1
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Bailly C, Bedart C, Vergoten G. A molecular docking exploration of the large extracellular loop of tetraspanin CD81 with small molecules. In Silico Pharmacol 2024; 12:24. [PMID: 38584777 PMCID: PMC10997574 DOI: 10.1007/s40203-024-00203-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Accepted: 03/13/2024] [Indexed: 04/09/2024] Open
Abstract
Tetraspanin CD81 is a transmembrane protein used as a co-receptor by different viruses and implicated in some cancer and inflammatory diseases. The design of therapeutic small molecules targeting CD81 lags behind monoclonal antibodies and peptides but different synthetic and natural products binding to CD81 have been identified. We have investigated the interaction between synthetic compounds and CD81, considering both the cholesterol-bound full-length receptor and a truncated protein corresponding to the large extracellular loop (LEL) of the tetraspanin. They represent the closed and open conformations of the protein, respectively. Stable complexes were characterized with bi-aryl compounds (notably the quinolinone-benzothiazole 6) and atypical molecules bearing a 1-amino-boraadamantane scaffold well adapted to interact with CD81 (5a-d). In each case, the mode of binding to CD81 was analyzed, the binding sites identified and the molecular contacts determined. The narrow intra-LEL binding site of CD81 can accommodate the elongated bi-aryl 6 but not a series of isosteric compounds with a bis(bicyclic) scaffold. The bora-adamantane derivatives appeared to bind well to CD81, but essentially to the external surface of the protein loop. The binding selectivity of the compounds was assessed comparing binding to the LEL of tetraspanins CD81, CD9 and Tspan15. A net preference for CD81 over CD9 was evidenced, but the LEL of Tspan15 also provided a suitable binding site for the compounds, notably for the bora-adamantane derivatives. This work provides an aid to the identification and design of tetraspanin-binding small molecules, underlining the distinct behavior of the open and closed conformation of the protein for drug binding. Supplementary Information The online version contains supplementary material available at 10.1007/s40203-024-00203-6.
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Affiliation(s)
- Christian Bailly
- OncoWitan, Scientific Consulting Office, 59290 Lille, Wasquehal, France
- University of Lille, CNRS, Inserm, CHU Lille, UMR9020-U1277, CANTHER, Cancer Heterogeneity Plasticity and Resistance to Therapies, 59000 Lille, France
| | - Corentin Bedart
- University of Lille, Inserm, U1286, INFINITE, Lille Inflammation Research International Center, Institut de Chimie Pharmaceutique Albert Lespagnol (ICPAL)Faculté de Pharmacie, 3 rue du Professeur Laguesse, 59,000 Lille, France
| | - Gérard Vergoten
- University of Lille, Inserm, U1286, INFINITE, Lille Inflammation Research International Center, Institut de Chimie Pharmaceutique Albert Lespagnol (ICPAL)Faculté de Pharmacie, 3 rue du Professeur Laguesse, 59,000 Lille, France
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2
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Broadbent LM, Rothnie AJ, Simms J, Bill RM. Classifying tetraspanins: A universal system for numbering residues and a proposal for naming structural motifs and subfamilies. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184265. [PMID: 38154528 DOI: 10.1016/j.bbamem.2023.184265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 12/06/2023] [Accepted: 12/14/2023] [Indexed: 12/30/2023]
Abstract
All tetraspanins have four transmembrane domains (TMs). The large extracellular loop (LEL) that connects the third and fourth TMs contains multiple secondary structures together with the family's signature Cys-Cys-Gly motif. These intriguing membrane proteins are involved in diverse and incompletely understood cellular processes including cell adhesion, tissue differentiation, immune cell maturation and host-parasite interactions. Here we present a classification system that accurately describes the position of each amino acid within its primary sequence based on both sequence and topological conservation of the TMs and LEL. This builds on the numbering systems that have been used in the G protein-coupled receptor (GPCR) field for nearly three decades and which have aided the understanding of GPCR structure/activity relationships and ligand interactions. The high-resolution structures of the tetraspanins CD81, CD9, CD53 and Tspan15 were used to validate the structural relevance of our new tetraspanin classification system. Modelling of all tetraspanin LELs highlighted flexibility in LEL disulfide bonding across the family and suggests that the structural arrangement of tetraspanin LELs is more complex than previously thought. We therefore propose a new subfamily naming system that addresses this added complexity and facilitates the systematic classification of human tetraspanins, shedding light on all structural motifs within the family. We anticipate that our universal tetraspanin classification system will enable progress in defining how sequence and structure inform function.
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Affiliation(s)
- Luke M Broadbent
- College of Health and Life Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK.
| | - Alice J Rothnie
- College of Health and Life Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK
| | - John Simms
- College of Health and Life Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK
| | - Roslyn M Bill
- College of Health and Life Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK.
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3
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Abu-Saleh N, Kuo CC, Jiang W, Levy R, Levy S. The molecular mechanism of CD81 antibody inhibition of metastasis. Proc Natl Acad Sci U S A 2023; 120:e2305042120. [PMID: 37339209 PMCID: PMC10293848 DOI: 10.1073/pnas.2305042120] [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: 03/29/2023] [Accepted: 05/17/2023] [Indexed: 06/22/2023] Open
Abstract
Metastases are reduced in CD81KO mice. In addition, a unique anti-CD81 antibody, 5A6, inhibits metastasis in vivo and invasion and migration in vitro. Here, we probed the structural components of CD81 required for the antimetastatic activity induced by 5A6. We found that the removal of either cholesterol or the intracellular domains of CD81 did not affect inhibition by the antibody. We show that the uniqueness of 5A6 is due not to increased affinity but rather to its recognition of a specific epitope on the large extracellular loop of CD81. Finally, we present a number of CD81 membrane-associated partners that may play a role in mediating the 5A6 antimetastatic attributes, including integrins and transferrin receptors.
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Affiliation(s)
- Niroz Abu-Saleh
- Division of Oncology, Department of Medicine, Stanford University School of Medicine, Stanford, CA94305
| | - Chiung-Chi Kuo
- Division of Oncology, Department of Medicine, Stanford University School of Medicine, Stanford, CA94305
| | - Wei Jiang
- Division of Oncology, Department of Medicine, Stanford University School of Medicine, Stanford, CA94305
| | - Ronald Levy
- Division of Oncology, Department of Medicine, Stanford University School of Medicine, Stanford, CA94305
| | - Shoshana Levy
- Division of Oncology, Department of Medicine, Stanford University School of Medicine, Stanford, CA94305
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4
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Vermaas JV, Mayne CG, Shinn E, Tajkhorshid E. Assembly and Analysis of Cell-Scale Membrane Envelopes. J Chem Inf Model 2022; 62:602-617. [PMID: 34910495 PMCID: PMC8903035 DOI: 10.1021/acs.jcim.1c01050] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The march toward exascale computing will enable routine molecular simulation of larger and more complex systems, for example, simulation of entire viral particles, on the scale of approximately billions of atoms─a simulation size commensurate with a small bacterial cell. Anticipating the future hardware capabilities that will enable this type of research and paralleling advances in experimental structural biology, efforts are currently underway to develop software tools, procedures, and workflows for constructing cell-scale structures. Herein, we describe our efforts in developing and implementing an efficient and robust workflow for construction of cell-scale membrane envelopes and embedding membrane proteins into them. A new approach for construction of massive membrane structures that are stable during the simulations is built on implementing a subtractive assembly technique coupled with the development of a structure concatenation tool (fastmerge), which eliminates overlapping elements based on volumetric criteria rather than adding successive molecules to the simulation system. Using this approach, we have constructed two "protocells" consisting of MARTINI coarse-grained beads to represent cellular membranes, one the size of a cellular organelle and another the size of a small bacterial cell. The membrane envelopes constructed here remain whole during the molecular dynamics simulations performed and exhibit water flux only through specific proteins, demonstrating the success of our methodology in creating tight cell-like membrane compartments. Extended simulations of these cell-scale structures highlight the propensity for nonspecific interactions between adjacent membrane proteins leading to the formation of protein microclusters on the cell surface, an insight uniquely enabled by the scale of the simulations. We anticipate that the experiences and best practices presented here will form the basis for the next generation of cell-scale models, which will begin to address the addition of soluble proteins, nucleic acids, and small molecules essential to the function of a cell.
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Affiliation(s)
- Josh V. Vermaas
- Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401,;
| | - Christopher G. Mayne
- Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Eric Shinn
- Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Emad Tajkhorshid
- Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801,;
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5
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Quantitative characterization of tetraspanin 8 homointeractions in the plasma membrane. Biochem J 2021; 478:3643-3654. [PMID: 34524408 DOI: 10.1042/bcj20210459] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 09/13/2021] [Accepted: 09/15/2021] [Indexed: 11/17/2022]
Abstract
The spatial distribution of proteins in cell membranes is crucial for signal transduction, cell communication and membrane trafficking. Members of the Tetraspanin family organize functional protein clusters within the plasma membrane into so-called Tetraspanin-enriched microdomains (TEMs). Direct interactions between Tetraspanins are believed to be important for this organization. However, studies thus far have utilized mainly co-immunoprecipitation methods that cannot distinguish between direct and indirect, through common partners, interactions. Here we study Tetraspanin 8 homointeractions in living cells via quantitative fluorescence microscopy. We demonstrate that Tetraspanin 8 exists in a monomer-dimer equilibrium in the plasma membrane. Tetraspanin 8 dimerization is described by a high dissociation constant (Kd = 14 700 ± 1100 Tspan8/µm2), one of the highest dissociation constants measured for membrane proteins in live cells. We propose that this high dissociation constant, and thus the short lifetime of the Tetraspanin 8 dimer, is critical for Tetraspanin 8 functioning as a master regulator of cell signaling.
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6
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Cholesterol plays a decisive role in tetraspanin assemblies during bilayer deformations. Biosystems 2021; 209:104505. [PMID: 34403719 DOI: 10.1016/j.biosystems.2021.104505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2021] [Revised: 07/30/2021] [Accepted: 08/07/2021] [Indexed: 11/22/2022]
Abstract
The tetraspanin family plays key roles in many physiological processes, such as, tumour invasion, cell motility, virus infection, cell attachment and entry. Tetraspanins function as molecular scaffolds organized in microdomains with interesting downstream cellular consequences. However, despite their relevance in human physiology, the precise mechanisms of their various functions remain elusive. In particular, the full-length CD81 tetraspanin has interesting cholesterol-related properties that modulate its activity in cells. In this work, we study the opening transition of CD81 under different conditions. We propose that such conformational change is a collaborative process enhanced by simultaneous interactions between multiple identical CD81 tetraspanins. With molecular dynamics simulations we describe the crucial role of a ternary lipid bilayer with cholesterol in CD81 conformational dynamics, observing two emergent properties: first, clusters of CD81 collectively segregate one tetraspanin while favouring one opening transition, second, cumulative cholesterol sequestering by CD81 tetraspanins inhibits large membrane deformations due to local density variations.
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7
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Palor M, Stejskal L, Mandal P, Lenman A, Alberione MP, Kirui J, Moeller R, Ebner S, Meissner F, Gerold G, Shepherd AJ, Grove J. Cholesterol sensing by CD81 is important for hepatitis C virus entry. J Biol Chem 2020; 295:16931-16948. [PMID: 32900848 PMCID: PMC7863897 DOI: 10.1074/jbc.ra120.014761] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Revised: 08/11/2020] [Indexed: 01/12/2023] Open
Abstract
CD81 plays a central role in a variety of physiological and pathological processes. Recent structural analysis of CD81 indicates that it contains an intramembrane cholesterol-binding pocket and that interaction with cholesterol may regulate a conformational switch in the large extracellular domain of CD81. Therefore, CD81 possesses a potential cholesterol-sensing mechanism; however, its relevance for protein function is thus far unknown. In this study we investigate CD81 cholesterol sensing in the context of its activity as a receptor for hepatitis C virus (HCV). Structure-led mutagenesis of the cholesterol-binding pocket reduced CD81-cholesterol association but had disparate effects on HCV entry, both reducing and enhancing CD81 receptor activity. We reasoned that this could be explained by alterations in the consequences of cholesterol binding. To investigate this further we performed molecular dynamic simulations of CD81 with and without cholesterol; this identified a potential allosteric mechanism by which cholesterol binding regulates the conformation of CD81. To test this, we designed further mutations to force CD81 into either the open (cholesterol-unbound) or closed (cholesterol-bound) conformation. The open mutant of CD81 exhibited reduced HCV receptor activity, whereas the closed mutant enhanced activity. These data are consistent with cholesterol sensing switching CD81 between a receptor active and inactive state. CD81 interactome analysis also suggests that conformational switching may modulate the assembly of CD81-partner protein networks. This work furthers our understanding of the molecular mechanism of CD81 cholesterol sensing, how this relates to HCV entry, and CD81's function as a molecular scaffold; these insights are relevant to CD81's varied roles in both health and disease.
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Affiliation(s)
- Machaela Palor
- Institute of Immunity and Transplantation, Division of Infection and Immunity, University College, London, United Kingdom
| | - Lenka Stejskal
- Institute of Immunity and Transplantation, Division of Infection and Immunity, University College, London, United Kingdom; Institute of Structural and Molecular Biology, Birkbeck College, London, United Kingdom
| | - Piya Mandal
- Institute of Immunity and Transplantation, Division of Infection and Immunity, University College, London, United Kingdom
| | - Annasara Lenman
- Department of Clinical Microbiology, Virology & Wallenberg Centre for Molecular Medicine, Umeå University, Umeå, Sweden; Institute for Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - María Pía Alberione
- Institute for Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - Jared Kirui
- Institute for Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - Rebecca Moeller
- Institute for Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - Stefan Ebner
- Experimental Systems Immunology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Felix Meissner
- Experimental Systems Immunology, Max Planck Institute of Biochemistry, Martinsried, Germany; Institute of Innate Immunity, Department of Systems Immunology and Proteomics, Medical Faculty, University of Bonn, Bonn, Germany
| | - Gisa Gerold
- Department of Clinical Microbiology, Virology & Wallenberg Centre for Molecular Medicine, Umeå University, Umeå, Sweden; Institute for Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany; Department of Physiological Chemistry, University of Veterinary Medicine Hannover, Hannover, Germany
| | - Adrian J Shepherd
- Institute of Structural and Molecular Biology, Birkbeck College, London, United Kingdom
| | - Joe Grove
- Institute of Immunity and Transplantation, Division of Infection and Immunity, University College, London, United Kingdom.
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8
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Oosterheert W, Xenaki KT, Neviani V, Pos W, Doulkeridou S, Manshande J, Pearce NM, Kroon-Batenburg LM, Lutz M, van Bergen En Henegouwen PM, Gros P. Implications for tetraspanin-enriched microdomain assembly based on structures of CD9 with EWI-F. Life Sci Alliance 2020; 3:3/11/e202000883. [PMID: 32958604 PMCID: PMC7536822 DOI: 10.26508/lsa.202000883] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Revised: 09/04/2020] [Accepted: 09/04/2020] [Indexed: 01/17/2023] Open
Abstract
Crystal and single-particle cryo-EM structures reveal how the tetraspanin CD9 interacts with its prototypical partner EWI-F and provide a new concatenation model for the assembly of tetraspanin-enriched microdomains. Tetraspanins are eukaryotic membrane proteins that contribute to a variety of signaling processes by organizing partner-receptor molecules in the plasma membrane. How tetraspanins bind and cluster partner receptors into tetraspanin-enriched microdomains is unknown. Here, we present crystal structures of the large extracellular loop of CD9 bound to nanobodies 4C8 and 4E8 and, the cryo-EM structure of 4C8-bound CD9 in complex with its partner EWI-F. CD9–EWI-F displays a tetrameric arrangement with two central EWI-F molecules, dimerized through their ectodomains, and two CD9 molecules, one bound to each EWI-F transmembrane helix through CD9-helices h3 and h4. In the crystal structures, nanobodies 4C8 and 4E8 bind CD9 at loops C and D, which is in agreement with the 4C8 conformation in the CD9–EWI-F complex. The complex varies from nearly twofold symmetric (with the two CD9 copies nearly anti-parallel) to ca. 50° bent arrangements. This flexible arrangement of CD9–EWI-F with potential CD9 homo-dimerization at either end provides a “concatenation model” for forming short linear or circular assemblies, which may explain the occurrence of tetraspanin-enriched microdomains.
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Affiliation(s)
- Wout Oosterheert
- Department of Chemistry, Crystal and Structural Chemistry, Bijvoet Centre for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Katerina T Xenaki
- Department of Biology, Cell Biology, Neurobiology and Biophysics, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Viviana Neviani
- Department of Chemistry, Crystal and Structural Chemistry, Bijvoet Centre for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Wouter Pos
- uniQure Biopharma, Amsterdam, The Netherlands
| | - Sofia Doulkeridou
- Department of Biology, Cell Biology, Neurobiology and Biophysics, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Jip Manshande
- Department of Chemistry, Crystal and Structural Chemistry, Bijvoet Centre for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Nicholas M Pearce
- Department of Chemistry, Crystal and Structural Chemistry, Bijvoet Centre for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Loes Mj Kroon-Batenburg
- Department of Chemistry, Crystal and Structural Chemistry, Bijvoet Centre for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Martin Lutz
- Department of Chemistry, Crystal and Structural Chemistry, Bijvoet Centre for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Paul Mp van Bergen En Henegouwen
- Department of Biology, Cell Biology, Neurobiology and Biophysics, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Piet Gros
- Department of Chemistry, Crystal and Structural Chemistry, Bijvoet Centre for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, The Netherlands
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9
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Susa KJ, Seegar TCM, Blacklow SC, Kruse AC. A dynamic interaction between CD19 and the tetraspanin CD81 controls B cell co-receptor trafficking. eLife 2020; 9:e52337. [PMID: 32338599 PMCID: PMC7228769 DOI: 10.7554/elife.52337] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 04/26/2020] [Indexed: 12/20/2022] Open
Abstract
CD81 and its binding partner CD19 are core subunits of the B cell co-receptor complex. While CD19 belongs to the extensively studied Ig superfamily, CD81 belongs to a poorly understood family of four-pass transmembrane proteins called tetraspanins. Tetraspanins play important physiological roles by controlling protein trafficking and other processes. Here, we show that CD81 relies on its ectodomain to traffic CD19 to the cell surface. Moreover, the anti-CD81 antibody 5A6, which binds selectively to activated B cells, recognizes a conformational epitope on CD81 that is masked when CD81 is bound to CD19. Mutations of CD81 in this interface suppress its CD19 export activity. These data indicate that the CD81 - CD19 interaction is dynamically regulated upon B cell activation and this dynamism can be exploited to regulate B cell function. These results are not only valuable for understanding B cell biology, but also have important implications for understanding tetraspanin function generally.
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Affiliation(s)
- Katherine J Susa
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical SchoolBostonUnited States
| | - Tom CM Seegar
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical SchoolBostonUnited States
| | - Stephen C Blacklow
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical SchoolBostonUnited States
- Dana Farber Cancer Institute, Department of Cancer BiologyBostonUnited States
| | - Andrew C Kruse
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical SchoolBostonUnited States
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10
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Classes of non-conventional tetraspanins defined by alternative splicing. Sci Rep 2019; 9:14075. [PMID: 31575878 PMCID: PMC6773723 DOI: 10.1038/s41598-019-50267-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 09/10/2019] [Indexed: 11/08/2022] Open
Abstract
Tetraspanins emerge as a family of membrane proteins mediating an exceptional broad diversity of functions. The naming refers to their four transmembrane segments, which define the tetraspanins' typical membrane topology. In this study, we analyzed alternative splicing of tetraspanins. Besides isoforms with four transmembrane segments, most mRNA sequences are coding for isoforms with one, two or three transmembrane segments, representing structurally mono-, di- and trispanins. Moreover, alternative splicing may alter transmembrane topology, delete parts of the large extracellular loop, or generate alternative N- or C-termini. As a result, we define structure-based classes of non-conventional tetraspanins. The increase in gene products by alternative splicing is associated with an unexpected high structural variability of tetraspanins. We speculate that non-conventional tetraspanins have roles in regulating ER exit and modulating tetraspanin-enriched microdomain function.
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11
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Abstract
Cancer-initiating cells (CIC) are the driving force in tumor progression. There is strong evidence that CIC fulfill this task via exosomes (TEX), which modulate and reprogram stroma, nontransformed cells, and non-CIC. Characterization of CIC, besides others, builds on expression of CIC markers, many of which are known as metastasis-associated molecules. We here discuss that the linkage between CIC/CIC-TEX and metastasis-associated molecules is not fortuitously, but relies on the contribution of these markers to TEX biogenesis including loading and TEX target interactions. In addition, CIC markers contribute to TEX binding- and uptake-promoted activation of signaling cascades, transcription initiation, and translational control. Our point of view will be outlined for pancreas and colon CIC highly expressing CD44v6, Tspan8, EPCAM, claudin7, and LGR5, which distinctly but coordinately contribute to tumor progression. Despite overwhelming progress in unraveling the metastatic cascade and the multiple tasks taken over by CIC-TEX, there remains a considerable gap in linking CIC biomarkers, TEX, and TEX-initiated target modulation with metastasis. We will try to outline possible bridges, which could allow depicting pathways for new and expectedly powerful therapeutic interference with tumor progression.
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Affiliation(s)
- Zhe Wang
- Department of Oncology, The First Affiliated Hospital of Guangdong Pharmaceutical University, Guangzhou, China.
| | - Margot Zöller
- Department of Oncology, The First Affiliated Hospital of Guangdong Pharmaceutical University, Guangzhou, China.
- Pancreas Section, University Hospital of Surgery, Heidelberg, Germany.
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12
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Marrink SJ, Corradi V, Souza PC, Ingólfsson HI, Tieleman DP, Sansom MS. Computational Modeling of Realistic Cell Membranes. Chem Rev 2019; 119:6184-6226. [PMID: 30623647 PMCID: PMC6509646 DOI: 10.1021/acs.chemrev.8b00460] [Citation(s) in RCA: 410] [Impact Index Per Article: 82.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Indexed: 12/15/2022]
Abstract
Cell membranes contain a large variety of lipid types and are crowded with proteins, endowing them with the plasticity needed to fulfill their key roles in cell functioning. The compositional complexity of cellular membranes gives rise to a heterogeneous lateral organization, which is still poorly understood. Computational models, in particular molecular dynamics simulations and related techniques, have provided important insight into the organizational principles of cell membranes over the past decades. Now, we are witnessing a transition from simulations of simpler membrane models to multicomponent systems, culminating in realistic models of an increasing variety of cell types and organelles. Here, we review the state of the art in the field of realistic membrane simulations and discuss the current limitations and challenges ahead.
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Affiliation(s)
- Siewert J. Marrink
- Groningen
Biomolecular Sciences and Biotechnology Institute & Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Valentina Corradi
- Centre
for Molecular Simulation and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
| | - Paulo C.T. Souza
- Groningen
Biomolecular Sciences and Biotechnology Institute & Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Helgi I. Ingólfsson
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
| | - D. Peter Tieleman
- Centre
for Molecular Simulation and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
| | - Mark S.P. Sansom
- Department
of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K.
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13
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Mu W, Wang Z, Zöller M. Ping-Pong-Tumor and Host in Pancreatic Cancer Progression. Front Oncol 2019; 9:1359. [PMID: 31921628 PMCID: PMC6927459 DOI: 10.3389/fonc.2019.01359] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 11/18/2019] [Indexed: 12/12/2022] Open
Abstract
Metastasis is the main cause of high pancreatic cancer (PaCa) mortality and trials dampening PaCa mortality rates are not satisfying. Tumor progression is driven by the crosstalk between tumor cells, predominantly cancer-initiating cells (CIC), and surrounding cells and tissues as well as distant organs, where tumor-derived extracellular vesicles (TEX) are of major importance. A strong stroma reaction, recruitment of immunosuppressive leukocytes, perineural invasion, and early spread toward the peritoneal cavity, liver, and lung are shared with several epithelial cell-derived cancer, but are most prominent in PaCa. Here, we report on the state of knowledge on the PaCIC markers Tspan8, alpha6beta4, CD44v6, CXCR4, LRP5/6, LRG5, claudin7, EpCAM, and CD133, which all, but at different steps, are engaged in the metastatic cascade, frequently via PaCIC-TEX. This includes the contribution of PaCIC markers to TEX biogenesis, targeting, and uptake. We then discuss PaCa-selective features, where feedback loops between stromal elements and tumor cells, including distorted transcription, signal transduction, and metabolic shifts, establish vicious circles. For the latter particularly pancreatic stellate cells (PSC) are responsible, furnishing PaCa to cope with poor angiogenesis-promoted hypoxia by metabolic shifts and direct nutrient transfer via vesicles. Furthermore, nerves including Schwann cells deliver a large range of tumor cell attracting factors and Schwann cells additionally support PaCa cell survival by signaling receptor binding. PSC, tumor-associated macrophages, and components of the dysplastic stroma contribute to perineural invasion with signaling pathway activation including the cholinergic system. Last, PaCa aggressiveness is strongly assisted by the immune system. Although rich in immune cells, only immunosuppressive cells and factors are recovered in proximity to tumor cells and hamper effector immune cells entering the tumor stroma. Besides a paucity of immunostimulatory factors and receptors, immunosuppressive cytokines, myeloid-derived suppressor cells, regulatory T-cells, and M2 macrophages as well as PSC actively inhibit effector cell activation. This accounts for NK cells of the non-adaptive and cytotoxic T-cells of the adaptive immune system. We anticipate further deciphering the molecular background of these recently unraveled intermingled phenomena may turn most lethal PaCa into a curatively treatable disease.
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Affiliation(s)
- Wei Mu
- School of Public Health, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- *Correspondence: Wei Mu
| | - Zhe Wang
- Department of Oncology, The First Affiliated Hospital of Guangdong, Pharmaceutical University, Guangzhou, China
| | - Margot Zöller
- Department of Oncology, The First Affiliated Hospital of Guangdong, Pharmaceutical University, Guangzhou, China
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14
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Vogt S, Stadlmayr G, Stadlbauer K, Sádio F, Andorfer P, Grillari J, Rüker F, Wozniak-Knopp G. Stabilization of the CD81 Large Extracellular Loop with De Novo Disulfide Bonds Improves Its Amenability for Peptide Grafting. Pharmaceutics 2018; 10:E138. [PMID: 30150531 PMCID: PMC6160918 DOI: 10.3390/pharmaceutics10030138] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Revised: 08/21/2018] [Accepted: 08/22/2018] [Indexed: 11/16/2022] Open
Abstract
Tetraspan proteins are significantly enriched in the membranes of exosomal vesicles (EVs) and their extracellular domains are attractive targets for engineering towards specific antigen recognition units. To enhance the tolerance of a tetraspanin fold to modification, we achieved significant thermal stabilization of the human CD81 large extracellular loop (hCD81 LEL) via de novo disulfide bonds. The best mutants were shown to exhibit a positive shift in the melting temperature (Tm) of up to 25 °C. The combination of two most potent disulfide bonds connecting different strands of the protein resulted in a mutant with a Tm of 109 °C, 43 °C over the Tm of the wild-type hCD81 LEL. A peptide sequence binding to the human transferrin receptor (hTfr) was engrafted into the D-segment of the hCD81 LEL, resulting in a mutant that still exhibited a compact fold. Grafting of the same peptide sequence between helices A and B resulted in a molecule with an aberrant profile in size exclusion chromatography (SEC), which could be improved by a de novo cysteine bond connecting both helices. Both peptide-grafted proteins showed an enhanced internalization into the cell line SK-BR3, which strongly overexpresses hTfr. In summary, the tetraspan LEL fold could be stabilized to enhance its amenability for engineering into a more versatile protein scaffold.
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Affiliation(s)
- Stefan Vogt
- acib GmbH (Austrian Centre of Industrial Biotechnology), Petersgasse 14, A-8010 Graz, Austria.
| | - Gerhard Stadlmayr
- Christian Doppler Laboratory for Innovative Immunotherapeutics, Department of Biotechnology, University of Natural Resources and Life Sciences (BOKU), Vienna, Muthgasse 18, 1190 Vienna, Austria.
| | - Katharina Stadlbauer
- Christian Doppler Laboratory for Innovative Immunotherapeutics, Department of Biotechnology, University of Natural Resources and Life Sciences (BOKU), Vienna, Muthgasse 18, 1190 Vienna, Austria.
| | - Flávio Sádio
- Christian Doppler Laboratory for Innovative Immunotherapeutics, Department of Biotechnology, University of Natural Resources and Life Sciences (BOKU), Vienna, Muthgasse 18, 1190 Vienna, Austria.
| | - Peter Andorfer
- Christian Doppler Laboratory for Innovative Immunotherapeutics, Department of Biotechnology, University of Natural Resources and Life Sciences (BOKU), Vienna, Muthgasse 18, 1190 Vienna, Austria.
| | - Johannes Grillari
- Christian Doppler Laboratory for Biotechnology of Skin Aging, Department of Biotechnology, University of Natural Resources and Life Sciences (BOKU), Vienna, Muthgasse 18, 1190 Vienna, Austria;.
- Evercyte GmbH, Muthgasse 18, 1190 Wien, Austria.
| | - Florian Rüker
- acib GmbH (Austrian Centre of Industrial Biotechnology), Petersgasse 14, A-8010 Graz, Austria.
- Christian Doppler Laboratory for Innovative Immunotherapeutics, Department of Biotechnology, University of Natural Resources and Life Sciences (BOKU), Vienna, Muthgasse 18, 1190 Vienna, Austria.
| | - Gordana Wozniak-Knopp
- acib GmbH (Austrian Centre of Industrial Biotechnology), Petersgasse 14, A-8010 Graz, Austria.
- Christian Doppler Laboratory for Innovative Immunotherapeutics, Department of Biotechnology, University of Natural Resources and Life Sciences (BOKU), Vienna, Muthgasse 18, 1190 Vienna, Austria.
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15
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Florin L, Lang T. Tetraspanin Assemblies in Virus Infection. Front Immunol 2018; 9:1140. [PMID: 29887866 PMCID: PMC5981178 DOI: 10.3389/fimmu.2018.01140] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 05/07/2018] [Indexed: 12/23/2022] Open
Abstract
Tetraspanins (Tspans) are a family of four-span transmembrane proteins, known as plasma membrane “master organizers.” They form Tspan-enriched microdomains (TEMs or TERMs) through lateral association with one another and other membrane proteins. If multiple microdomains associate with each other, larger platforms can form. For infection, viruses interact with multiple cell surface components, including receptors, activating proteases, and signaling molecules. It appears that Tspans, such as CD151, CD82, CD81, CD63, CD9, Tspan9, and Tspan7, coordinate these associations by concentrating the interacting partners into Tspan platforms. In addition to mediating viral attachment and entry, these platforms may also be involved in intracellular trafficking of internalized viruses and assist in defining virus assembly and exit sites. In conclusion, Tspans play a role in viral infection at different stages of the virus replication cycle. The present review highlights recently published data on this topic, with a focus on events at the plasma membrane. In light of these findings, we propose a model for how Tspan interactions may organize cofactors for viral infection into distinct molecular platforms.
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Affiliation(s)
- Luise Florin
- Department of Medical Microbiology and Hygiene, University Medical Center of the Johannes Gutenberg University, Mainz, Germany
| | - Thorsten Lang
- Department of Membrane Biochemistry, Life & Medical Sciences Institute, University of Bonn, Bonn, Germany
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16
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Grove J, Hu K, Farquhar MJ, Goodall M, Walker L, Jamshad M, Drummer HE, Bill RM, Balfe P, McKeating JA. A new panel of epitope mapped monoclonal antibodies recognising the prototypical tetraspanin CD81. Wellcome Open Res 2017; 2:82. [PMID: 29090272 PMCID: PMC5657224 DOI: 10.12688/wellcomeopenres.12058.1] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/16/2017] [Indexed: 12/26/2022] Open
Abstract
Background: Tetraspanins are small transmembrane proteins, found in all higher eukaryotes, that compartmentalize cellular membranes through interactions with partner proteins. CD81 is a prototypical tetraspanin and contributes to numerous physiological and pathological processes, including acting as a critical entry receptor for hepatitis C virus (HCV). Antibody engagement of tetraspanins can induce a variety of effects, including actin cytoskeletal rearrangements, activation of MAPK-ERK signaling and cell migration. However, the epitope specificity of most anti-tetraspanin antibodies is not known, limiting mechanistic interpretation of these studies. Methods: We generated a panel of monoclonal antibodies (mAbs) specific for CD81 second extracellular domain (EC2) and performed detailed epitope mapping with a panel of CD81 mutants. All mAbs were screened for their ability to inhibit HCV infection and E2-CD81 association. Nanoscale distribution of cell surface CD81 was investigated by scanning electron microscopy. Results: The antibodies were classified in two epitope groups targeting opposing sides of EC2. We observed a wide range of anti-HCV potencies that were independent of their epitope grouping, but associated with their relative affinity for cell-surface expressed CD81. Scanning electron microscopy identified at least two populations of CD81; monodisperse and higher-order assemblies, consistent with tetraspanin-enriched microdomains. Conclusions: These novel antibodies provide well-characterised tools to investigate CD81 function, including HCV entry, and have the potential to provide insights into tetraspanin biology in general.
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Affiliation(s)
- Joe Grove
- Institute of Immunity and Transplantation, Division of Infection and Immunity, , University College London, London, NW3 2PF, UK
| | - Ke Hu
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, B15 2TT, UK
| | - Michelle J. Farquhar
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, B15 2TT, UK
| | - Margaret Goodall
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, B15 2TT, UK
| | - Lucas Walker
- Institute of Immunity and Transplantation, Division of Infection and Immunity, , University College London, London, NW3 2PF, UK
| | - Mohammed Jamshad
- Institute for Microbiology and Infection, School of Biosciences, University of Birmingham, Birmingham, B15 2TT, UK
| | - Heidi E. Drummer
- Centre for Biomedical Resear, Burnet Institute, Melbourne, VIC, 3004, Australia
| | - Roslyn M. Bill
- School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK
| | - Peter Balfe
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, B15 2TT, UK
| | - Jane A. McKeating
- Nuffield Department of Medicine, University of Oxford, Oxford, OX3 7BN, UK
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17
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Molecular interactions shaping the tetraspanin web. Biochem Soc Trans 2017; 45:741-750. [PMID: 28620035 DOI: 10.1042/bst20160284] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 03/14/2017] [Accepted: 03/15/2017] [Indexed: 12/31/2022]
Abstract
To facilitate the myriad of different (signaling) processes that take place at the plasma membrane, cells depend on a high degree of membrane protein organization. Important mediators of this organization are tetraspanin proteins. Tetraspanins interact laterally among themselves and with partner proteins to control the spatial organization of membrane proteins in large networks called the tetraspanin web. The molecular interactions underlying the formation of the tetraspanin web were hitherto mainly described based on their resistance to different detergents, a classification which does not necessarily correlate with functionality in the living cell. To look at these interactions from a more physiological point of view, this review discusses tetraspanin interactions based on their function in the tetraspanin web: (1) intramolecular interactions supporting tetraspanin structure, (2) tetraspanin-tetraspanin interactions supporting web formation, (3) tetraspanin-partner interactions adding functional partners to the web and (4) cytosolic tetraspanin interactions regulating intracellular signaling. The recent publication of the first full-length tetraspanin crystal structure sheds new light on both the intra- and intermolecular tetraspanin interactions that shape the tetraspanin web. Furthermore, recent molecular dynamic modeling studies indicate that the binding strength between tetraspanins and between tetraspanins and their partners is the complex sum of both promiscuous and specific interactions. A deeper insight into this complex mixture of interactions is essential to our fundamental understanding of the tetraspanin web and its dynamics which constitute a basic building block of the cell surface.
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18
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Grigorov B, Molle J, Rubinstein E, Zoulim F, Bartosch B. CD81 large extracellular loop-containing fusion proteins with a dominant negative effect on HCV cell spread and replication. J Gen Virol 2017; 98:1646-1657. [PMID: 28721844 DOI: 10.1099/jgv.0.000850] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The roles of CD81 in the hepatitis C virus (HCV) life cycle are multiple but remain ill characterized. CD81 is known to interact with the HCV glycoproteins as an attachment factor. It also has an important role in the post-attachment entry process. Its interaction with claudin-1, for example, is vital for viral uptake and trafficking. Furthermore, CD81 and its role in membrane organization and trafficking are thought to play a pivotal role in HCV replication. Some of these functions are particularly limited to human CD81; others can be substituted with CD81 molecules from other species. However, with the exception of the large extracellular loop sequence, the structure-function analysis of CD81 in the HCV infectious cycle remains ill characterized. We describe here the fusion molecules between the large extracellular loops of human or mouse CD81 and lipid-raft-associated or unassociated GPI anchors. These fusion molecules have strong antiviral activity in a dominant negative fashion, independent of membrane raft association. Their expression in the hepatoma cell line Huh7.5 blocks HCV uptake, transmission and replication. These molecules will be useful to decipher the various roles of CD81 in the HCV life cycle and transmission in more detail.
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Affiliation(s)
- Boyan Grigorov
- Univ Lyon, Université Claude Bernard Lyon 1, INSERM 1052, CNRS 5286, Centre Léon Bérard, Centre de recherche en cancérologie de Lyon, 69434 Lyon, France
| | - Jennifer Molle
- Univ Lyon, Université Claude Bernard Lyon 1, INSERM 1052, CNRS 5286, Centre Léon Bérard, Centre de recherche en cancérologie de Lyon, 69434 Lyon, France
| | | | - Fabien Zoulim
- Univ Lyon, Université Claude Bernard Lyon 1, INSERM 1052, CNRS 5286, Centre Léon Bérard, Centre de recherche en cancérologie de Lyon, 69434 Lyon, France.,Hospices Civils de Lyon (HCL), Lyon, France
| | - Birke Bartosch
- Univ Lyon, Université Claude Bernard Lyon 1, INSERM 1052, CNRS 5286, Centre Léon Bérard, Centre de recherche en cancérologie de Lyon, 69434 Lyon, France
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19
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Reducing isoform complexity of human tetraspanins by optimized expression in Dictyostelium discoideum enables high-throughput functional read-out. Protein Expr Purif 2017; 135:8-15. [DOI: 10.1016/j.pep.2017.04.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 04/18/2017] [Accepted: 04/20/2017] [Indexed: 11/21/2022]
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20
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Tetraspanins in infections by human cytomegalo- and papillomaviruses. Biochem Soc Trans 2017; 45:489-497. [PMID: 28408489 DOI: 10.1042/bst20160295] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 02/15/2017] [Accepted: 02/16/2017] [Indexed: 12/30/2022]
Abstract
Members of the tetraspanin family have been identified as essential cellular membrane proteins in infectious diseases by nearly all types of pathogens. The present review highlights recently published data on the role of tetraspanin CD151, CD81, and CD63 and their interaction partners in host cell entry by human cytomegalo- and human papillomaviruses. Moreover, we discuss a model for tetraspanin assembly into trafficking platforms at the plasma membrane. These platforms might persist during intracellular viral trafficking.
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21
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Homsi Y, Lang T. The specificity of homomeric clustering of CD81 is mediated by its δ-loop. FEBS Open Bio 2017; 7:274-283. [PMID: 28174692 PMCID: PMC5292664 DOI: 10.1002/2211-5463.12187] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 12/07/2016] [Accepted: 12/14/2016] [Indexed: 01/26/2023] Open
Abstract
Tetraspanins are cell membrane‐scaffolding proteins interacting with one another and a repertoire of interaction partners. Through these interactions, they form extended molecular networks as tetraspanin webs or tetraspanin‐enriched microdomains. Microscopic data suggest that these networks contain tetraspanin clusters, with poor overlap between clusters formed by different tetraspanins. Here, we investigate the possibility of targeting tetraspanins CD9 or CD151 to clusters formed by the tetraspanin CD81. We find that the δ‐loop from the large extracellular domain of CD81 is sufficient for targeting of CD9/CD151 to CD81 clusters. Moreover, in a pull‐down assay, CD9 coprecipitates more CD81 when it carries the CD81 δ‐loop. In conclusion, the information for forming homomeric CD81 clusters is encoded in the δ‐loop.
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Affiliation(s)
- Yahya Homsi
- Membrane Biochemistry Life & Medical Sciences (LIMES) Institute University of Bonn Germany
| | - Thorsten Lang
- Membrane Biochemistry Life & Medical Sciences (LIMES) Institute University of Bonn Germany
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