterial secretion pathways in the same protein: a specific export signal, as well as transmembrane segments that one would expect to mediate targeting to the bacterial inner membrane. Here, we show that the transmembrane segments of effector proteins of type III and type IV secretion systems indeed integrate in the membrane as required in the eukaryotic host, but that their hydrophobicity in most instances is just below the threshold required for mediating targeting to the bacterial inner membrane. Furthermore, we show that binding of type III secretion chaperones to both the effector’s chaperone-binding domain and adjacent hydrophobic transmembrane segments also prevents erroneous targeting. These results highlight the evolution of a fine discrimination between targeting pathways that is critical for the virulence of many bacterial pathogens. Many bacteria export effector proteins even when two incompatible signal sequences are present, one which would lead to export and the other to inner membrane targeting. Here the authors show that such proteins feature decreased hydrophobicity or cognate chaperone binding to prevent erroneous targeting.
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Affiliation(s)
- Lea Krampen
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany
| | - Silke Malmsheimer
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany
| | - Iwan Grin
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany
| | - Thomas Trunk
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany.,Section for Genetics and Evolutionary Biology, University of Oslo, Blindernveien 31, 0371, Oslo, Norway
| | - Anja Lührmann
- Institute of Microbiology, University Hospital Erlangen, Wasserturmstr. 3-5, 91054, Erlangen, Germany
| | - Jan-Willem de Gier
- Center for Biomembrane Research, Stockholm University, Svante-Arrhenius väg 16, SE-106 91, Stockholm, Sweden
| | - Samuel Wagner
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany. .,German Center for Infection Research (DZIF), Partner-site Tübingen, Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany.
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Dasanayake D, Richaud M, Cyr N, Caballero-Franco C, Pittroff S, Finn RM, Ausió J, Luo W, Donnenberg MS, Jardim A. The N-terminal amphipathic region of the Escherichia coli type III secretion system protein EspD is required for membrane insertion and function. Mol Microbiol 2011; 81:734-50. [PMID: 21651628 DOI: 10.1111/j.1365-2958.2011.07727.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Enterohemorrhagic Escherichia coli is a causative agent of gastrointestinal and diarrheal diseases. These pathogenic E. coli express a syringe-like protein machine, known as the type III secretion system (T3SS), used for the injection of virulence factors into the cytosol of the host epithelial cell. Breaching the epithelial plasma membrane requires formation of a translocation pore that contains the secreted protein EspD. Here we demonstrate that the N-terminal segment of EspD, encompassing residues 1-171, contains two amphipathic domains spanning residues 24-41 and 66-83, with the latter of these helices being critical for EspD function. Fluorescence and circular dichroism analysis revealed that, in solution, His₆-EspD₁₋₁₇₁ adopts a native disordered structure; however, on binding anionic small unilamellar vesicles composed of phosphatidylserine, His₆-EspD₁₋₁₇₁ undergoes a pH depended conformational change that increases the α-helix content of this protein approximately sevenfold. This change coincides with insertion of the region circumscribing Trp₄₇ into the hydrophobic core of the lipid bilayer. On the HeLa cell plasma membrane, His₆-EspD₁₋₁₇₁ forms a homodimer that is postulated to promote EspD-EspD oligomerization and pore formation. Complementation of ΔespD null mutant bacteria with an espDΔ66-83 gene showed that this protein was secreted but non-functional.
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Affiliation(s)
- Dayal Dasanayake
- Institute of Parasitology and Centre for Host-Parasite Interactions, Macdonald Campus of McGill University, Ste-Anne-de-Bellevue, Québec H9X3V9, Canada
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Comparative analysis of the locus of enterocyte effacement and its flanking regions. Infect Immun 2009; 77:3501-13. [PMID: 19506015 DOI: 10.1128/iai.00090-09] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The attaching-and-effacing (A/E) phenotype mediated by factors derived from the locus of enterocyte effacement (LEE) is a hallmark of clinically important intestinal pathotypes of Escherichia coli, including enteropathogenic (EPEC), atypical EPEC (ATEC), and enterohemorrhagic E. coli strains. Epidemiological studies indicate that the frequency of diarrhea outbreaks caused by ATEC is increasing. Hence, it is of major importance to further characterize putative factors contributing to the pathogenicity of these strains and to gain additional insight into the plasticity and evolutionary aspects of this emerging pathotype. Here, we analyzed the two clinical ATEC isolates B6 (O26:K60) and 9812 (O128:H2) and compared the genetic organizations, flanking regions, and chromosomal insertion loci of their LEE with those of the LEE of other A/E pathogens. Our analysis shows that the core LEE is largely conserved-particularly among genes coding for the type 3 secretion system-whereas genes encoding effector proteins display a higher variability. Chromosomal insertion loci appear to be restricted to selC, pheU, and pheV. In contrast, striking differences were found between the 5'- and 3'-associated flanking regions reflecting the different histories of the various strains and also possibly indicating different lines in evolution.
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Race PR, Solovyova AS, Banfield MJ. Conformation of the EPEC Tir protein in solution: investigating the impact of serine phosphorylation at positions 434/463. Biophys J 2007; 93:586-96. [PMID: 17449672 PMCID: PMC1896257 DOI: 10.1529/biophysj.106.101766] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The translocated intimin receptor (Tir) is a key virulence factor of enteropathogenic Escherichia coli and related bacteria. During infection, Tir is translocated via a type III secretion system into host intestinal epithelial cells, where it inserts into the target cell membrane and acts as a receptor for the bacterial adhesin intimin. The effects of phosphorylation by cAMP-dependent kinase at two serine residues (Ser-434 and Ser-463) within the C-terminal domain of Tir, which may be involved in mediating structural/electrostatic changes in the protein to promote membrane insertion or intermolecular interactions, have previously been investigated. This study has focused on defining the conformation of Tir in solution and assessing any conformational changes associated with serine phosphorylation at positions 434/463. In addition to phosphorylated protein, combinations of Ala (unphosphorylatable) and Asp (phosphate-mimic) mutations of Ser-434 and Ser-463 have been generated, and a range of techniques (sodium dodecyl sulfate polyacrylamide gel electrophoresis, circular dichroism spectroscopy, analytical ultracentrifugation) used to further dissect the structural role and functional implications of changes in residue size/charge at these positions. The results have shown that under physiological NaCl concentrations, Tir is a monomer and adopts a highly elongated state in solution, consistent with a natively unfolded conformation. Despite this, perturbations in the structure in response to buffer conditions and the nature of the residues at positions 434 and 463 are apparent, and may be functionally relevant.
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Affiliation(s)
- Paul R Race
- Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle upon Tyne, United Kingdom
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Rich RL, Myszka DG. Survey of the year 2006 commercial optical biosensor literature. J Mol Recognit 2007; 20:300-66. [DOI: 10.1002/jmr.862] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Campellone KG, Brady MJ, Alamares JG, Rowe DC, Skehan BM, Tipper DJ, Leong JM. Enterohaemorrhagic Escherichia coli Tir requires a C-terminal 12-residue peptide to initiate EspF-mediated actin assembly and harbours N-terminal sequences that influence pedestal length. Cell Microbiol 2006; 8:1488-503. [PMID: 16922867 DOI: 10.1111/j.1462-5822.2006.00728.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Enterohaemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC) both utilize type III secretion systems that translocate the effector protein Tir into the plasma membrane of mammalian cells in order to stimulate localized actin assembly into 'pedestals'. The Tir molecule that EPEC delivers is phosphorylated within its C-terminus on tyrosine-474, and a clustered 12-residue phosphopeptide encompassing this residue initiates an efficient signalling cascade that triggers actin polymerization. In addition to Y474, tyrosine-454 of EPEC Tir is phosphorylated, although inefficiently, and promotes actin polymerization at low levels. In contrast to EPEC Tir, EHEC Tir lacks Y474 and triggers pedestal formation in a phosphotyrosine-independent manner by interacting with an additional effector protein, EspF(U). To identify EHEC Tir sequences that regulate localized actin assembly, we circumvented the strict requirements for type III translocation and directly expressed Tir derivatives in mammalian cells by transfection. Infection of Tir-expressing cells with a Tir-deficient EHEC strain demonstrated that ectopically expressed Tir localizes to the plasma membrane, is modified by mammalian serine-threonine kinases and is fully functional for actin pedestal formation. Removal of portions of the cytoplasmic N-terminus of Tir resulted in the generation of abnormally long pedestals, indicating that this region of EHEC Tir influences pedestal length. In the presence of the entire N-terminal domain, a 12-residue peptide from the C-terminus of EHEC Tir is both necessary and sufficient to recruit EspF(U) and initiate actin pedestal formation. This peptide encompasses the portion of EHEC Tir analogous to the EPEC Tir-Y454 region and is present within the Tir molecules of all pedestal-forming bacteria, suggesting that this sequence harbours a conserved signalling function.
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Affiliation(s)
- Kenneth G Campellone
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, 01655, USA
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