1
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Umthong S, Timilsina U, D’Angelo M, Stavrou S. Determining the antiviral mechanism of MARCH2. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.18.558306. [PMID: 37786722 PMCID: PMC10541590 DOI: 10.1101/2023.09.18.558306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
Membrane-associated RING-CH (MARCH) 2 protein is a member of the MARCH protein family of RING-CH finger E3 ubiquitin ligases that have important functions in regulating the levels of proteins found on the cell surface. MARCH1, 2 and 8 inhibit HIV-1 infection by preventing the incorporation of the envelope glycoproteins in nascent virions. However, a better understanding on the mechanism utilized by MARCH proteins to restrict HIV-1 is needed. In this report, we identify an amino acid in human MARCH2, that is absent in mouse MARCH2, critical for its antiretroviral function. Moreover, we map the domains of human MARCH2 critical for restricting as well as binding to the HIV-1 envelope glycoproteins. Our findings reveal important new aspects of the antiviral mechanism utilized by human MARCH2 to restrict HIV-1 that have potential implications to all MARCH proteins with antiviral functions.
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Affiliation(s)
- Supawadee Umthong
- Department of Microbiology and Immunology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, United States
- Department of Biochemistry and Microbiology, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand
| | - Uddhav Timilsina
- Department of Microbiology and Immunology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, United States
| | - Mary D’Angelo
- Department of Microbiology and Immunology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, United States
| | - Spyridon Stavrou
- Department of Microbiology and Immunology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, United States
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2
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Caillat C, Guilligay D, Torralba J, Friedrich N, Nieva JL, Trkola A, Chipot CJ, Dehez FL, Weissenhorn W. Structure of HIV-1 gp41 with its membrane anchors targeted by neutralizing antibodies. eLife 2021; 10:65005. [PMID: 33871352 PMCID: PMC8084527 DOI: 10.7554/elife.65005] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Accepted: 04/18/2021] [Indexed: 12/19/2022] Open
Abstract
The HIV-1 gp120/gp41 trimer undergoes a series of conformational changes in order to catalyze gp41-induced fusion of viral and cellular membranes. Here, we present the crystal structure of gp41 locked in a fusion intermediate state by an MPER-specific neutralizing antibody. The structure illustrates the conformational plasticity of the six membrane anchors arranged asymmetrically with the fusion peptides and the transmembrane regions pointing into different directions. Hinge regions located adjacent to the fusion peptide and the transmembrane region facilitate the conformational flexibility that allows high-affinity binding of broadly neutralizing anti-MPER antibodies. Molecular dynamics simulation of the MPER Ab-stabilized gp41 conformation reveals a possible transition pathway into the final post-fusion conformation with the central fusion peptides forming a hydrophobic core with flanking transmembrane regions. This suggests that MPER-specific broadly neutralizing antibodies can block final steps of refolding of the fusion peptide and the transmembrane region, which is required for completing membrane fusion.
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Affiliation(s)
- Christophe Caillat
- Univ. Grenoble Alpes, CEA, CNRS, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Delphine Guilligay
- Univ. Grenoble Alpes, CEA, CNRS, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Johana Torralba
- Instituto Biofisika (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), Bilbao, Spain
| | - Nikolas Friedrich
- Institute of Medical Virology, University of Zurich, Zurich, Switzerland
| | - Jose L Nieva
- Instituto Biofisika (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), Bilbao, Spain
| | - Alexandra Trkola
- Institute of Medical Virology, University of Zurich, Zurich, Switzerland
| | - Christophe J Chipot
- Laboratoire de Physique et Chimie Théoriques (LPCT), University of Lorraine, Vandoeuvre-lès-Nancy, France.,Laboratoire International Associé, CNRS and University of Illinois at Urbana-Champaign, Vandoeuvre-lès-Nancy, France.,Department of Physics, University of Illinois at Urbana-Champaign, Urbana, United States
| | - François L Dehez
- Laboratoire de Physique et Chimie Théoriques (LPCT), University of Lorraine, Vandoeuvre-lès-Nancy, France.,Laboratoire International Associé, CNRS and University of Illinois at Urbana-Champaign, Vandoeuvre-lès-Nancy, France
| | - Winfried Weissenhorn
- Univ. Grenoble Alpes, CEA, CNRS, Institut de Biologie Structurale (IBS), Grenoble, France
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3
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Aisenbrey C, Rifi O, Bechinger B. Structure, membrane topology and influence of cholesterol of the membrane proximal region: transmembrane helical anchor sequence of gp41 from HIV. Sci Rep 2020; 10:22278. [PMID: 33335248 PMCID: PMC7746737 DOI: 10.1038/s41598-020-79327-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 11/30/2020] [Indexed: 11/13/2022] Open
Abstract
During the first steps of HIV infection the Env subunit gp41 is thought to establish contact between the membranes and to be the main driver of fusion. Here we investigated in liquid crystalline membranes the structure and cholesterol recognition of constructs made of a gp41 external region carrying a cholesterol recognition amino acid consensus (CRAC) motif and a hydrophobic membrane anchoring sequence. CD- und ATR-FTIR spectroscopies indicate that the constructs adopt a high degree of helical secondary structure in membrane environments. Furthermore, 15N and 2H solid-state NMR spectra of gp41 polypeptides reconstituted into uniaxially oriented bilayers agree with the CRAC domain being an extension of the transmembrane helix. Upon addition of cholesterol the CRAC NMR spectra remain largely unaffected when being associated with the native gp41 transmembrane sequence but its topology changes when anchored in the membrane by a hydrophobic model sequence. The 2H solid-state NMR spectra of deuterated cholesterol are indicative of a stronger influence of the model sequence on this lipid when compared to the native gp41 sequence. These observations are suggestive of a strong coupling between the transmembrane and the membrane proximal region of gp41 possibly enforced by oligomerization of the transmembrane helical region.
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Affiliation(s)
- Christopher Aisenbrey
- Institut de chimie de Strasbourg, UMR7177, University of Strasbourg/CNRS, 4, Rue Blaise Pascal, 67070, Strasbourg, France
| | - Omar Rifi
- Institut de chimie de Strasbourg, UMR7177, University of Strasbourg/CNRS, 4, Rue Blaise Pascal, 67070, Strasbourg, France
| | - Burkhard Bechinger
- Institut de chimie de Strasbourg, UMR7177, University of Strasbourg/CNRS, 4, Rue Blaise Pascal, 67070, Strasbourg, France.
- Institut Universitaire de France, Paris, France.
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4
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Barrett CT, Dutch RE. Viral Membrane Fusion and the Transmembrane Domain. Viruses 2020; 12:v12070693. [PMID: 32604992 PMCID: PMC7412173 DOI: 10.3390/v12070693] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 06/24/2020] [Accepted: 06/25/2020] [Indexed: 01/05/2023] Open
Abstract
Initiation of host cell infection by an enveloped virus requires a viral-to-host cell membrane fusion event. This event is mediated by at least one viral transmembrane glycoprotein, termed the fusion protein, which is a key therapeutic target. Viral fusion proteins have been studied for decades, and numerous critical insights into their function have been elucidated. However, the transmembrane region remains one of the most poorly understood facets of these proteins. In the past ten years, the field has made significant advances in understanding the role of the membrane-spanning region of viral fusion proteins. We summarize developments made in the past decade that have contributed to the understanding of the transmembrane region of viral fusion proteins, highlighting not only their critical role in the membrane fusion process, but further demonstrating their involvement in several aspects of the viral lifecycle.
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5
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Pinto D, Fenwick C, Caillat C, Silacci C, Guseva S, Dehez F, Chipot C, Barbieri S, Minola A, Jarrossay D, Tomaras GD, Shen X, Riva A, Tarkowski M, Schwartz O, Bruel T, Dufloo J, Seaman MS, Montefiori DC, Lanzavecchia A, Corti D, Pantaleo G, Weissenhorn W. Structural Basis for Broad HIV-1 Neutralization by the MPER-Specific Human Broadly Neutralizing Antibody LN01. Cell Host Microbe 2019; 26:623-637.e8. [PMID: 31653484 PMCID: PMC6854463 DOI: 10.1016/j.chom.2019.09.016] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 08/29/2019] [Accepted: 09/27/2019] [Indexed: 11/24/2022]
Abstract
Potent and broadly neutralizing antibodies (bnAbs) are the hallmark of HIV-1 protection by vaccination. The membrane-proximal external region (MPER) of the HIV-1 gp41 fusion protein is targeted by the most broadly reactive HIV-1 neutralizing antibodies. Here, we examine the structural and molecular mechansims of neutralization by anti-MPER bnAb, LN01, which was isolated from lymph-node-derived germinal center B cells of an elite controller and exhibits broad neutralization breadth. LN01 engages both MPER and the transmembrane (TM) region, which together form a continuous helix in complex with LN01. The tilted TM orientation allows LN01 to interact simultaneously with the peptidic component of the MPER epitope and membrane via two specific lipid binding sites of the antibody paratope. Although LN01 carries a high load of somatic mutations, most key residues interacting with the MPER epitope and lipids are germline encoded, lending support for the LN01 epitope as a candidate for lineage-based vaccine development. bNAb LN01 neutralizes 92% of a 118-strain virus panel LN01 targets the HIV-1 gp41 MPER, the TM region, and lipids LN01-complexed MPER forms a continuous helix with TM Most LN01 paratope residues interacting with MPER-TM and lipids are germline encoded
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Affiliation(s)
- Dora Pinto
- Institute for Research in Biomedicine, Bellinzona 6500, Ticino, Switzerland
| | - Craig Fenwick
- Swiss Vaccine Research Institute, Lausanne University Hospital, University of Lausanne, 1011 Lausanne, Switzerland
| | - Christophe Caillat
- Institut de Biologie Structurale (IBS), University Grenoble Alpes, CEA, CNRS, 38000 Grenoble, France
| | - Chiara Silacci
- Institute for Research in Biomedicine, Bellinzona 6500, Ticino, Switzerland
| | - Serafima Guseva
- Institut de Biologie Structurale (IBS), University Grenoble Alpes, CEA, CNRS, 38000 Grenoble, France
| | - François Dehez
- LPCT, UMR 7019 Université de Lorraine CNRS, 54500 Vandœuvre-lès-Nancy, France; Laboratoire International Associé CNRS and University of Illinois at Urbana-Champaign, LPCT, UMR 7019 Universiteé de Lorraine CNRS, Vandœuvre-lès-Nancy 54500, France
| | - Christophe Chipot
- LPCT, UMR 7019 Université de Lorraine CNRS, 54500 Vandœuvre-lès-Nancy, France; Laboratoire International Associé CNRS and University of Illinois at Urbana-Champaign, LPCT, UMR 7019 Universiteé de Lorraine CNRS, Vandœuvre-lès-Nancy 54500, France; Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Sonia Barbieri
- Institute for Research in Biomedicine, Bellinzona 6500, Ticino, Switzerland
| | - Andrea Minola
- Humabs Biomed SA, Vir Biotechnology, 6500 Bellinzona, Ticino, Switzerland
| | - David Jarrossay
- Institute for Research in Biomedicine, Bellinzona 6500, Ticino, Switzerland
| | - Georgia D Tomaras
- Duke Human Vaccine Institute, Durham, NC 27710, USA; Paris Diderot University, Sorbonne Paris Cité, Paris 75013, France
| | | | - Agostino Riva
- Department of Biomedical and Clinical Sciences, Luigi Sacco University Hospital, Università di Milano, 20157 Milan, Italy; III Division of Infectious Diseases, ASST Fatebenefratelli-Sacco, 20157 Milan, Italy
| | - Maciej Tarkowski
- Department of Biomedical and Clinical Sciences, Luigi Sacco University Hospital, Università di Milano, 20157 Milan, Italy
| | - Olivier Schwartz
- Institut Pasteur, Virus & Immunity Unit, CNRS UMR 3569, Paris 75015, France; Vaccine Research Institute, 94000 Créteil, France
| | - Timothée Bruel
- Institut Pasteur, Virus & Immunity Unit, CNRS UMR 3569, Paris 75015, France; Vaccine Research Institute, 94000 Créteil, France
| | - Jérémy Dufloo
- Institut Pasteur, Virus & Immunity Unit, CNRS UMR 3569, Paris 75015, France; Vaccine Research Institute, 94000 Créteil, France; Paris Diderot University, Sorbonne Paris Cité, Paris 75013, France
| | - Michael S Seaman
- Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
| | - David C Montefiori
- Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA
| | | | - Davide Corti
- Humabs Biomed SA, Vir Biotechnology, 6500 Bellinzona, Ticino, Switzerland.
| | - Giuseppe Pantaleo
- Swiss Vaccine Research Institute, Lausanne University Hospital, University of Lausanne, 1011 Lausanne, Switzerland; Service of Immunology and Allergy, Lausanne University Hospital, University of Lausanne, 1011 Lausanne, Switzerland.
| | - Winfried Weissenhorn
- Institut de Biologie Structurale (IBS), University Grenoble Alpes, CEA, CNRS, 38000 Grenoble, France.
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6
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Leemans A, Boeren M, Van der Gucht W, Pintelon I, Roose K, Schepens B, Saelens X, Bailey D, Martinet W, Caljon G, Maes L, Cos P, Delputte P. Removal of the N-Glycosylation Sequon at Position N116 Located in p27 of the Respiratory Syncytial Virus Fusion Protein Elicits Enhanced Antibody Responses after DNA Immunization. Viruses 2018; 10:E426. [PMID: 30110893 PMCID: PMC6115940 DOI: 10.3390/v10080426] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 08/08/2018] [Accepted: 08/13/2018] [Indexed: 11/16/2022] Open
Abstract
Prevention of severe lower respiratory tract infections in infants caused by the human respiratory syncytial virus (hRSV) remains a major public health priority. Currently, the major focus of vaccine development relies on the RSV fusion (F) protein since it is the main target protein for neutralizing antibodies induced by natural infection. The protein conserves 5 N-glycosylation sites, two of which are located in the F2 subunit (N27 and N70), one in the F1 subunit (N500) and two in the p27 peptide (N116 and N126). To study the influence of the loss of one or more N-glycosylation sites on RSV F immunogenicity, BALB/c mice were immunized with plasmids encoding RSV F glycomutants. In comparison with F WT DNA immunized mice, higher neutralizing titres were observed following immunization with F N116Q. Moreover, RSV A2-K-line19F challenge of mice that had been immunized with mutant F N116Q DNA was associated with lower RSV RNA levels compared with those in challenged WT F DNA immunized animals. Since p27 is assumed to be post-translationally released after cleavage and thus not present on the mature RSV F protein, it remains to be elucidated how deletion of this glycan can contribute to enhanced antibody responses and protection upon challenge. These findings provide new insights to improve the immunogenicity of RSV F in potential vaccine candidates.
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MESH Headings
- Animals
- Antibodies, Neutralizing/biosynthesis
- Antibodies, Neutralizing/blood
- Antibodies, Viral/biosynthesis
- Antibodies, Viral/blood
- Female
- Glycosylation
- Humans
- Hydrolysis
- Immunization
- Mice
- Mice, Inbred BALB C
- Models, Molecular
- Mutation
- Plasmids/administration & dosage
- Plasmids/genetics
- Plasmids/immunology
- Protein Engineering
- Protein Subunits/administration & dosage
- Protein Subunits/genetics
- Protein Subunits/immunology
- Respiratory Syncytial Virus Infections/immunology
- Respiratory Syncytial Virus Infections/prevention & control
- Respiratory Syncytial Virus Infections/virology
- Respiratory Syncytial Virus Vaccines/administration & dosage
- Respiratory Syncytial Virus Vaccines/genetics
- Respiratory Syncytial Virus Vaccines/immunology
- Respiratory Syncytial Virus, Human/drug effects
- Respiratory Syncytial Virus, Human/genetics
- Respiratory Syncytial Virus, Human/immunology
- Vaccines, DNA/administration & dosage
- Vaccines, DNA/genetics
- Vaccines, DNA/immunology
- Viral Fusion Proteins/administration & dosage
- Viral Fusion Proteins/genetics
- Viral Fusion Proteins/immunology
- Viral Load/drug effects
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Affiliation(s)
- Annelies Leemans
- Laboratory of Microbiology, Parasitology and Hygiene, University of Antwerp, B-2610 Antwerp, Belgium.
| | - Marlies Boeren
- Laboratory of Microbiology, Parasitology and Hygiene, University of Antwerp, B-2610 Antwerp, Belgium.
| | - Winke Van der Gucht
- Laboratory of Microbiology, Parasitology and Hygiene, University of Antwerp, B-2610 Antwerp, Belgium.
| | - Isabel Pintelon
- Laboratory of Cell Biology and Histology, University of Antwerp, B-2610 Antwerp, Belgium.
| | - Kenny Roose
- Medical Biotechnology Centre, VIB, B-9052 Ghent, Belgium.
- Department of Biomedical Molecular Biology, Ghent University, B-9052 Ghent, Belgium.
| | - Bert Schepens
- Medical Biotechnology Centre, VIB, B-9052 Ghent, Belgium.
- Department of Biomedical Molecular Biology, Ghent University, B-9052 Ghent, Belgium.
| | - Xavier Saelens
- Medical Biotechnology Centre, VIB, B-9052 Ghent, Belgium.
- Department of Biomedical Molecular Biology, Ghent University, B-9052 Ghent, Belgium.
| | | | - Wim Martinet
- Laboratory of Physiopharmacology, University of Antwerp, B-2610 Antwerp, Belgium.
| | - Guy Caljon
- Laboratory of Microbiology, Parasitology and Hygiene, University of Antwerp, B-2610 Antwerp, Belgium.
| | - Louis Maes
- Laboratory of Microbiology, Parasitology and Hygiene, University of Antwerp, B-2610 Antwerp, Belgium.
| | - Paul Cos
- Laboratory of Microbiology, Parasitology and Hygiene, University of Antwerp, B-2610 Antwerp, Belgium.
| | - Peter Delputte
- Laboratory of Microbiology, Parasitology and Hygiene, University of Antwerp, B-2610 Antwerp, Belgium.
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7
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Cao Y, Dong Y, Chou JJ. Structural and Functional Properties of Viral Membrane Proteins. ADVANCES IN MEMBRANE PROTEINS 2018. [PMCID: PMC7122571 DOI: 10.1007/978-981-13-0532-0_6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Viruses have developed a large variety of transmembrane proteins to carry out their infectious cycles. Some of these proteins are simply anchored to membrane via transmembrane helices. Others, however, adopt more interesting structures to perform tasks such as mediating membrane fusion and forming ion-permeating channels. Due to the dynamic or plastic nature shown by many of the viral membrane proteins, structural and mechanistic understanding of these proteins has lagged behind their counterparts in prokaryotes and eukaryotes. This chapter provides an overview of the use of NMR spectroscopy to unveil the transmembrane and membrane-proximal regions of viral membrane proteins, as well as their interactions with potential therapeutics.
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Affiliation(s)
- Yu Cao
- Institute of Precision Medicine, The Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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8
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Liu D, Wang H, Yamamoto M, Song J, Zhang R, Du Q, Kawaguchi Y, Inoue JI, Matsuda Z. Six-helix bundle completion in the distal C-terminal heptad repeat region of gp41 is required for efficient human immunodeficiency virus type 1 infection. Retrovirology 2018; 15:27. [PMID: 29609648 PMCID: PMC5879932 DOI: 10.1186/s12977-018-0410-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Accepted: 03/22/2018] [Indexed: 11/16/2022] Open
Abstract
Background The native pre-fusion structure of gp120/gp41 complex of human immunodeficiency virus type 1 was recently revealed. In the model, the helices of gp41 (α6, α7, α8, and α9) form a four-helix collar underneath trimeric gp120. Gp41 is a class I fusion protein and mediates membrane fusion by forming a post-fusion structure called the six-helix bundle (6HB). The comparison of the pre- and post-fusion structures revealed the large conformational changes in gp41 during the antiparallel packing of the N- and C-terminal heptad repeats (NHRs and CHRs) in membrane fusion. Several mutagenesis studies of gp41 performed in the past were interpreted based on 6HB, the only available structure at that time. To obtain an insight about the current pre-fusion structural model and conformational changes during membrane fusion, alanine insertion mutagenesis of the NHR, CHR and connecting loop regions of HXB2 gp41 was performed. The effects of mutations on biosynthesis and membrane fusion were analyzed by immunoblotting and fusion assays, respectively. The extent of membrane fusion was evaluated by split luciferase-based pore formation and syncytia formation assays, respectively. Results Consistent with the current structural model, drastic negative effects of mutations on biosynthesis and membrane fusion were observed for NHR, loop, and proximal regions of CHR (up to amino acid position 643). The insertions in α9 after it leaves the four-helix collar were tolerable for biosynthesis. These CHR mutants showed varying effects on membrane fusion. Insertion at position 644 or 645 resulted in poor pore and syncytia formation. Efficient pore and syncytia formation almost similar to that of the wild type was observed for insertion at position 647, 648 or 649. However, recovery of virus infectivity was only observed for the insertions beyond position 648. Conclusions The mutagenesis data for HXB2 gp41 is in agreement with the recent pre-fusion structure model. The virus infection data suggested that fusion pores sufficiently large enough for the release of the virus genome complex are formed after the completion of 6HB beyond position 648. Electronic supplementary material The online version of this article (10.1186/s12977-018-0410-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Dehua Liu
- Laboratory of Structural Virology and Immunology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,The Chinese University of Hong Kong, Sha Tin, Hong Kong, China
| | - Hongyun Wang
- Laboratory of Structural Virology and Immunology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Mizuki Yamamoto
- Research Center for Asian Infectious Diseases, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo, 108-8639, Japan.,Division of Cellular and Molecular Biology, Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Jiping Song
- Laboratory of Structural Virology and Immunology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Rui Zhang
- Laboratory of Structural Virology and Immunology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Qingling Du
- Laboratory of Structural Virology and Immunology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Yasushi Kawaguchi
- Research Center for Asian Infectious Diseases, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo, 108-8639, Japan.,Division of Molecular Virology, Department of Microbiology and Immunology, Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Jun-Ichiro Inoue
- Division of Cellular and Molecular Biology, Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Zene Matsuda
- Laboratory of Structural Virology and Immunology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China. .,Research Center for Asian Infectious Diseases, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo, 108-8639, Japan.
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9
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Liang S, Ratnayake PU, Keinath C, Jia L, Wolfe R, Ranaweera A, Weliky DP. Efficient Fusion at Neutral pH by Human Immunodeficiency Virus gp41 Trimers Containing the Fusion Peptide and Transmembrane Domains. Biochemistry 2018; 57:1219-1235. [PMID: 29345922 DOI: 10.1021/acs.biochem.7b00753] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Human immunodeficiency virus (HIV) is membrane-enveloped, and an initial infection step is joining/fusion of viral and cell membranes. This step is catalyzed by gp41, which is a single-pass integral viral membrane protein. The protein contains an ∼170-residue ectodomain located outside the virus that is important for fusion and includes the fusion peptide (FP), N-helix, loop, C-helix, and viral membrane-proximal external region (MPER). The virion initially has noncovalent complexes between three gp41 ectodomains and three gp120 proteins. A gp120 contains ∼500 residues and functions to identify target T-cells and macrophages via binding to specific protein receptors of the target cell membrane. gp120 moves away from the gp41 ectodomain, and the ectodomain is thought to bind to the target cell membrane and mediate membrane fusion. The secondary and tertiary structures of the ectodomain are different in the initial complex with gp120 and the final state without gp120. There is not yet imaging of gp41 during fusion, so the temporal relationship between the gp41 and membrane structures is not known. This study describes biophysical and functional characterization of large gp41 constructs that include the ectodomain and transmembrane domain (TM). Significant fusion is observed of both neutral and anionic vesicles at neutral pH, which reflects the expected conditions of HIV/cell fusion. Fusion is enhanced by the FP, which in HIV/cell fusion likely contacts the host membrane, and the MPER and TM, which respectively interfacially contact and traverse the HIV membrane. Initial contact with vesicles is made by protein trimers that are in a native oligomeric state that reflects the initial complex with gp120 and also is commonly observed for the ectodomain without gp120. Circular dichroism data support helical structure for the N-helix, C-helix, and MPER and nonhelical structure for the FP and loop. Distributions of monomer, trimer, and hexamer states are observed by size-exclusion chromatography (SEC), with dependences on solubilizing detergent and construct. These SEC and other data are integrated into a refined working model of HIV/cell fusion that includes dissociation of the ectodomain into gp41 monomers followed by folding into hairpins that appose the two membranes, and subsequent fusion catalysis by trimers and hexamers of hairpins. The monomer and oligomer gp41 states may therefore satisfy dual requirements for HIV entry of membrane apposition and fusion.
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Affiliation(s)
- S Liang
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - P U Ratnayake
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - C Keinath
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - L Jia
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - R Wolfe
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - A Ranaweera
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - D P Weliky
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
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10
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Piai A, Dev J, Fu Q, Chou JJ. Stability and Water Accessibility of the Trimeric Membrane Anchors of the HIV-1 Envelope Spikes. J Am Chem Soc 2017; 139:18432-18435. [PMID: 29193965 DOI: 10.1021/jacs.7b09352] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
HIV-1 envelope spike (Env) is a type I membrane protein that mediates viral entry. Recent studies showed that its transmembrane domain (TMD) forms a trimer in lipid bilayer whose structure has several peculiar features that remain difficult to explain. One is the presence of an arginine R696 in the middle of the TM helix. Additionally, the N- and C-terminal halves of the TM helix form trimeric cores of opposite nature (hydrophobic and hydrophilic, respectively). Here we determined the membrane partition and solvent accessibility of the TMD in bicelles that mimic a lipid bilayer. Solvent paramagnetic relaxation enhancement analysis showed that the R696 is indeed positioned close to the center of the bilayer, but, surprisingly, can exchange rapidly with water as indicated by hydrogen-deuterium exchange measurements. The solvent accessibility of R696 is likely mediated by the hydrophilic core, which also showed fast water exchange. In contrast, the N-terminal hydrophobic core showed extremely slow solvent exchange, suggesting the trimer formed by this region is extraordinarily stable. Our data explain how R696 is accommodated in the middle of the membrane while reporting the overall stability of the Env TMD trimer in lipid bilayer.
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Affiliation(s)
- Alessandro Piai
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School , Boston, Massachusetts 02115, United States
| | - Jyoti Dev
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School , Boston, Massachusetts 02115, United States
| | - Qingshan Fu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School , Boston, Massachusetts 02115, United States
| | - James J Chou
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School , Boston, Massachusetts 02115, United States
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Chen B, Chou JJ. Structure of the transmembrane domain of HIV-1 envelope glycoprotein. FEBS J 2016; 284:1171-1177. [PMID: 27868386 DOI: 10.1111/febs.13954] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Accepted: 11/02/2016] [Indexed: 12/15/2022]
Abstract
HIV-1 envelope spike (Env) is a heavily glycosylated, type I membrane protein that mediates fusion of viral and cell membranes to initiate infection. It is also a primary target of neutralizing antibodies and thus an important candidate for vaccine development. We have recently reported a nuclear magnetic resonance structure of the transmembrane (TM) domain of HIV-1 Env reconstituted in a membrane-like environment. Taking HIV-1 as an example, we discuss here how a TM domain can anchor, stabilize, and modulate a viral envelope spike and how its high-resolution structure can contribute to understanding viral membrane fusion and to immunogen design.
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Affiliation(s)
- Bing Chen
- Division of Molecular Medicine, Department of Pediatrics, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - James J Chou
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
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Saw WT, Matsuda Z, Eisenberg RJ, Cohen GH, Atanasiu D. Using a split luciferase assay (SLA) to measure the kinetics of cell-cell fusion mediated by herpes simplex virus glycoproteins. Methods 2015; 90:68-75. [PMID: 26022509 DOI: 10.1016/j.ymeth.2015.05.021] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2015] [Revised: 05/20/2015] [Accepted: 05/22/2015] [Indexed: 02/08/2023] Open
Abstract
Herpes simplex virus (HSV) entry and cell-cell fusion require the envelope proteins gD, gH/gL and gB. We propose that receptor-activated conformational changes to gD activate gH/gL, which then triggers gB (the fusogen) into an active form. To study this dynamic process, we have adapted a dual split protein assay originally developed to study the kinetics of human immunodeficiency virus (HIV) mediated fusion. This assay uses a chimera of split forms of renilla luciferase (RL) and green fluorescent protein (GFP). Effector cells are co-transfected with the glycoproteins and one of the split reporters. Receptor-bearing target cells are transfected with the second reporter. Co-culture results in fusion and restoration of RL, which can convert a membrane permeable substrate into a luminescent product, thereby enabling one to monitor initiation and extent of fusion in live cells in real time. Restoration of GFP can also be studied by fluorescence microscopy. Two sets of split reporters have been developed: the original one allows one to measure fusion kinetics over hours whereas the more recent version was designed to enhance the sensitivity of RL activity allowing one to monitor both initiation and rates of fusion in minutes. Here, we provide a detailed, step-by-step protocol for the optimization of the assay (which we call the SLA for split luciferase assay) using the HSV system. We also show several examples of the power of this assay to examine both the initiation and kinetics of cell-cell fusion by wild type forms of gD, gB, gH/gL of both serotypes of HSV as well as the effect of mutations and antibodies that alter the kinetics of fusion. The SLA can be applied to other viral systems that carry out membrane fusion.
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Affiliation(s)
- Wan Ting Saw
- Department of Microbiology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States.
| | - Zene Matsuda
- Research Center for Asian Infectious Diseases, Institute of Medical Science, University of Tokyo, Shirokanedai, Minato-ku, Tokyo, Japan; China-Japan Joint Laboratory of Structural Virology and Immunology, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, PR China.
| | - Roselyn J Eisenberg
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States.
| | - Gary H Cohen
- Department of Microbiology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States.
| | - Doina Atanasiu
- Department of Microbiology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States.
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Co-expression of foreign proteins tethered to HIV-1 envelope glycoprotein on the cell surface by introducing an intervening second membrane-spanning domain. PLoS One 2014; 9:e96790. [PMID: 24804933 PMCID: PMC4013048 DOI: 10.1371/journal.pone.0096790] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 04/11/2014] [Indexed: 11/19/2022] Open
Abstract
The envelope glycoprotein (Env) of human immunodeficiency virus type I (HIV-1) mediates membrane fusion. To analyze the mechanism of HIV-1 Env-mediated membrane fusion, it is desirable to determine the expression level of Env on the cell surface. However, the quantification of Env by immunological staining is often hampered by the diversity of HIV-1 Env and limited availability of universal antibodies that recognize different Envs with equal efficiency. To overcome this problem, here we linked a tag protein called HaloTag at the C-terminus of HIV-1 Env. To relocate HaloTag to the cell surface, we introduced a second membrane-spanning domain (MSD) between Env and HaloTag. The MSD of transmembrane protease serine 11D, a type II transmembrane protein, successfully relocated HaloTag to the cell surface. The surface level of Env can be estimated indirectly by staining HaloTag with a specific membrane-impermeable fluorescent ligand. This tagging did not compromise the fusogenicity of Env drastically. Furthermore, fusogenicity of Env was preserved even after the labeling with the ligands. We have also found that an additional foreign peptide or protein such as C34 or neutralizing single-chain variable fragment (scFv) can be linked to the C-terminus of the HaloTag protein. Using these constructs, we were able to determine the required length of C34 and critical residues of neutralizing scFv for blocking membrane fusion, respectively.
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Kuhlmann AS, Steckbeck JD, Sturgeon TJ, Craigo JK, Montelaro RC. Unique functional properties of conserved arginine residues in the lentivirus lytic peptide domains of the C-terminal tail of HIV-1 gp41. J Biol Chem 2014; 289:7630-40. [PMID: 24497632 PMCID: PMC3953275 DOI: 10.1074/jbc.m113.529339] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Revised: 01/20/2014] [Indexed: 11/06/2022] Open
Abstract
A previous study from our laboratory reported a preferential conservation of arginine relative to lysine in the C-terminal tail (CTT) of HIV-1 envelope (Env). Despite substantial overall sequence variation in the CTT, specific arginines are highly conserved in the lentivirus lytic peptide (LLP) motifs and are scarcely substituted by lysines, in contrast to gp120 and the ectodomain of gp41. However, to date, no explanation has been provided to explain the selective incorporation and conservation of arginines over lysines in these motifs. Herein, we address the functions in virus replication of the most conserved arginines by performing conservative mutations of arginine to lysine in the LLP1 and LLP2 motifs. The presence of lysine in place of arginine in the LLP1 motif resulted in significant impairment of Env expression and consequently virus replication kinetics, Env fusogenicity, and incorporation. By contrast, lysine exchanges in LLP2 only affected the level of Env incorporation and fusogenicity. Our findings demonstrate that the conservative lysine substitutions significantly affect Env functional properties indicating a unique functional role for the highly conserved arginines in the LLP motifs. These results provide for the first time a functional explanation to the preferred incorporation of arginine, relative to lysine, in the CTT of HIV-1 Env. We propose that these arginines may provide unique functions for Env interaction with viral or cellular cofactors that then influence overall Env functional properties.
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Affiliation(s)
- Anne-Sophie Kuhlmann
- From the Center for Vaccine Research and
- the Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Jonathan D. Steckbeck
- From the Center for Vaccine Research and
- the Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | | | - Jodi K. Craigo
- From the Center for Vaccine Research and
- the Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Ronald C. Montelaro
- From the Center for Vaccine Research and
- the Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
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15
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Characterization of the water defect at the HIV-1 gp41 membrane spanning domain in bilayers with and without cholesterol using molecular simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:1396-405. [PMID: 24440660 DOI: 10.1016/j.bbamem.2014.01.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 12/24/2013] [Accepted: 01/08/2014] [Indexed: 12/23/2022]
Abstract
The membrane spanning domain (MSD) of human immunodeficiency virus 1 (HIV-1) envelope glycoprotein gp41 is important for fusion and infection. We used molecular dynamics (MD) simulations (3.4 μs total) to relate membrane and peptide properties that lead to water solvation of the α-helical gp41 MSD's midspan arginine in pure dipalmitoylphosphatidylcholine (DPPC) and in 50/50 DPPC/cholesterol membranes. We find that the midspan arginine is solvated by water that penetrates the inner leaflet, leading to a so-called water defect. The water defect is surprisingly robust across initial conditions and membrane compositions, but the presence of cholesterol modulates its behavior in several key ways. In the cholesterol-containing membranes, fluctuations in membrane thickness and water penetration depth are localized near the midspan arginine, and the MSD helices display a tightly regulated tilt angle. In the cholesterol-free membranes, thickness fluctuations are not as strongly correlated to the peptide position and tilt angles vary significantly depending on protein position relative to boundaries between domains of differing thickness. Cholesterol in an HIV-1 viral membrane is required for infection. Therefore, this work suggests that the colocalized water defect and membrane thickness fluctuations in cholesterol-containing viral membranes play an important role in fusion by bringing the membrane closer to a stability limit that must be crossed for fusion to occur.
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16
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[Joint collaboration in infectious diseases in China, the University of Tokyo]. Uirusu 2013; 63:37-44. [PMID: 24769576 DOI: 10.2222/jsv.63.37] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Recent rapid developments in Asian and African countries bring an opportunity of cross-species transmission of pathogens through unprecedented contacts between people and wild animals. Furthermore, increase of global exchanges of people and products facilitates a rapid spread of infectious diseases worldwide. China has an enormous population with diverse ethnic groups within its wide territory; furthermore, it is experiencing very rapid urbanization. These conditions make China a potential epicenter of emerging infectious diseases. One good example is the SARS incidence in 2003. Therefore, it is essential to include China in a network of research groups of infectious diseases. Here we summarize the ongoing collaborations between the Institute of Medical Science, the University of Tokyo, and its Chinese counterparts.
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Ishikawa H, Meng F, Kondo N, Iwamoto A, Matsuda Z. Generation of a dual-functional split-reporter protein for monitoring membrane fusion using self-associating split GFP. Protein Eng Des Sel 2012; 25:813-20. [PMID: 22942393 DOI: 10.1093/protein/gzs051] [Citation(s) in RCA: 100] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Split reporter proteins capable of self-association and reactivation have applications in biomedical research, but designing these proteins, especially the selection of appropriate split points, has been somewhat arbitrary. We describe a new methodology to facilitate generating split proteins using split GFP as a self-association module. We first inserted the entire GFP module at one of several candidate split points in the protein of interest, and chose clones that retained the GFP signal and high activity relative to the original protein. Once such chimeric clones were identified, a final pair of split proteins was generated by splitting the GFP-inserted chimera within the GFP domain. Applying this strategy to Renilla reniformis luciferase, we identified a new split point that gave 10 times more activity than the previous split point. The process of membrane fusion was monitored with high sensitivity using a new pair of split reporter proteins. We also successfully identified new split points for HaloTag protein and firefly luciferase, generating pairs of self-associating split proteins that recovered the functions of both GFP and the original protein. This simple method of screening will facilitate the designing of split proteins that are capable of self-association through the split GFP domains.
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Affiliation(s)
- Hirohito Ishikawa
- Research Center for Asian Infectious Diseases, Institute of Medical Science, University of Tokyo, Shirokanedai, Minato-ku, Tokyo, Japan
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18
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Ahmad A, Cao X. Plant PRMTs broaden the scope of arginine methylation. J Genet Genomics 2012; 39:195-208. [PMID: 22624881 DOI: 10.1016/j.jgg.2012.04.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 04/02/2012] [Accepted: 04/02/2012] [Indexed: 01/22/2023]
Abstract
Post-translational methylation at arginine residues is one of the most important covalent modifications of proteins, involved in a myriad of essential cellular processes in eukaryotes, such as transcriptional regulation, RNA processing, signal transduction, and DNA repair. Methylation at arginine residues is catalyzed by a family of enzymes called protein arginine methyltransferases (PRMTs). PRMTs have been extensively studied in various taxa and there is a growing tendency to unveil their functional importance in plants. Recent studies in plants revealed that this evolutionarily conserved family of enzymes regulates essential traits including vegetative growth, flowering time, circadian cycle, and response to high medium salinity and ABA. In this review, we highlight recent advances in the field of post-translational arginine methylation with special emphasis on the roles and future prospects of this modification in plants.
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Affiliation(s)
- Ayaz Ahmad
- State Key Laboratory of Plant Genomics and National Center for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road #5, Beijing 100101, China
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Reuven EM, Dadon Y, Viard M, Manukovsky N, Blumenthal R, Shai Y. HIV-1 gp41 transmembrane domain interacts with the fusion peptide: implication in lipid mixing and inhibition of virus-cell fusion. Biochemistry 2012; 51:2867-78. [PMID: 22413880 PMCID: PMC3335273 DOI: 10.1021/bi201721r] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fusion of the human immunodeficiency virus (HIV) with target cells is mediated by the gp41 subunit of the envelope protein. Mutation and deletion studies within the transmembrane domain (TMD) of intact gp41 influenced its fusion activity. In addition, current models suggest that the TMD is in proximity with the fusion peptide (FP) at the late fusion stages, but there are no direct experimental data to support this hypothesis. Here, we investigated the TMD focusing on two regions: the N-terminal containing the GxxxG motif and the C-terminal containing the GLRI motif, which is conserved among the TMDs of HIV and the T-cell receptor. Studies utilizing the ToxR expression system combined with synthetic peptides and their fluorescent analogues derived from TMD revealed that the GxxxG motif is important for TMD self-association, whereas the C-terminal region is for its heteroassociation with FP. Functionally, all three TMD peptides induced lipid mixing that was enhanced significantly upon mixing with FP. Furthermore, the TMD peptides inhibited virus-cell fusion apparently through their interaction with their endogenous counterparts. Notably, the R2E mutant (in the GLRI) was significantly less potent than the two others. Overall, our findings provide experimental evidence that HIV-1 TMD contributes to membrane assembly and function of the HIV-1 envelope. Owing to similarities between functional domains within viruses, these findings suggest that the TMDs and FPs may contribute similarly in other viruses as well.
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Affiliation(s)
- Eliran Moshe Reuven
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, 76100 Israel
| | - Yakir Dadon
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, 76100 Israel
| | - Mathias Viard
- Basic Research Program, SAIC-Frederick, Inc., NCI-Frederick, Frederick, Maryland 21702
- Nanobiology Program, Center of Cancer Research, National Cancer Institute, Frederick, Maryland, USA
| | - Nurit Manukovsky
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, 76100 Israel
| | - Robert Blumenthal
- Basic Research Program, SAIC-Frederick, Inc., NCI-Frederick, Frederick, Maryland 21702
| | - Yechiel Shai
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, 76100 Israel
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