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Dutta M, Su Y, Plescia CB, Voth GA, Stahelin RV. The SARS-CoV-2 nucleoprotein associates with anionic lipid membranes. J Biol Chem 2024; 300:107456. [PMID: 38866325 PMCID: PMC11298601 DOI: 10.1016/j.jbc.2024.107456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 05/30/2024] [Accepted: 06/01/2024] [Indexed: 06/14/2024] Open
Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a lipid-enveloped virus that acquires its lipid bilayer from the host cell it infects. SARS-CoV-2 can spread from cell to cell or from patient to patient by undergoing assembly and budding to form new virions. The assembly and budding of SARS-CoV-2 is mediated by several structural proteins known as envelope (E), membrane (M), nucleoprotein (N), and spike (S), which can form virus-like particles (VLPs) when co-expressed in mammalian cells. Assembly and budding of SARS-CoV-2 from the host ER-Golgi intermediate compartment is a critical step in the virus acquiring its lipid bilayer. To date, little information is available on how SARS-CoV-2 assembles and forms new viral particles from host membranes. In this study, we used several lipid binding assays and found the N protein can strongly associate with anionic lipids including phosphoinositides and phosphatidylserine. Moreover, we show lipid binding occurs in the N protein C-terminal domain, which is supported by extensive in silico analysis. We demonstrate anionic lipid binding occurs for both the free and the N oligomeric forms, suggesting N can associate with membranes in the nucleocapsid form. Based on these results, we present a lipid-dependent model based on in vitro, cellular, and in silico data for the recruitment of N to assembly sites in the lifecycle of SARS-CoV-2.
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Affiliation(s)
- Mandira Dutta
- Department of Chemistry, The University of Chicago, Chicago, Illinois, USA
| | - Yuan Su
- Department of Medicinal Chemistry and Molecular Pharmacology and the Purdue Institute of Inflammation, Immunology and Infectious Disease, Purdue University, West Lafayette, Indiana, USA
| | - Caroline B Plescia
- Department of Medicinal Chemistry and Molecular Pharmacology and the Purdue Institute of Inflammation, Immunology and Infectious Disease, Purdue University, West Lafayette, Indiana, USA
| | - Gregory A Voth
- Department of Chemistry, The University of Chicago, Chicago, Illinois, USA; Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics, and James Frank Institute, The University of Chicago, Chicago, Illinois, USA.
| | - Robert V Stahelin
- Department of Medicinal Chemistry and Molecular Pharmacology and the Purdue Institute of Inflammation, Immunology and Infectious Disease, Purdue University, West Lafayette, Indiana, USA.
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2
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Dutta M, Su Y, Voth GA, Stahelin RV. The SARS-CoV-2 nucleoprotein associates with anionic lipid membranes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.15.557899. [PMID: 37745364 PMCID: PMC10516002 DOI: 10.1101/2023.09.15.557899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/26/2023]
Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a lipid-enveloped virus that acquires its lipid bilayer from the host cell it infects. SARS-CoV-2 can spread from cell to cell or from patient to patient by undergoing assembly and budding to form new virions. The assembly and budding of SARS-CoV-2 is mediated by several structural proteins known as envelope (E), membrane (M), nucleoprotein (N) and spike (S), which can form virus-like particles (VLPs) when co-expressed in mammalian cells. Assembly and budding of SARS-CoV-2 from the host ER-Golgi intermediate compartment is a critical step in the virus acquiring its lipid bilayer. To date, little information is available on how SARS-CoV-2 assembles and forms new viral particles from host membranes. In this study, we find the N protein can strongly associate with anionic lipids including phosphoinositides and phosphatidylserine. Moreover, lipid binding is shown to occur in the N protein C-terminal domain, which is supported by extensive in silico analysis. Anionic lipid binding occurs for both the free and N oligomeric forms suggesting N can associate with membranes in the nucleocapsid form. Herein we present a lipid-dependent model based on in vitro, cellular and in silico data for the recruitment of N to M assembly sites in the lifecycle of SARS-CoV-2.
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Affiliation(s)
- Mandira Dutta
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics, and James Frank Institute, The University of Chicago, Chicago, IL, USA
| | - Yuan Su
- Department of Medicinal Chemistry and Molecular Pharmacology and the Purdue Institute of Inflammation, Immunology and Infectious Disease, Purdue University, West Lafayette, IN, USA
| | - Gregory A. Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics, and James Frank Institute, The University of Chicago, Chicago, IL, USA
| | - Robert V. Stahelin
- Department of Medicinal Chemistry and Molecular Pharmacology and the Purdue Institute of Inflammation, Immunology and Infectious Disease, Purdue University, West Lafayette, IN, USA
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3
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An infectious Rous Sarcoma Virus Gag mutant that is defective in nuclear cycling. J Virol 2021; 95:e0064821. [PMID: 34319154 DOI: 10.1128/jvi.00648-21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
During retroviral replication, unspliced viral genomic RNA (gRNA) must escape the nucleus for translation into viral proteins and packaging into virions. "Complex" retroviruses such as Human Immunodeficiency Virus (HIV) use cis-acting elements on the unspliced gRNA in conjunction with trans-acting viral proteins to facilitate this escape. "Simple" retroviruses such as Mason-Pfizer Monkey Virus (MPMV) and Murine Leukemia Virus (MLV) exclusively use cis-acting elements on the gRNA in conjunction with host nuclear export proteins for nuclear escape. Uniquely, the simple retrovirus Rous Sarcoma Virus (RSV) has a Gag structural protein that cycles through the nucleus prior to plasma membrane binding. This trafficking has been implicated in facilitating gRNA nuclear export and is thought to be a required mechanism. Previously described mutants that abolish nuclear cycling displayed enhanced plasma membrane binding, enhanced virion release, and a significant loss in genome incorporation resulting in loss of infectivity. Here, we describe a nuclear cycling deficient RSV Gag mutant that has similar plasma membrane binding and genome incorporation to WT virus and surprisingly, is replication competent albeit with a slower rate of spread compared to WT. This mutant suggests that RSV Gag nuclear cycling is not strictly required for RSV replication. Importance While mechanisms for retroviral Gag assembly at the plasma membrane are beginning to be characterized, characterization of intermediate trafficking locales remain elusive. This is in part due to the difficulty of tracking individual proteins from translation to plasma membrane binding. RSV Gag nuclear cycling is a unique phenotype that may provide comparative insight to viral trafficking evolution and may present a model intermediate to cis- and trans-acting mechanisms for gRNA export.
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Rendezvous at Plasma Membrane: Cellular Lipids and tRNA Set up Sites of HIV-1 Particle Assembly and Incorporation of Host Transmembrane Proteins. Viruses 2020; 12:v12080842. [PMID: 32752131 PMCID: PMC7472227 DOI: 10.3390/v12080842] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2020] [Revised: 07/20/2020] [Accepted: 07/24/2020] [Indexed: 12/28/2022] Open
Abstract
The HIV-1 structural polyprotein Gag drives the virus particle assembly specifically at the plasma membrane (PM). During this process, the nascent virion incorporates specific subsets of cellular lipids and host membrane proteins, in addition to viral glycoproteins and viral genomic RNA. Gag binding to the PM is regulated by cellular factors, including PM-specific phospholipid PI(4,5)P2 and tRNAs, both of which bind the highly basic region in the matrix domain of Gag. In this article, we review our current understanding of the roles played by cellular lipids and tRNAs in specific localization of HIV-1 Gag to the PM. Furthermore, we examine the effects of PM-bound Gag on the organization of the PM bilayer and discuss how the reorganization of the PM at the virus assembly site potentially contributes to the enrichment of host transmembrane proteins in the HIV-1 particle. Since some of these host transmembrane proteins alter release, attachment, or infectivity of the nascent virions, the mechanism of Gag targeting to the PM and the nature of virus assembly sites have major implications in virus spread.
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5
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Rous Sarcoma Virus Genomic RNA Dimerization Capability In Vitro Is Not a Prerequisite for Viral Infectivity. Viruses 2020; 12:v12050568. [PMID: 32455905 PMCID: PMC7291142 DOI: 10.3390/v12050568] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 05/19/2020] [Accepted: 05/20/2020] [Indexed: 12/29/2022] Open
Abstract
Retroviruses package their full-length, dimeric genomic RNA (gRNA) via specific interactions between the Gag polyprotein and a “Ψ” packaging signal located in the gRNA 5′-UTR. Rous sarcoma virus (RSV) gRNA has a contiguous, well-defined Ψ element, that directs the packaging of heterologous RNAs efficiently. The simplicity of RSV Ψ makes it an informative model to examine the mechanism of retroviral gRNA packaging, which is incompletely understood. Little is known about the structure of dimerization initiation sites or specific Gag interaction sites of RSV gRNA. Using selective 2′-hydroxyl acylation analyzed by primer extension (SHAPE), we probed the secondary structure of the entire RSV 5′-leader RNA for the first time. We identified a putative bipartite dimerization initiation signal (DIS), and mutation of both sites was required to significantly reduce dimerization in vitro. These mutations failed to reduce viral replication, suggesting that in vitro dimerization results do not strictly correlate with in vivo infectivity, possibly due to additional RNA interactions that maintain the dimers in cells. UV crosslinking-coupled SHAPE (XL-SHAPE) was next used to determine Gag-induced RNA conformational changes, revealing G218 as a critical Gag contact site. Overall, our results suggest that disruption of either of the DIS sequences does not reduce virus replication and reveal specific sites of Gag–RNA interactions.
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6
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Qualley DF, Cooper SE, Ross JL, Olson ED, Cantara WA, Musier-Forsyth K. Solution Conformation of Bovine Leukemia Virus Gag Suggests an Elongated Structure. J Mol Biol 2019; 431:1203-1216. [PMID: 30731090 PMCID: PMC6424597 DOI: 10.1016/j.jmb.2019.01.036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Revised: 01/28/2019] [Accepted: 01/29/2019] [Indexed: 01/13/2023]
Abstract
Bovine leukemia virus (BLV) is a deltaretrovirus that infects domestic cattle. The structural protein Gag, found in all retroviruses, is a polyprotein comprising three major functional domains: matrix (MA), capsid (CA), and nucleocapsid (NC). Previous studies have shown that both mature BLV MA and NC are able to bind to nucleic acids; however, the viral assembly process and packaging of viral genomic RNA requires full-length Gag to produce infectious particles. Compared to lentiviruses, little is known about the structure of the Gag polyprotein of deltaretroviruses. In this work, structural models of full-length BLV Gag and Gag lacking the MA domain were generated based on previous structural data of individual domains, homology modeling, and flexible fitting to SAXS data using molecular dynamics. The models were used in molecular dynamic simulations to determine the relative mobility of the protein backbone. Functional annealing assays revealed the role of MA in the nucleic acid chaperone activity of BLV Gag. Our results show that full-length BLV Gag has an elongated rod-shaped structure that is relatively rigid, with the exception of the linker between the MA and CA domains. Deletion of the MA domain maintains the elongated structure but alters the rate of BLV Gag-facilitated annealing of two complementary nucleic acids. These data are consistent with a role for the MA domain of retroviral Gag proteins in modulating nucleic acid binding and chaperone activity. IMPORTANCE: BLV is a retrovirus that is found worldwide in domestic cattle. Since BLV infection has serious implications for agriculture, and given its similarities to human retroviruses such as HTLV-1, the development of an effective treatment would have numerous benefits. The Gag polyprotein exists in all retroviruses and is a key player in viral assembly. However, the full-length structure of Gag from any virus has yet to be elucidated at high resolution. This study provides structural data for BLV Gag and could be a starting point for modeling Gag-small molecule interactions with the ultimate goal of developing of a new class of pharmaceuticals.
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Affiliation(s)
- Dominic F Qualley
- Department of Chemistry and Biochemistry, and Center for One Health Studies, Berry College, Mt. Berry, GA 30149, USA.
| | - Sarah E Cooper
- Department of Chemistry and Biochemistry, and Center for One Health Studies, Berry College, Mt. Berry, GA 30149, USA
| | - James L Ross
- Department of Chemistry and Biochemistry, and Center for One Health Studies, Berry College, Mt. Berry, GA 30149, USA
| | - Erik D Olson
- Department of Chemistry and Biochemistry, Center for RNA Biology, and Center for Retrovirus Research, Ohio State University, Columbus, OH 43210, USA
| | - William A Cantara
- Department of Chemistry and Biochemistry, Center for RNA Biology, and Center for Retrovirus Research, Ohio State University, Columbus, OH 43210, USA
| | - Karin Musier-Forsyth
- Department of Chemistry and Biochemistry, Center for RNA Biology, and Center for Retrovirus Research, Ohio State University, Columbus, OH 43210, USA
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7
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Watanabe SM, Medina GN, Eastep GN, Ghanam RH, Vlach J, Saad JS, Carter CA. The matrix domain of the Gag protein from avian sarcoma virus contains a PI(4,5)P 2-binding site that targets Gag to the cell periphery. J Biol Chem 2018; 293:18841-18853. [PMID: 30309982 DOI: 10.1074/jbc.ra118.003947] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2018] [Revised: 09/28/2018] [Indexed: 01/08/2023] Open
Abstract
The Gag protein of avian sarcoma virus (ASV) lacks an N-myristoyl (myr) group, but contains structural domains similar to those of HIV-1 Gag. Similarly to HIV-1, ASV Gag accumulates on the plasma membrane (PM) before egress; however, it is unclear whether the phospholipid PI(4,5)P2 binds directly to the matrix (MA) domain of ASV Gag, as is the case for HIV-1 Gag. Moreover, the role of PI(4,5)P2 in ASV Gag localization and budding has been controversial. Here, we report that substitution of residues that define the PI(4,5)P2-binding site in the ASV MA domain (reported in an accompanying paper) interfere with Gag localization to the cell periphery and inhibit the production of virus-like particles (VLPs). We show that co-expression of Sprouty2 (Spry2) or the pleckstrin homology domain of phospholipase Cδ (PH-PLC), two proteins that bind PI(4,5)P2, affects ASV Gag trafficking to the PM and budding. Replacement of the N-terminal 32 residues of HIV-1 MA, which encode its N-terminal myr signal and its PI(4,5)P2-binding site, with the structurally equivalent N-terminal 24 residues of ASV MA created a chimera that localized at the PM and produced VLPs. In contrast, the homologous PI(4,5)P2-binding signal in ASV MA could target HIV-1 Gag to the PM when substituted, but did not support budding. Collectively, these findings reveal a basic patch in both ASV and HIV-1 Gag capable of mediating PM binding and budding for ASV but not for HIV-1 Gag. We conclude that PI(4,5)P2 is a strong determinant of ASV Gag targeting to the PM and budding.
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Affiliation(s)
- Susan M Watanabe
- From the Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, New York 11794 and
| | - Gisselle N Medina
- From the Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, New York 11794 and
| | - Gunnar N Eastep
- the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Ruba H Ghanam
- the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Jiri Vlach
- the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Jamil S Saad
- the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Carol A Carter
- From the Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, New York 11794 and
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8
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Vlach J, Eastep GN, Ghanam RH, Watanabe SM, Carter CA, Saad JS. Structural basis for targeting avian sarcoma virus Gag polyprotein to the plasma membrane for virus assembly. J Biol Chem 2018; 293:18828-18840. [PMID: 30309983 DOI: 10.1074/jbc.ra118.003944] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Revised: 09/17/2018] [Indexed: 01/30/2023] Open
Abstract
For most retroviruses, including HIV-1, binding of the Gag polyprotein to the plasma membrane (PM) is mediated by interactions between Gag's N-terminal myristoylated matrix (MA) domain and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in the PM. The Gag protein of avian sarcoma virus (ASV) lacks the N-myristoylation signal but contains structural domains having functions similar to those of HIV-1 Gag. The molecular mechanism by which ASV Gag binds to the PM is incompletely understood. Here, we employed NMR techniques to elucidate the molecular determinants of the membrane-binding domain of ASV MA (MA87) to lipids and liposomes. We report that MA87 binds to the polar head of phosphoinositides such as PI(4,5)P2 We found that MA87 binding to inositol phosphates (IPs) is significantly enhanced by increasing the number of phosphate groups, indicating that the MA87-IP binding is governed by charge-charge interactions. Using a sensitive NMR-based liposome-binding assay, we show that binding of MA87 to liposomes is enhanced by incorporation of PI(4,5)P2 and phosphatidylserine. We also show that membrane binding is mediated by a basic surface formed by Lys-6, Lys-13, Lys-23, and Lys-24. Substitution of these residues to glutamate abolished binding of MA87 to both IPs and liposomes. In an accompanying paper, we further report that mutation of these lysine residues diminishes Gag assembly on the PM and inhibits ASV particle release. These findings provide a molecular basis for ASV Gag binding to the inner leaflet of the PM and advance our understanding of the basic mechanisms of retroviral assembly.
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Affiliation(s)
- Jiri Vlach
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294 and
| | - Gunnar N Eastep
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294 and
| | - Ruba H Ghanam
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294 and
| | - Susan M Watanabe
- the Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, New York 11794
| | - Carol A Carter
- the Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, New York 11794
| | - Jamil S Saad
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294 and
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9
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Olson ED, Musier-Forsyth K. Retroviral Gag protein-RNA interactions: Implications for specific genomic RNA packaging and virion assembly. Semin Cell Dev Biol 2018; 86:129-139. [PMID: 29580971 DOI: 10.1016/j.semcdb.2018.03.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Revised: 03/09/2018] [Accepted: 03/22/2018] [Indexed: 02/04/2023]
Abstract
Retroviral Gag proteins are responsible for coordinating many aspects of virion assembly. Gag possesses two distinct nucleic acid binding domains, matrix (MA) and nucleocapsid (NC). One of the critical functions of Gag is to specifically recognize, bind, and package the retroviral genomic RNA (gRNA) into assembling virions. Gag interactions with cellular RNAs have also been shown to regulate aspects of assembly. Recent results have shed light on the role of MA and NC domain interactions with nucleic acids, and how they jointly function to ensure packaging of the retroviral gRNA. Here, we will review the literature regarding RNA interactions with NC, MA, as well as overall mechanisms employed by Gag to interact with RNA. The discussion focuses on human immunodeficiency virus type-1, but other retroviruses will also be discussed. A model is presented combining all of the available data summarizing the various factors and layers of selection Gag employs to ensure specific gRNA packaging and correct virion assembly.
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Affiliation(s)
- Erik D Olson
- Department of Chemistry and Biochemistry, Center for RNA Biology, and Center for Retrovirus Research, Ohio State University, Columbus, OH, 43210, USA
| | - Karin Musier-Forsyth
- Department of Chemistry and Biochemistry, Center for RNA Biology, and Center for Retrovirus Research, Ohio State University, Columbus, OH, 43210, USA.
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10
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Doktorova M, Heberle FA, Kingston RL, Khelashvili G, Cuendet MA, Wen Y, Katsaras J, Feigenson GW, Vogt VM, Dick RA. Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties. Biophys J 2017; 113:2004-2015. [PMID: 29117524 DOI: 10.1016/j.bpj.2017.08.055] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Revised: 08/07/2017] [Accepted: 08/09/2017] [Indexed: 01/28/2023] Open
Abstract
Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein's matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here, using a broad set of in vitro and in silico techniques we addressed molecular mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.
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Affiliation(s)
- Milka Doktorova
- Tri-Institutional PhD Program in Computational Biology and Medicine, Weill Cornell Medical College, New York, New York
| | - Frederick A Heberle
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
| | - Richard L Kingston
- School of Biological Sciences, The University of Auckland, Auckland, New Zealand
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Michel A Cuendet
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Yi Wen
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - John Katsaras
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Gerald W Feigenson
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - Volker M Vogt
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - Robert A Dick
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York.
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11
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Doktorova M, Heberle FA, Kingston RL, Khelashvili G, Cuendet MA, Wen Y, Katsaras J, Feigenson GW, Vogt VM, Dick RA. Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties. Biophys J 2017. [PMID: 29117524 DOI: 10.1016/j.bpj.2017.08.055.] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein's matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here, using a broad set of in vitro and in silico techniques we addressed molecular mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.
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Affiliation(s)
- Milka Doktorova
- Tri-Institutional PhD Program in Computational Biology and Medicine, Weill Cornell Medical College, New York, New York
| | - Frederick A Heberle
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
| | - Richard L Kingston
- School of Biological Sciences, The University of Auckland, Auckland, New Zealand
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Michel A Cuendet
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Yi Wen
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - John Katsaras
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Gerald W Feigenson
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - Volker M Vogt
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - Robert A Dick
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York.
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12
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In vitro assembly of the Rous Sarcoma Virus capsid protein into hexamer tubes at physiological temperature. Sci Rep 2017; 7:2913. [PMID: 28588198 PMCID: PMC5460288 DOI: 10.1038/s41598-017-02060-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 04/06/2017] [Indexed: 12/21/2022] Open
Abstract
During a proteolytically-driven maturation process, the orthoretroviral capsid protein (CA) assembles to form the convex shell that surrounds the viral genome. In some orthoretroviruses, including Rous Sarcoma Virus (RSV), CA carries a short and hydrophobic spacer peptide (SP) at its C-terminus early in the maturation process, which is progressively removed as maturation proceeds. In this work, we show that RSV CA assembles in vitro at near-physiological temperatures, forming hexamer tubes that effectively model the mature capsid surface. Tube assembly is strongly influenced by electrostatic effects, and is a nucleated process that remains thermodynamically favored at lower temperatures, but is effectively arrested by the large Gibbs energy barrier associated with nucleation. RSV CA tubes are multi-layered, being formed by nested and concentric tubes of capsid hexamers. However the spacer peptide acts as a layering determinant during tube assembly. If only a minor fraction of CA-SP is present, multi-layered tube formation is blocked, and single-layered tubes predominate. This likely prevents formation of biologically aberrant multi-layered capsids in the virion. The generation of single-layered hexamer tubes facilitated 3D helical image reconstruction from cryo-electron microscopy data, revealing the basic tube architecture.
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Effects of Membrane Charge and Order on Membrane Binding of the Retroviral Structural Protein Gag. J Virol 2016; 90:9518-32. [PMID: 27512076 DOI: 10.1128/jvi.01102-16] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 08/05/2016] [Indexed: 12/28/2022] Open
Abstract
UNLABELLED The retroviral structural protein Gag binds to the inner leaflet of the plasma membrane (PM), and many cellular proteins do so as well. We used Rous sarcoma virus (RSV) Gag together with membrane sensors to study the principles governing peripheral protein membrane binding, including electrostatics, specific recognition of phospholipid headgroups, sensitivity to phospholipid acyl chain compositions, preference for membrane order, and protein multimerization. We used an in vitro liposome-pelleting assay to test protein membrane binding properties of Gag, the well-characterized MARCKS peptide, a series of fluorescent electrostatic sensor proteins (mNG-KRn), and the specific phosphatidylserine (PS) binding protein Evectin2. RSV Gag and mNG-KRn bound well to membranes with saturated and unsaturated acyl chains, whereas the MARCKS peptide and Evectin2 preferentially bound to membranes with unsaturated acyl chains. To further discriminate whether the primary driving force for Gag membrane binding is electrostatic interactions or preference for membrane order, we measured protein binding to giant unilamellar vesicles (GUVs) containing the same PS concentration in both disordered (Ld) and ordered (Lo) phases. RSV Gag and mNG-KRn membrane association followed membrane charge, independent of membrane order. Consistent with pelleting data, the MARCKS peptide showed preference for the Ld domain. Surprisingly, the PS sensor Evectin2 bound to the PS-rich Ld domain with 10-fold greater affinity than to the PS-rich Lo domain. In summary, we found that RSV Gag shows no preference for membrane order, while proteins with reported membrane-penetrating domains show preference for disordered membranes. IMPORTANCE Retroviral particles assemble on the PM and bud from infected cells. Our understanding of how Gag interacts with the PM and how different membrane properties contribute to overall Gag assembly is incomplete. This study examined how membrane charge and membrane order influence Gag membrane association. Consistent with previous work on RSV Gag, we report here that electrostatic interactions provide the primary driving force for RSV Gag membrane association. Using phase-separated GUVs with known lipid composition of the Ld and Lo phases, we demonstrate for the first time that RSV Gag is sensitive to membrane charge but not membrane order. In contrast, the cellular protein domain MARCKS and the PS sensor Evectin2 show preference for disordered membranes. We also demonstrate how to define GUV phase composition, which could serve as a tool in future studies of protein membrane interactions.
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Rye-McCurdy T, Olson ED, Liu S, Binkley C, Reyes JP, Thompson BR, Flanagan JM, Parent LJ, Musier-Forsyth K. Functional Equivalence of Retroviral MA Domains in Facilitating Psi RNA Binding Specificity by Gag. Viruses 2016; 8:v8090256. [PMID: 27657107 PMCID: PMC5035970 DOI: 10.3390/v8090256] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Revised: 09/09/2016] [Accepted: 09/12/2016] [Indexed: 12/18/2022] Open
Abstract
Retroviruses specifically package full-length, dimeric genomic RNA (gRNA) even in the presence of a vast excess of cellular RNA. The “psi” (Ψ) element within the 5′-untranslated region (5′UTR) of gRNA is critical for packaging through interaction with the nucleocapsid (NC) domain of Gag. However, in vitro Gag binding affinity for Ψ versus non-Ψ RNAs is not significantly different. Previous salt-titration binding assays revealed that human immunodeficiency virus type 1 (HIV-1) Gag bound to Ψ RNA with high specificity and relatively few charge interactions, whereas binding to non-Ψ RNA was less specific and involved more electrostatic interactions. The NC domain was critical for specific Ψ binding, but surprisingly, a Gag mutant lacking the matrix (MA) domain was less effective at discriminating Ψ from non-Ψ RNA. We now find that Rous sarcoma virus (RSV) Gag also effectively discriminates RSV Ψ from non-Ψ RNA in a MA-dependent manner. Interestingly, Gag chimeras, wherein the HIV-1 and RSV MA domains were swapped, maintained high binding specificity to cognate Ψ RNAs. Using Ψ RNA mutant constructs, determinants responsible for promoting high Gag binding specificity were identified in both systems. Taken together, these studies reveal the functional equivalence of HIV-1 and RSV MA domains in facilitating Ψ RNA selectivity by Gag, as well as Ψ elements that promote this selectivity.
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Affiliation(s)
- Tiffiny Rye-McCurdy
- Department of Chemistry and Biochemistry, The Ohio State University, Center for Retroviral Research, and Center for RNA Biology, Columbus, OH 43210, USA.
| | - Erik D Olson
- Department of Chemistry and Biochemistry, The Ohio State University, Center for Retroviral Research, and Center for RNA Biology, Columbus, OH 43210, USA.
| | - Shuohui Liu
- Department of Chemistry and Biochemistry, The Ohio State University, Center for Retroviral Research, and Center for RNA Biology, Columbus, OH 43210, USA.
| | - Christiana Binkley
- Department of Chemistry and Biochemistry, The Ohio State University, Center for Retroviral Research, and Center for RNA Biology, Columbus, OH 43210, USA.
| | - Joshua-Paolo Reyes
- Department of Chemistry and Biochemistry, The Ohio State University, Center for Retroviral Research, and Center for RNA Biology, Columbus, OH 43210, USA.
| | - Brian R Thompson
- Department of Chemistry and Biochemistry, The Ohio State University, Center for Retroviral Research, and Center for RNA Biology, Columbus, OH 43210, USA.
| | - John M Flanagan
- Department of Biochemistry and Molecular Biology, Penn State College of Medicine, Hershey, PA 17033, USA.
| | - Leslie J Parent
- Departments of Medicine and Microbiology and Immunology, Division of Infectious Diseases and Epidemiology, Penn State College of Medicine, Hershey, PA 17033, USA.
| | - Karin Musier-Forsyth
- Department of Chemistry and Biochemistry, The Ohio State University, Center for Retroviral Research, and Center for RNA Biology, Columbus, OH 43210, USA.
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Membrane Binding of the Rous Sarcoma Virus Gag Protein Is Cooperative and Dependent on the Spacer Peptide Assembly Domain. J Virol 2015; 90:2473-85. [PMID: 26676779 DOI: 10.1128/jvi.02733-15] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 12/09/2015] [Indexed: 12/28/2022] Open
Abstract
UNLABELLED The principles underlying membrane binding and assembly of retroviral Gag proteins into a lattice are understood. However, little is known about how these processes are related. Using purified Rous sarcoma virus Gag and Gag truncations, we studied the interrelation of Gag-Gag interaction and Gag-membrane interaction. Both by liposome binding and by surface plasmon resonance on a supported bilayer, Gag bound to membranes much more tightly than did matrix (MA), the isolated membrane binding domain. In principle, this difference could be explained either by protein-protein interactions leading to cooperativity in membrane binding or by the simultaneous interaction of the N-terminal MA and the C-terminal nucleocapsid (NC) of Gag with the bilayer, since both are highly basic. However, we found that NC was not required for strong membrane binding. Instead, the spacer peptide assembly domain (SPA), a putative 24-residue helical sequence comprising the 12-residue SP segment of Gag and overlapping the capsid (CA) C terminus and the NC N terminus, was required. SPA is known to be critical for proper assembly of the immature Gag lattice. A single amino acid mutation in SPA that abrogates assembly in vitro dramatically reduced binding of Gag to liposomes. In vivo, plasma membrane localization was dependent on SPA. Disulfide cross-linking based on ectopic Cys residues showed that the contacts between Gag proteins on the membrane are similar to the known contacts in virus-like particles. Taken together, we interpret these results to mean that Gag membrane interaction is cooperative in that it depends on the ability of Gag to multimerize. IMPORTANCE The retroviral structural protein Gag has three major domains. The N-terminal MA domain interacts directly with the plasma membrane (PM) of cells. The central CA domain, together with immediately adjoining sequences, facilitates the assembly of thousands of Gag molecules into a lattice. The C-terminal NC domain interacts with the genome, resulting in packaging of viral RNA. For assembly in vitro with purified Gag, in the absence of membranes, binding of NC to nucleic acid somehow facilitates further Gag-Gag interactions that lead to formation of the Gag lattice. The contributions of MA-mediated membrane binding to virus particle assembly are not well understood. Here, we report that in the absence of nucleic acid, membranes provide a platform that facilitates Gag-Gag interactions. This study demonstrates that the binding of Gag, but not of MA, to membranes is cooperative and identifies SPA as a major factor that controls this cooperativity.
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