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Umumararungu T, Nyandwi JB, Katandula J, Twizeyimana E, Claude Tomani J, Gahamanyi N, Ishimwe N, Olawode EO, Habarurema G, Mpenda M, Uyisenga JP, Saeed SI. Current status of the small molecule anti-HIV drugs in the pipeline or recently approved. Bioorg Med Chem 2024; 111:117860. [PMID: 39094527 DOI: 10.1016/j.bmc.2024.117860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2024] [Revised: 07/24/2024] [Accepted: 07/25/2024] [Indexed: 08/04/2024]
Abstract
Human Immunodeficiency Virus (HIV) is the causative agent of Acquired Immunodeficiency Syndrome (AIDS) with high morbidity and mortality rates. Treatment of AIDS/HIV is being complicated by increasing resistance to currently used antiretroviral (ARV) drugs, mainly in low- and middle-income countries (LMICs) due to drug misuse, poor drug supply and poor treatment monitoring. However, progress has been made in the development of new ARV drugs, targeting different HIV components (Fig. 1). This review aims at presenting and discussing the progress made towards the discovery of new ARVs that are at different stages of clinical trials as of July 2024. For each compound, the mechanism of action, target biomolecule, genes associated with resistance, efficacy and safety, class, and phase of clinical trial are discussed. These compounds include analogues of nucleoside reverse transcriptase inhibitors (NRTIs) - islatravir and censavudine; non-nucleoside reverse transcriptase inhibitors (NNRTIs) - Rilpivirine, elsulfavirine and doravirine; integrase inhibitors namely cabotegravir and dolutegravir and chemokine coreceptors 5 and 2 (CC5/CCR2) antagonists for example cenicriviroc. Also, fostemsavir is being developed as an attachment inhibitor while lenacapavir, VH4004280 and VH4011499 are capsid inhibitors. Others are maturation inhibitors such as GSK-254, GSK3532795, GSK3739937, GSK2838232, and other compounds labelled as miscellaneous (do not belong to the classical groups of anti-HIV drugs or to the newer classes) such as obefazimod and BIT225. There is a considerable progress in the development of new anti-HIV drugs and the effort will continue since HIV infections has no cure or vaccine till now. Efforts are needed to reduce the toxicity of available drugs or discover new drugs with new classes which can delay the development of resistance.
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Affiliation(s)
- Théoneste Umumararungu
- Department of Industrial Pharmacy, School of Medicine and Pharmacy, College of Medicine and Health Sciences, University of Rwanda, Rwanda.
| | - Jean Baptiste Nyandwi
- Department of Pharmacology and Toxicology, School of Medicine and Pharmacy, College of Medicine and Health Sciences, University of Rwanda, Rwanda; East African Community Regional Centre of Excellence for Vaccines, Immunization and Health Supply Chain Management, Kigali, Rwanda
| | - Jonathan Katandula
- Department of Pharmacology and Toxicology, School of Medicine and Pharmacy, College of Medicine and Health Sciences, University of Rwanda, Rwanda
| | - Eric Twizeyimana
- Department of Physiology, School of Medicine and Pharmacy, College of Medicine and Health Sciences, University of Rwanda, Rwanda
| | - Jean Claude Tomani
- Department of Chemistry, School of Science, College of Science and Technology, University of Rwanda, Rwanda
| | - Noël Gahamanyi
- Department of Biology, School of Science, College of Science and Technology, University of Rwanda, Rwanda
| | - Nestor Ishimwe
- Vascular Biology Center, Medical College of Georgia at Augusta University, Augusta, GA, USA
| | - Emmanuel Oladayo Olawode
- Department of Pharmaceutical Sciences, College of Pharmacy, Larkin University, 18301 N Miami Ave #1, Miami, FL 33169, USA
| | - Gratien Habarurema
- Department of Chemistry, School of Science, College of Science and Technology, University of Rwanda, Rwanda
| | - Matabishi Mpenda
- Department of Pharmacology and Toxicology, School of Medicine and Pharmacy, College of Medicine and Health Sciences, University of Rwanda, Rwanda
| | - Jeanne Primitive Uyisenga
- Department of Biology, School of Science, College of Science and Technology, University of Rwanda, Rwanda
| | - Shamsaldeen Ibrahim Saeed
- Faculty of Veterinary Science, University of Nyala, P.O. Box: 155, Nyala, Sudan; Nanotechnology in Veterinary Medicine (NanoVet) Research Group, Faculty of Veterinary Medicine, University Malaysia Kelantan, Kelantan 16100, Pengkalan Chepa, Malaysia
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Gruenke P, Mayer MD, Aneja R, Schulze WJ, Song Z, Burke DH, Heng X, Lange MJ. A Branched SELEX Approach Identifies RNA Aptamers That Bind Distinct HIV-1 Capsid Structural Components. ACS Infect Dis 2024; 10:2637-2655. [PMID: 39016538 PMCID: PMC11320578 DOI: 10.1021/acsinfecdis.3c00708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 07/09/2024] [Accepted: 07/10/2024] [Indexed: 07/18/2024]
Abstract
The HIV-1 capsid protein (CA) assumes distinct structural forms during replication, each presenting unique, solvent-accessible surfaces that facilitate multifaceted functions and host factor interactions. However, functional contributions of individual CA structures remain unclear, as evaluation of CA presents several technical challenges. To address this knowledge gap, we identified CA-targeting aptamers with different structural specificities, which emerged through a branched SELEX approach using an aptamer library previously selected to bind the CA hexamer lattice. Subsets were either highly specific for the CA lattice or bound both the CA lattice and CA hexamer. We then evaluated four representatives to reveal aptamer regions required for binding, highlighting interesting structural features and challenges in aptamer structure determination. Further, we demonstrate binding to biologically relevant CA structural forms and aptamer-mediated affinity purification of CA from cell lysates without virus or host modification, supporting the development of structural form-specific aptamers as exciting new tools for the study of CA.
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Affiliation(s)
- Paige
R. Gruenke
- Department
of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri 65212, United States
- Department
of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
- Bond
Life Sciences Center, University of Missouri, Columbia, Missouri 65211, United States
| | - Miles D. Mayer
- Department
of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Rachna Aneja
- Department
of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri 65212, United States
| | - William J. Schulze
- Department
of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri 65212, United States
| | - Zhenwei Song
- Department
of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Donald H. Burke
- Department
of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri 65212, United States
- Department
of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
- Bond
Life Sciences Center, University of Missouri, Columbia, Missouri 65211, United States
| | - Xiao Heng
- Department
of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Margaret J. Lange
- Department
of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri 65212, United States
- Department
of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
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3
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Gruenke PR, Mayer MD, Aneja R, Song Z, Burke DH, Heng X, Lange MJ. Differentiation SELEX approach identifies RNA aptamers with different specificities for HIV-1 capsid assembly forms. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.11.571135. [PMID: 38168417 PMCID: PMC10760009 DOI: 10.1101/2023.12.11.571135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
The HIV-1 capsid protein (CA) assumes distinct assembly forms during replication, each presenting unique, solvent-accessible surfaces that facilitate multifaceted functions and host factor interactions. However, contributions of individual CA assemblies remain unclear, as the evaluation of CA in cells presents several technical challenges. To address this need, we sought to identify CA assembly form-specific aptamers. Aptamer subsets with different specificities emerged from within a highly converged, pre-enriched aptamer library previously selected to bind the CA hexamer lattice. Subsets were either highly specific for CA lattice or bound both CA lattice and CA hexamer. We further evaluated four representatives to reveal aptamer structural features required for binding, highlighting interesting features and challenges in aptamer structure determination. Importantly, our aptamers bind biologically relevant forms of CA and we demonstrate aptamer-mediated affinity purification of CA from cell lysates without virus or host modification. Thus, we have identified CA assembly form-specific aptamers that represent exciting new tools for the study of CA.
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Zhang MJ, Stear JH, Jacques DA, Böcking T. Insights into HIV uncoating from single-particle imaging techniques. Biophys Rev 2022; 14:23-32. [PMID: 35340594 PMCID: PMC8921429 DOI: 10.1007/s12551-021-00922-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Accepted: 11/23/2021] [Indexed: 01/13/2023] Open
Abstract
Human immunodeficiency virus (HIV) is the most extensively researched human pathogen. Despite this massive scientific endeavour, several fundamental viral processes remain enigmatic. One such critical process is uncoating-the event that releases the viral genome from the proteinaceous shell of the capsid during infection. While this process is conceptually simple, the molecular underpinnings, timing, regulation, and cellular location of uncoating remain contentious. This review describes the hurdles that have limited our understanding in this area and presents recently deployed in vitro and in cellulo techniques that have been developed expressly with the aim of directly visualising capsid uncoating at the single-particle level and understanding the mechanics behind this essential aspect of HIV infection.
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Affiliation(s)
- Margaret J. Zhang
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences, University of New South Wales, Sydney, NSW 2052 Australia
| | - Jeffrey H. Stear
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences, University of New South Wales, Sydney, NSW 2052 Australia
| | - David A. Jacques
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences, University of New South Wales, Sydney, NSW 2052 Australia
| | - Till Böcking
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences, University of New South Wales, Sydney, NSW 2052 Australia
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Gruenke PR, Aneja R, Welbourn S, Ukah OB, Sarafianos SG, Burke DH, Lange MJ. Selection and identification of an RNA aptamer that specifically binds the HIV-1 capsid lattice and inhibits viral replication. Nucleic Acids Res 2022; 50:1701-1717. [PMID: 35018437 PMCID: PMC8860611 DOI: 10.1093/nar/gkab1293] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Revised: 11/23/2021] [Accepted: 12/16/2021] [Indexed: 01/25/2023] Open
Abstract
The HIV-1 capsid core participates in several replication processes. The mature capsid core is a lattice composed of capsid (CA) monomers thought to assemble first into CA dimers, then into ∼250 CA hexamers and 12 CA pentamers. CA assembly requires conformational flexibility of each unit, resulting in the presence of unique, solvent-accessible surfaces. Significant advances have improved our understanding of the roles of the capsid core in replication; however, the contributions of individual CA assembly forms remain unclear and there are limited tools available to evaluate these forms in vivo. Here, we have selected aptamers that bind CA lattice tubes. We describe aptamer CA15-2, which selectively binds CA lattice, but not CA monomer or CA hexamer, suggesting that it targets an interface present and accessible only on CA lattice. CA15-2 does not compete with PF74 for binding, indicating that it likely binds a non-overlapping site. Furthermore, CA15-2 inhibits HIV-1 replication when expressed in virus producer cells, but not target cells, suggesting that it binds a biologically-relevant site during virus production that is either not accessible during post-entry replication steps or is accessible but unaltered by aptamer binding. Importantly, CA15-2 represents the first aptamer that specifically recognizes the HIV-1 CA lattice.
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Affiliation(s)
- Paige R Gruenke
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA.,Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA
| | - Rachna Aneja
- Department of Molecular Microbiology & Immunology, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Sarah Welbourn
- Emory Vaccine Center and Yerkes National Primate Research Center, Emory University, Atlanta, GA 30329, USA
| | - Obiaara B Ukah
- Department of Molecular Microbiology & Immunology, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Stefan G Sarafianos
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Donald H Burke
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA.,Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA.,Department of Molecular Microbiology & Immunology, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Margaret J Lange
- Department of Molecular Microbiology & Immunology, School of Medicine, University of Missouri, Columbia, MO 65211, USA
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McFadden WM, Snyder AA, Kirby KA, Tedbury PR, Raj M, Wang Z, Sarafianos SG. Rotten to the core: antivirals targeting the HIV-1 capsid core. Retrovirology 2021; 18:41. [PMID: 34937567 PMCID: PMC8693499 DOI: 10.1186/s12977-021-00583-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 11/09/2021] [Indexed: 12/20/2022] Open
Abstract
The capsid core of HIV-1 is a large macromolecular assembly that surrounds the viral genome and is an essential component of the infectious virus. In addition to its multiple roles throughout the viral life cycle, the capsid interacts with multiple host factors. Owing to its indispensable nature, the HIV-1 capsid has been the target of numerous antiretrovirals, though most capsid-targeting molecules have not had clinical success until recently. Lenacapavir, a long-acting drug that targets the HIV-1 capsid, is currently undergoing phase 2/3 clinical trials, making it the most successful capsid inhibitor to-date. In this review, we detail the role of the HIV-1 capsid protein in the virus life cycle, categorize antiviral compounds based on their targeting of five sites within the HIV-1 capsid, and discuss their molecular interactions and mechanisms of action. The diverse range of inhibition mechanisms provides insight into possible new strategies for designing novel HIV-1 drugs and furthers our understanding of HIV-1 biology. ![]()
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Affiliation(s)
- William M McFadden
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - Alexa A Snyder
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - Karen A Kirby
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, 30322, USA.,Children's Healthcare of Atlanta, Atlanta, GA, 30322, USA
| | - Philip R Tedbury
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, 30322, USA.,Children's Healthcare of Atlanta, Atlanta, GA, 30322, USA
| | - Monika Raj
- Department of Chemistry, Emory University, Atlanta, GA, 30322, USA
| | - Zhengqiang Wang
- Center for Drug Design, College of Pharmacy, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Stefan G Sarafianos
- Laboratory of Biochemical Pharmacology, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, 30322, USA. .,Children's Healthcare of Atlanta, Atlanta, GA, 30322, USA.
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7
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Saito A, Yamashita M. HIV-1 capsid variability: viral exploitation and evasion of capsid-binding molecules. Retrovirology 2021; 18:32. [PMID: 34702294 PMCID: PMC8549334 DOI: 10.1186/s12977-021-00577-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 10/13/2021] [Indexed: 11/17/2022] Open
Abstract
The HIV-1 capsid, a conical shell encasing viral nucleoprotein complexes, is involved in multiple post-entry processes during viral replication. Many host factors can directly bind to the HIV-1 capsid protein (CA) and either promote or prevent HIV-1 infection. The viral capsid is currently being explored as a novel target for therapeutic interventions. In the past few decades, significant progress has been made in our understanding of the capsid–host interactions and mechanisms of action of capsid-targeting antivirals. At the same time, a large number of different viral capsids, which derive from many HIV-1 mutants, naturally occurring variants, or diverse lentiviruses, have been characterized for their interactions with capsid-binding molecules in great detail utilizing various experimental techniques. This review provides an overview of how sequence variation in CA influences phenotypic properties of HIV-1. We will focus on sequence differences that alter capsid–host interactions and give a brief account of drug resistant mutations in CA and their mutational effects on viral phenotypes. Increased knowledge of the sequence-function relationship of CA helps us deepen our understanding of the adaptive potential of the viral capsid.
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Affiliation(s)
- Akatsuki Saito
- Department of Veterinary Medicine, Faculty of Agriculture, University of Miyazaki, Miyazaki, Miyazaki, Japan.,Center for Animal Disease Control, University of Miyazaki, Miyazaki, Miyazaki, Japan
| | - Masahiro Yamashita
- Aaron Diamond AIDS Research Center, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA.
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8
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Thames T, J Bryer A, Qiao X, Jeon J, Weed R, Janicki K, Hu B, Gor’kov PL, Hung I, Gan Z, Perilla JR, Chen B. Curvature of the Retroviral Capsid Assembly Is Modulated by a Molecular Switch. J Phys Chem Lett 2021; 12:7768-7776. [PMID: 34374542 PMCID: PMC9083439 DOI: 10.1021/acs.jpclett.1c01769] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
During the maturation step, the retroviral capsid proteins (CAs) assemble into polymorphic capsids. Their acute curvature is largely determined by 12 pentamers inserted into the hexameric lattice. However, how the CA switches its conformation to control assembly curvature remains unclear. We report the high-resolution structural model of the Rous sarcoma virus (RSV) CA T = 1 capsid, established by molecular dynamics simulations combining solid-state NMR and prior cryoelectron tomography restraints. Comparing this with our previous model of the RSV CA tubular assembly, we identify the key residues for dictating the incorporation of acute curvatures. These residues undergo large torsion angle changes, resulting in a 34° rotation of the C-terminal domain relative to its N-terminal domain around the flexible interdomain linker, without substantial changes of either the conformation of individual domains or the assembly contact interfaces. This knowledge provides new insights to help decipher the mechanism of the retroviral capsid assembly.
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Affiliation(s)
- Tyrone Thames
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
| | - Alexander J Bryer
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
| | - Xin Qiao
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
| | - Jaekyun Jeon
- Laboratory of Chemical Physics, NIDDK, NIH, Bethesda, MD 20892, USA
| | - Ryan Weed
- Department of Chemistry, University of Central Florida, Orlando, FL 32816, USA
| | - Kaylie Janicki
- Department of Chemistry, University of Central Florida, Orlando, FL 32816, USA
| | - Bingwen Hu
- State Key Laboratory of Precision Spectroscopy, Shanghai Key Laboratory of Magnetic Resonance, Institute of Functional Materials, School of Physics and Materials Science, East China Normal University, Shanghai 200062, PR China
| | - Peter L. Gor’kov
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Ivan Hung
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Zhehong Gan
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Juan R Perilla
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
| | - Bo Chen
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
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Allosteric Regulation of HIV-1 Capsid Structure for Gag Assembly, Virion Production, and Viral Infectivity by a Disordered Interdomain Linker. J Virol 2019; 93:JVI.00381-19. [PMID: 31189701 DOI: 10.1128/jvi.00381-19] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2019] [Accepted: 06/04/2019] [Indexed: 12/12/2022] Open
Abstract
The retroviral Gag capsid (Gag-CA) interdomain linker is an unstructured peptide segment connecting structured N-terminal and C-terminal domains. Although the region is reported to play roles in virion morphogenesis and infectivity, underlying molecular mechanisms remain unexplored. To address this issue, we determined biological and molecular phenotypes of HIV-1 CA linker mutants by experimental and in silico approaches. Among the nine linker mutants tested, eight exhibited attenuation of viral particle production to various extents mostly in parallel with a reduction in viral infectivity. Sucrose density gradient, confocal microscopy, and live-cell protein interaction analyses indicated that the defect is accompanied by attenuation of Gag-Gag interactions following Gag plasma membrane targeting in the cells. In silico analyses revealed distinct distributions of interaction-prone hydrophobic patches between immature and mature CA proteins. Molecular dynamics simulations predicted that the linker mutations can allosterically alter structural fluctuations, including the interaction surfaces apart from the mutation sites in both the immature and mature CA proteins. These results suggest that the HIV-1 CA interdomain linker is a cis-modulator of the CA interaction surfaces to optimize efficiency of Gag assembly, virion production, and viral infectivity.IMPORTANCE HIV-1 particle production and infection are highly ordered processes. Viral Gag proteins play a central role in the assembly and disassembly of viral molecules. Of these, capsid protein (CA) is a major contributor to the Gag-Gag interactions. CA consists of two structured domains, i.e., N-terminal (NTD) and C-terminal (CTD) domains, connected by an unstructured domain named the interdomain linker. While multiple regions in the NTD and CTD are reported to play roles in virion morphogenesis and infectivity, the roles of the linker region in Gag assembly and virus particle formation remain elusive. In this study, we showed by biological and molecular analyses that the linker region functions as an intramolecular modulator to tune Gag assembly, virion production, and viral infectivity. Our study thus illustrates a hitherto-unrecognized mechanism, an allosteric regulation of CA structure by the disordered protein element, for HIV-1 replication.
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Doi N, Koma T, Adachi A, Nomaguchi M. Role for Gag-CA Interdomain Linker in Primate Lentiviral Replication. Front Microbiol 2019; 10:1831. [PMID: 31440231 PMCID: PMC6694209 DOI: 10.3389/fmicb.2019.01831] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Accepted: 07/25/2019] [Indexed: 11/13/2022] Open
Abstract
Gag proteins underlie retroviral replication by fulfilling numerous functional roles at various stages during viral life cycle. Out of the four mature proteins, Gag-capsid (CA) is a major component of viral particles, and has been most well studied biogenetically, biochemically and structurally. Gag-CA is composed of two structured domains, and also of a short stretch of disordered and flexible interdomain linker. While the two domains, namely, N-terminal and C-terminal domains (NTD and CTD), have been the central target for Gag research, the linker region connecting the two has been poorly studied. We recently have performed systemic mutational analyses on the Gag-CA linker region of HIV-1 by various experimental and in silico systems. In total, we have demonstrated that the linker region acts as a cis-modulator to optimize the Gag-related viral replication process. We also have noted, during the course of conducting the research project, that HIV-1 and SIVmac, belonging to distinct primate lentiviral lineages, share a similarly biologically active linker region with each other. In this brief article, we summarize and report the results obtained by mutational studies that are relevant to the functional significance of the interdomain linker of HIV/SIV Gag-CA. Based on this investigation, we discuss about the future directions of the research in this line.
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Affiliation(s)
- Naoya Doi
- Department of Microbiology, Graduate School of Medical Science, Tokushima University, Tokushima, Japan
| | - Takaaki Koma
- Department of Microbiology, Graduate School of Medical Science, Tokushima University, Tokushima, Japan
| | - Akio Adachi
- Department of Microbiology, Kansai Medical University, Osaka, Japan
| | - Masako Nomaguchi
- Department of Microbiology, Graduate School of Medical Science, Tokushima University, Tokushima, Japan
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11
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Broniarczyk J, Massimi P, Pim D, Bergant Marušič M, Myers MP, Garcea RL, Banks L. Phosphorylation of Human Papillomavirus Type 16 L2 Contributes to Efficient Virus Infectious Entry. J Virol 2019; 93:e00128-19. [PMID: 30996086 PMCID: PMC6580975 DOI: 10.1128/jvi.00128-19] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Accepted: 04/05/2019] [Indexed: 01/10/2023] Open
Abstract
The human papillomavirus (HPV) capsid comprises two viral proteins, L1 and L2, with the L2 component being essential to ensure efficient endocytic transport of incoming viral genomes. Several studies have previously reported that L1 and L2 are posttranslationally modified, but it is uncertain whether these modifications affect HPV infectious entry. Using a proteomic screen, we identified a highly conserved phospho-acceptor site on the HPV-16 and bovine papillomavirus 1 (BPV-1) L2 proteins. The phospho-modification of L2 and its presence in HPV pseudovirions (PsVs) were confirmed using anti-phospho-L2-specific antibodies. Mutation of the phospho-acceptor sites of both HPV-16 and BPV-1 L2 resulted in the production of infectious virus particles, with no differences in efficiencies of packaging the reporter DNA. However, these mutated PsVs showed marked defects in infectious entry. Further analysis revealed a defect in uncoating, characterized by a delay in the exposure of a conformational epitope on L1 that indicates capsid uncoating. This uncoating defect was accompanied by a delay in the proteolysis of both L1 and L2 in mutated HPV-16 PsVs. Taken together, these studies indicate that phosphorylation of L2 during virus assembly plays an important role in optimal uncoating of virions during infection, suggesting that phosphorylation of the viral capsid proteins contributes to infectious entry.IMPORTANCE The papillomavirus L2 capsid protein plays an essential role in infectious entry, where it directs the successful trafficking of incoming viral genomes to the nucleus. However, nothing is known about how potential posttranslational modifications may affect different aspects of capsid assembly or infectious entry. In this study, we report the first phospho-specific modification of the BPV-1 and HPV-16 L2 capsid proteins. The phospho-acceptor site is very highly conserved across multiple papillomavirus types, indicating a highly conserved function within the L2 protein and the viral capsid. We show that this modification plays an essential role in infectious entry, where it modulates susceptibility of the incoming virus to capsid disassembly. These studies therefore define a completely new means of regulating the papillomavirus L2 proteins, a regulation that optimizes endocytic processing and subsequent completion of the infectious entry pathway.
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Affiliation(s)
- Justyna Broniarczyk
- Tumour Virology Laboratory, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
- Department of Molecular Virology, Adam Mickiewicz University, Poznan, Poland
| | - Paola Massimi
- Tumour Virology Laboratory, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
| | - David Pim
- Tumour Virology Laboratory, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
| | - Martina Bergant Marušič
- Laboratory for Environmental and Life Sciences, University of Nova Gorica, Nova Gorica, Slovenia
| | - Michael P Myers
- Protein Networks, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
| | - Robert L Garcea
- BioFrontiers Institute and the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado, USA
| | - Lawrence Banks
- Tumour Virology Laboratory, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
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12
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Latinovic OS, Reitz M, Heredia A. CCR5 Inhibitors and HIV-1 Infection. JOURNAL OF AIDS AND HIV TREATMENT 2019; 1:1-5. [PMID: 31414081 PMCID: PMC6693856 DOI: 10.33696/aids.1.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Olga S. Latinovic
- Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Marvin Reitz
- Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Alonso Heredia
- Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA
- School of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, USA
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13
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Quinn CM, Wang M, Fritz MP, Runge B, Ahn J, Xu C, Perilla JR, Gronenborn AM, Polenova T. Dynamic regulation of HIV-1 capsid interaction with the restriction factor TRIM5α identified by magic-angle spinning NMR and molecular dynamics simulations. Proc Natl Acad Sci U S A 2018; 115:11519-11524. [PMID: 30333189 PMCID: PMC6233135 DOI: 10.1073/pnas.1800796115] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The host factor protein TRIM5α plays an important role in restricting the host range of HIV-1, interfering with the integrity of the HIV-1 capsid. TRIM5 triggers an antiviral innate immune response by functioning as a capsid pattern recognition receptor, although the precise mechanism by which the restriction is imposed is not completely understood. Here we used an integrated magic-angle spinning nuclear magnetic resonance and molecular dynamics simulations approach to characterize, at atomic resolution, the dynamics of the capsid's hexameric and pentameric building blocks, and the interactions with TRIM5α in the assembled capsid. Our data indicate that assemblies in the presence of the pentameric subunits are more rigid on the microsecond to millisecond timescales than tubes containing only hexamers. This feature may be of key importance for controlling the capsid's morphology and stability. In addition, we found that TRIM5α binding to capsid induces global rigidification and perturbs key intermolecular interfaces essential for higher-order capsid assembly, with structural and dynamic changes occurring throughout the entire CA polypeptide chain in the assembly, rather than being limited to a specific protein-protein interface. Taken together, our results suggest that TRIM5α uses several mechanisms to destabilize the capsid lattice, ultimately inducing its disassembly. Our findings add to a growing body of work indicating that dynamic allostery plays a pivotal role in capsid assembly and HIV-1 infectivity.
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Affiliation(s)
- Caitlin M Quinn
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh, Pittsburgh, PA 15260
| | - Mingzhang Wang
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh, Pittsburgh, PA 15260
| | - Matthew P Fritz
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh, Pittsburgh, PA 15260
| | - Brent Runge
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh, Pittsburgh, PA 15260
| | - Jinwoo Ahn
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh, Pittsburgh, PA 15260
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260
| | - Chaoyi Xu
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716
| | - Juan R Perilla
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716;
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh, Pittsburgh, PA 15260
| | - Angela M Gronenborn
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh, Pittsburgh, PA 15260;
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260
| | - Tatyana Polenova
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716;
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh, Pittsburgh, PA 15260
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14
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Phosphorylation of the HIV-1 capsid by MELK triggers uncoating to promote viral cDNA synthesis. PLoS Pathog 2017; 13:e1006441. [PMID: 28683086 PMCID: PMC5500366 DOI: 10.1371/journal.ppat.1006441] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 06/02/2017] [Indexed: 11/19/2022] Open
Abstract
Regulation of capsid disassembly is crucial for efficient HIV-1 cDNA synthesis after entry, yet host factors involved in this process remain largely unknown. Here, we employ genetic screening of human T-cells to identify maternal embryonic leucine zipper kinase (MELK) as a host factor required for optimal uncoating of the HIV-1 core to promote viral cDNA synthesis. Depletion of MELK inhibited HIV-1 cDNA synthesis with a concomitant delay of capsid disassembly. MELK phosphorylated Ser-149 of the capsid in the multimerized HIV-1 core, and a mutant virus carrying a phosphorylation-mimetic amino-acid substitution of Ser-149 underwent premature capsid disassembly and earlier HIV-1 cDNA synthesis, and eventually failed to enter the nucleus. Moreover, a small-molecule MELK inhibitor reduced the efficiency of HIV-1 replication in peripheral blood mononuclear cells in a dose-dependent manner. These results reveal a previously unrecognized mechanism of HIV-1 capsid disassembly and implicate MELK as a potential target for anti-HIV therapy. Phosphorylation of the HIV-1 capsid has long been known to regulate viral uncoating and cDNA synthesis processes, but the cellular kinases responsible for this have remained unidentified. Here, we report that a host cell kinase MELK dictates optimal capsid disassembly through phosphorylation of Ser-149 in the multimerized HIV-1 core, which leads to efficient viral cDNA synthesis in target cells. The phosphorylation-mimetic capsid mutation of Ser-149 caused aberrant capsid disassembly and too-early completion of reverse transcription, and impeded nuclear entry of HIV-1 cDNA, suggesting the importance of well-ordered capsid disassembly in the early stages of viral replication. This discovery will facilitate understanding of the functional link among virus uncoating, reverse transcription and nuclear entry, and is expected to contribute to developing a novel strategy for AIDS therapy.
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15
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Thenin-Houssier S, Valente ST. HIV-1 Capsid Inhibitors as Antiretroviral Agents. Curr HIV Res 2016; 14:270-82. [PMID: 26957201 DOI: 10.2174/1570162x14999160224103555] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 08/12/2015] [Accepted: 09/01/2015] [Indexed: 01/09/2023]
Abstract
BACKGROUND The infectious human immunodeficiency virus (HIV) particle is characterized by a conical capsid that encloses the viral RNA genome. The capsid is essential for HIV-1 replication and plays crucial roles in both early and late stages of the viral life cycle. Early on, upon fusion of the viral and cellular membranes, the viral capsid is released into the host cell cytoplasm and dissociates in a process known as uncoating, tightly associated with the reverse transcription of the viral genome. During the late stages of viral replication, the Gag polyprotein, precursor of the capsid protein, assemble at the plasma membrane to form immature non-infectious viral particles. After a maturation step by the viral protease, the capsid assembles to form a fullerene-like conical shape characteristic of the mature infectious particle. Mutations affecting the uncoating process, or capsid assembly and maturation, have been shown to hamper viral infectivity. The key role of capsid in viral replication and the absence of approved drugs against this protein have promoted the development of antiretrovirals. Screening based on the inhibition of capsid assembly and virtual screening for molecules binding to the capsid have successfully identified a number of potential small molecule compounds. Unfortunately, none of these molecules is currently used in the clinic. CONCLUSION Here we review the discovery and the mechanism of action of the small molecules and peptides identified as capsid inhibitors, and discuss their therapeutic potential.
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Affiliation(s)
| | - Susana T Valente
- Department Immunology and Microbial Sciences, The Scripps Research Institute, 130 Scripps Way, 3C1, Jupiter, FL 33458, USA.
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16
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Bergman S, Lezon TR. Modeling global changes induced by local perturbations to the HIV-1 capsid. J Mol Graph Model 2016; 71:218-226. [PMID: 27951510 DOI: 10.1016/j.jmgm.2016.12.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 11/04/2016] [Accepted: 12/01/2016] [Indexed: 02/02/2023]
Abstract
The HIV-1 capsid is a conical protein shell made up of hexamers and pentamers of the capsid protein. The capsid houses the viral genome and replication machinery, and its opening, or uncoating, within the host cell marks a critical step in the HIV-1 lifecycle. Binding of host factors such as TRIM5α and cyclophilin A (CypA) can alter the capsid's stability, accelerating or delaying the onset of uncoating and disrupting infectivity. We employ coarse-grained computational modeling to investigate the effects of point mutations and host factor binding on HIV-1 capsid stability. We find that the largest fluctuations occur in the low-curvature regions of the capsid, and that its structural dynamics are affected by perturbations at the inter-hexamer interfaces and near the CypA binding loop, suggesting roles for these features in capsid stability. Our models show that linking capsid proteins across hexamers attenuates vibration in the low-curvature regions of the capsid, but that linking within hexamers does not. These results indicate a possible mechanism through which CypA binding alters capsid stability and highlight the utility of coarse-grained network modeling for understanding capsid mechanics.
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Affiliation(s)
- Shana Bergman
- Department of Computational and Systems Biology, University of Pittsburgh, Suite 3064 Biomedical Science Tower 3, 3501 Fifth Avenue, Pittsburgh, PA 15260, USA.
| | - Timothy R Lezon
- Department of Computational and Systems Biology, University of Pittsburgh, Suite 3064 Biomedical Science Tower 3, 3501 Fifth Avenue, Pittsburgh, PA 15260, USA; University of Pittsburgh Drug Discovery Institute, University of Pittsburgh, W965 Biomedical Science Tower, 200 Lothrop Street, Pittsburgh, PA 15261, USA.
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17
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Gres AT, Kirby KA, KewalRamani VN, Tanner JJ, Pornillos O, Sarafianos SG. STRUCTURAL VIROLOGY. X-ray crystal structures of native HIV-1 capsid protein reveal conformational variability. Science 2015; 349:99-103. [PMID: 26044298 DOI: 10.1126/science.aaa5936] [Citation(s) in RCA: 181] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 05/27/2015] [Indexed: 12/19/2022]
Abstract
The detailed molecular interactions between native HIV-1 capsid protein (CA) hexamers that shield the viral genome and proteins have been elusive. We report crystal structures describing interactions between CA monomers related by sixfold symmetry within hexamers (intrahexamer) and threefold and twofold symmetry between neighboring hexamers (interhexamer). The structures describe how CA builds hexagonal lattices, the foundation of mature capsids. Lattice structure depends on an adaptable hydration layer modulating interactions among CA molecules. Disruption of this layer alters interhexamer interfaces, highlighting an inherent structural variability. A CA-targeting antiviral affects capsid stability by binding across CA molecules and subtly altering interhexamer interfaces remote to the ligand-binding site. Inherent structural plasticity, hydration layer rearrangement, and effector binding affect capsid stability and have functional implications for the retroviral life cycle.
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Affiliation(s)
- Anna T Gres
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA. Department of Chemistry, University of Missouri, Columbia, MO 65211, USA
| | - Karen A Kirby
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA. Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine, Columbia, MO 65211, USA
| | - Vineet N KewalRamani
- Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA
| | - John J Tanner
- Department of Chemistry, University of Missouri, Columbia, MO 65211, USA. Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
| | - Owen Pornillos
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Stefan G Sarafianos
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA. Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine, Columbia, MO 65211, USA. Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA.
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18
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Le Sage V, Mouland AJ, Valiente-Echeverría F. Roles of HIV-1 capsid in viral replication and immune evasion. Virus Res 2014; 193:116-29. [PMID: 25036886 DOI: 10.1016/j.virusres.2014.07.010] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 07/04/2014] [Accepted: 07/07/2014] [Indexed: 02/07/2023]
Abstract
The primary roles of the human immunodeficiency virus type 1 (HIV-1) capsid (CA) protein are to encapsidate and protect the viral RNA genome. It is becoming increasing apparent that HIV-1 CA is a multifunctional protein that acts early during infection to coordinate uncoating, reverse transcription, nuclear import of the pre-integration complex and integration of double stranded viral DNA into the host genome. Additionally, numerous recent studies indicate that CA is playing a crucial function in HIV-1 immune evasion. Here we summarize the current knowledge on HIV-1 CA and its interactions with the host cell to promote infection. The fact that CA engages in a number of different protein-protein interactions with the host makes it an interesting target for the development of new potent antiviral agents.
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Affiliation(s)
- Valerie Le Sage
- HIV-1 RNA Trafficking Laboratory, Lady Davis Institute, Jewish General Hospital, Montréal, Québec H3T1E2, Canada; Department of Medicine, Division of Experimental Medicine, McGill University, Montréal, Québec H3A 1A3, Canada
| | - Andrew J Mouland
- HIV-1 RNA Trafficking Laboratory, Lady Davis Institute, Jewish General Hospital, Montréal, Québec H3T1E2, Canada; Department of Medicine, Division of Experimental Medicine, McGill University, Montréal, Québec H3A 1A3, Canada; Department of Microbiology and Immunology, McGill University, Montréal, Québec, H3A2B4, Canada
| | - Fernando Valiente-Echeverría
- HIV-1 RNA Trafficking Laboratory, Lady Davis Institute, Jewish General Hospital, Montréal, Québec H3T1E2, Canada; Department of Medicine, Division of Experimental Medicine, McGill University, Montréal, Québec H3A 1A3, Canada.
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19
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Ambrose Z, Aiken C. HIV-1 uncoating: connection to nuclear entry and regulation by host proteins. Virology 2014; 454-455:371-9. [PMID: 24559861 DOI: 10.1016/j.virol.2014.02.004] [Citation(s) in RCA: 124] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 12/27/2013] [Accepted: 02/04/2014] [Indexed: 11/25/2022]
Abstract
The RNA genome of human immunodeficiency virus type 1 (HIV-1) is enclosed by a capsid shell that dissociates within the cell in a multistep process known as uncoating, which influences completion of reverse transcription of the viral genome. Double-stranded viral DNA is imported into the nucleus for integration into the host genome, a hallmark of retroviral infection. Reverse transcription, nuclear entry, and integration are coordinated by a capsid uncoating process that is regulated by cellular proteins. Although uncoating is not well understood, recent studies have revealed insights into the process, particularly with respect to nuclear import pathways and protection of the viral genome from DNA sensors. Understanding uncoating will be valuable toward developing novel antiretroviral therapies for HIV-infected individuals.
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Affiliation(s)
- Zandrea Ambrose
- Division of Infectious Diseases, Department of Medicine, University of Pittsburgh, School of Medicine, Pittsburgh, PA 15261, USA.
| | - Christopher Aiken
- Department of Pathology, Microbiology and Immunology, Vanderbilt University, School of Medicine, Nashville, TN 37232, USA
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20
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Kono K, Takeda E, Tsutsui H, Kuroishi A, Hulme AE, Hope TJ, Nakayama EE, Shioda T. Slower uncoating is associated with impaired replicative capability of simian-tropic HIV-1. PLoS One 2013; 8:e72531. [PMID: 23967315 PMCID: PMC3742594 DOI: 10.1371/journal.pone.0072531] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2013] [Accepted: 07/10/2013] [Indexed: 11/19/2022] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1) productively infects only humans and chimpanzees, but not Old World monkeys, such as rhesus and cynomolgus (CM) monkeys. To establish a monkey model of HIV-1/AIDS, several HIV-1 derivatives have been constructed. We previously generated a simian-tropic HIV-1 that replicates efficiently in CM cells. This virus encodes a capsid protein (CA) with SIVmac239-derived loops between α-helices 4 and 5 (L4/5) and between α-helices 6 and 7 (L6/7), along with the entire vif from SIVmac239 (NL-4/5S6/7SvifS). These SIVmac239-derived sequences were expected to protect the virus from HIV-1 restriction factors in monkey cells. However, the replicative capability of NL-4/5S6/7SvifS in human cells was severely impaired. By long-term cultivation of human CEM-SS cells infected with NL-4/5S6/7SvifS, we succeeded in partially rescuing the impaired replicative capability of the virus in human cells. This adapted virus encoded a G-to-E substitution at the 116th position of the CA (NL-4/5SG116E6/7SvifS). In the work described here, we explored the mechanism by which the replicative capability of NL-4/5S6/7SvifS was impaired in human cells. Quantitative analysis (by real-time PCR) of viral DNA synthesis from infected cells revealed that NL-4/5S6/7SvifS had a major defect in nuclear entry. Mutations in CA are known to affect viral core stability and result in deleterious effects in HIV-1 infection; therefore, we measured the kinetics of uncoating of these viruses. The uncoating of NL-4/5S6/7SvifS was significantly slower than that of wild type HIV-1 (WT), whereas the uncoating of NL-4/5SG116E6/7SvifS was similar to that of WT. Our results suggested that the lower replicative capability of NL-4/5S6/7SvifS in human cells was, at least in part, due to the slower uncoating of this virus.
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Affiliation(s)
- Ken Kono
- Department of Viral Infections, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Eri Takeda
- Department of Viral Infections, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Hiromi Tsutsui
- Department of Viral Infections, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Ayumu Kuroishi
- Department of Viral Infections, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Amy E. Hulme
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
| | - Thomas J. Hope
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
| | - Emi E. Nakayama
- Department of Viral Infections, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Tatsuo Shioda
- Department of Viral Infections, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
- * E-mail:
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21
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Yufenyuy EL, Aiken C. The NTD-CTD intersubunit interface plays a critical role in assembly and stabilization of the HIV-1 capsid. Retrovirology 2013; 10:29. [PMID: 23497318 PMCID: PMC3623829 DOI: 10.1186/1742-4690-10-29] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Accepted: 02/18/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Lentiviruses exhibit a cone-shaped capsid composed of subunits of the viral CA protein. The intrinsic stability of the capsid is critical for HIV-1 infection, since both stabilizing and destabilizing mutations compromise viral infectivity. Structural studies have identified three intersubunit interfaces in the HIV-1 capsid, two of which have been previously studied by mutational analysis. In this present study we analyzed the role of a third interface, that which is formed between the amino terminal domain (NTD) and carboxyl terminal domain (CTD) of adjacent subunits. RESULTS We provided evidence for the presence of the NTD-CTD interface in HIV-1 particles by engineering intersubunit NTD-CTD disulfide crosslinks, resulting in accumulation of disulfide-linked oligomers up to hexamers. We also generated and characterized a panel of HIV-1 mutants containing substitutions at this interface. Some mutants showed processing defects and altered morphology from that of wild type, indicating that the interface is important for capsid assembly. Analysis of these mutants by transmission electron microscopy corroborated the importance of this interface in assembly. Other mutants exhibited quantitative changes in capsid stability, many with unstable capsids, and one mutant with a hyperstable capsid. Analysis of the mutants for their capacity to saturate TRIMCyp-mediated restriction in trans confirmed that the unstable mutants undergo premature uncoating in target cells. All but one of the mutants were markedly attenuated in replication owing to impaired reverse transcription in target cells. CONCLUSIONS Our results demonstrate that the NTD-CTD intersubunit interface is present in the mature HIV-1 capsid and is critical for proper capsid assembly and stability.
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Affiliation(s)
- Ernest L Yufenyuy
- Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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22
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Lyonnais S, Gorelick RJ, Heniche-Boukhalfa F, Bouaziz S, Parissi V, Mouscadet JF, Restle T, Gatell JM, Le Cam E, Mirambeau G. A protein ballet around the viral genome orchestrated by HIV-1 reverse transcriptase leads to an architectural switch: from nucleocapsid-condensed RNA to Vpr-bridged DNA. Virus Res 2013; 171:287-303. [PMID: 23017337 PMCID: PMC3552025 DOI: 10.1016/j.virusres.2012.09.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2012] [Revised: 09/13/2012] [Accepted: 09/14/2012] [Indexed: 12/15/2022]
Abstract
HIV-1 reverse transcription is achieved in the newly infected cell before viral DNA (vDNA) nuclear import. Reverse transcriptase (RT) has previously been shown to function as a molecular motor, dismantling the nucleocapsid complex that binds the viral genome as soon as plus-strand DNA synthesis initiates. We first propose a detailed model of this dismantling in close relationship with the sequential conversion from RNA to double-stranded (ds) DNA, focusing on the nucleocapsid protein (NCp7). The HIV-1 DNA-containing pre-integration complex (PIC) resulting from completion of reverse transcription is translocated through the nuclear pore. The PIC nucleoprotein architecture is poorly understood but contains at least two HIV-1 proteins initially from the virion core, namely integrase (IN) and the viral protein r (Vpr). We next present a set of electron micrographs supporting that Vpr behaves as a DNA architectural protein, initiating multiple DNA bridges over more than 500 base pairs (bp). These complexes are shown to interact with NCp7 bound to single-stranded nucleic acid regions that are thought to maintain IN binding during dsDNA synthesis, concurrently with nucleocapsid complex dismantling. This unexpected binding of Vpr conveniently leads to a compacted but filamentous folding of the vDNA that should favor its nuclear import. Finally, nucleocapsid-like aggregates engaged in dsDNA synthesis appear to efficiently bind to F-actin filaments, a property that may be involved in targeting complexes to the nuclear envelope. More generally, this article highlights unique possibilities offered by in vitro reconstitution approaches combined with macromolecular imaging to gain insights into the mechanisms that alter the nucleoprotein architecture of the HIV-1 genome, ultimately enabling its insertion into the nuclear chromatin.
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MESH Headings
- DNA Packaging
- DNA, Viral/chemistry
- DNA, Viral/genetics
- DNA, Viral/metabolism
- Genome, Viral
- HIV Integrase/genetics
- HIV Integrase/metabolism
- HIV Reverse Transcriptase/genetics
- HIV Reverse Transcriptase/metabolism
- HIV-1/chemistry
- HIV-1/enzymology
- HIV-1/genetics
- HIV-1/metabolism
- Humans
- RNA, Viral/chemistry
- RNA, Viral/genetics
- RNA, Viral/metabolism
- Reverse Transcription
- gag Gene Products, Human Immunodeficiency Virus/genetics
- gag Gene Products, Human Immunodeficiency Virus/metabolism
- vpr Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
| | - Robert J. Gorelick
- AIDS and Cancer Virus Program; SAIC-Frederick, Inc.; Frederick National Laboratory for Cancer Research; Frederick, MD USA
| | - Fatima Heniche-Boukhalfa
- Maintenance des génomes, Microscopies Moléculaire et Bionanosciences; UMR 8126 CNRS-Université Paris Sud, Villejuif, F-94805, France
| | - Serge Bouaziz
- Laboratoire de Cristallographie et RMN biologiques; UMR 8015 CNRS-Université Paris Descartes; Paris, F-75006, France
| | - Vincent Parissi
- Laboratoire de Microbiologie Fondamentale et Pathogénicité, UMR5234 CNRS-Université Bordeaux Segalen, France
| | | | - Tobias Restle
- Institute of Molecular Medicine, University of Lübeck, Center for Structural and Cell Biology in Medicine (CSCM), D-23538 Lübeck, Germany
| | | | - Eric Le Cam
- Maintenance des génomes, Microscopies Moléculaire et Bionanosciences; UMR 8126 CNRS-Université Paris Sud, Villejuif, F-94805, France
| | - Gilles Mirambeau
- AIDS Research Group; IDIBAPS; E-08036 Barcelona, Spain
- Faculté de Biologie; UPMC Sorbonne Universités; Paris, F-75005, France
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23
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Jiang J, Ablan S, Derebail S, Hercík K, Soheilian F, Thomas JA, Tang S, Hewlett I, Nagashima K, Gorelick RJ, Freed EO, Levin JG. The interdomain linker region of HIV-1 capsid protein is a critical determinant of proper core assembly and stability. Virology 2011; 421:253-65. [PMID: 22036671 PMCID: PMC3573886 DOI: 10.1016/j.virol.2011.09.012] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Revised: 08/17/2011] [Accepted: 09/14/2011] [Indexed: 11/20/2022]
Abstract
The HIV-1 capsid protein consists of two independently folded domains connected by a flexible peptide linker (residues 146-150), the function of which remains to be defined. To investigate the role of this region in virus replication, we made alanine or leucine substitutions in each linker residue and two flanking residues. Three classes of mutants were identified: (i) S146A and T148A behave like wild type (WT); (ii) Y145A, I150A, and L151A are noninfectious, assemble unstable cores with aberrant morphology, and synthesize almost no viral DNA; and (iii) P147L and S149A display a poorly infectious, attenuated phenotype. Infectivity of P147L and S149A is rescued specifically by pseudotyping with vesicular stomatitis virus envelope glycoprotein. Moreover, despite having unstable cores, these mutants assemble WT-like structures and synthesize viral DNA, although less efficiently than WT. Collectively, these findings demonstrate that the linker region is essential for proper assembly and stability of cores and efficient replication.
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Affiliation(s)
- Jiyang Jiang
- Section on Viral Gene Regulation, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health, National Institutes of Health, Building 6B, Room 216, 6 Center Drive, Bethesda, MD 20892-2780, USA
| | - Sherimay Ablan
- Virus-Cell Interaction Section, Drug Resistance Program, National Cancer Institute Frederick, Frederick, MD 21702-1201, USA
| | - Suchitra Derebail
- Section on Viral Gene Regulation, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health, National Institutes of Health, Building 6B, Room 216, 6 Center Drive, Bethesda, MD 20892-2780, USA
| | - Kamil Hercík
- Section on Viral Gene Regulation, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health, National Institutes of Health, Building 6B, Room 216, 6 Center Drive, Bethesda, MD 20892-2780, USA
| | - Ferri Soheilian
- Image Analysis Laboratory, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, MD 21702-1201, USA
| | - James A. Thomas
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, MD 21702-1201, USA
| | - Shixing Tang
- Laboratory of Molecular Virology, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, MD 20892, USA
| | - Indira Hewlett
- Laboratory of Molecular Virology, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, MD 20892, USA
| | - Kunio Nagashima
- Image Analysis Laboratory, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, MD 21702-1201, USA
| | - Robert J. Gorelick
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, MD 21702-1201, USA
| | - Eric O. Freed
- Virus-Cell Interaction Section, Drug Resistance Program, National Cancer Institute Frederick, Frederick, MD 21702-1201, USA
| | - Judith G. Levin
- Section on Viral Gene Regulation, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health, National Institutes of Health, Building 6B, Room 216, 6 Center Drive, Bethesda, MD 20892-2780, USA
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24
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Abstract
The genome of the retroviruses is encased in a capsid surrounded by a lipid envelope. For lentiviruses, such as HIV-1, the conical capsid shell is composed of CA protein arranged as a lattice of hexagon. The capsid is closed by 7 pentamers at the broad end and 5 at the narrow end of the cone(1, 2). Encased in this capsid shell is the viral ribonucleoprotein complex, and together they comprise the core. Following fusion of the viral membrane with the target cell membrane, the HIV-1 is released into the cytoplasm. The capsid then disassembles releasing free CA in the soluble form(3) in a process referred to as uncoating. The intracellular location and timing of HIV-1 uncoating are poorly understood. Single amino-acid substitutions in CA that alter the stability of the capsid also impair the ability of HIV-1 to infect cells(4). This indicates that the stability of the capsid is critical for HIV-1 infection. HIV-1 uncoating has been difficult to study due to lack of availability of sensitive and reliable assays for this process. Here we describe a quantitative method for studying uncoating in vitro using cores isolated from infectious HIV-1 particles. The approach involves isolation of cores by sedimentation of concentrated virions through a layer of detergent and into a linear sucrose gradient, in the cold. To quantify uncoating, the isolated cores are incubated at 37°C for various timed intervals and subsequently pelleted by ultracentrifugation. The extent of uncoating is analyzed by quantifying the fraction of CA in the supernatant. This approach has been employed to analyze effects of viral mutations on HIV-1 capsid stability(4, 5, 6). It should also be useful for studying the role of cellular factors in HIV-1 uncoating.
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Affiliation(s)
- Vaibhav B Shah
- Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine.
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25
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The inside out of lentiviral vectors. Viruses 2011; 3:132-159. [PMID: 22049307 PMCID: PMC3206600 DOI: 10.3390/v3020132] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2010] [Revised: 01/25/2011] [Accepted: 02/08/2011] [Indexed: 11/30/2022] Open
Abstract
Lentiviruses induce a wide variety of pathologies in different animal species. A common feature of the replicative cycle of these viruses is their ability to target non-dividing cells, a property that constitutes an extremely attractive asset in gene therapy. In this review, we shall describe the main basic aspects of the virology of lentiviruses that were exploited to obtain efficient gene transfer vectors. In addition, we shall discuss some of the hurdles that oppose the efficient genetic modification mediated by lentiviral vectors and the strategies that are being developed to circumvent them.
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26
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Abstract
HIV uncoating is defined as the loss of viral capsid that occurs within the cytoplasm of infected cells before entry of the viral genome into the nucleus. It is an obligatory step of HIV-1 early infection and accompanies the transition between reverse transcription complexes (RTCs), in which reverse transcription occurs, and pre-integration complexes (PICs), which are competent to integrate into the host genome. The study of the nature and timing of HIV-1 uncoating has been paved with difficulties, particularly as a result of the vulnerability of the capsid assembly to experimental manipulation. Nevertheless, recent studies of capsid structure, retroviral restriction and mechanisms of nuclear import, as well as the recent expansion of technical advances in genome-wide studies and cell imagery approaches, have substantially changed our understanding of HIV uncoating. Although early work suggested that uncoating occurs immediately following viral entry in the cell, thus attributing a trivial role for the capsid in infected cells, recent data suggest that uncoating occurs several hours later and that capsid has an all-important role in the cell that it infects: for transport towards the nucleus, reverse transcription and nuclear import. Knowing that uncoating occurs at a later stage suggests that the viral capsid interacts extensively with the cytoskeleton and other cytoplasmic components during its transport to the nucleus, which leads to a considerable reassessment of our efforts to identify potential therapeutic targets for HIV therapy. This review discusses our current understanding of HIV uncoating, the functional interplay between infectivity and timely uncoating, as well as exposing the appropriate methods to study uncoating and addressing the many questions that remain unanswered.
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27
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28
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Briones MS, Dobard CW, Chow SA. Role of human immunodeficiency virus type 1 integrase in uncoating of the viral core. J Virol 2010; 84:5181-90. [PMID: 20219923 PMCID: PMC2863833 DOI: 10.1128/jvi.02382-09] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
After membrane fusion with a target cell, the core of human immunodeficiency virus type 1 (HIV-1) enters into the cytoplasm, where uncoating occurs. The cone-shaped core is composed of the viral capsid protein (CA), which disassembles during uncoating. The underlying factors and mechanisms governing uncoating are poorly understood. Several CA mutations can cause changes in core stability and a block at reverse transcription, demonstrating the requirement for optimal core stability during viral replication. HIV-1 integrase (IN) catalyzes the insertion of the viral cDNA into the host genome, and certain IN mutations are pleiotropic. Similar to some CA mutants, two IN mutants, one with a complete deletion of IN (NL-DeltaIN) and the other with a Cys-to-Ser substitution (NL-C130S), were noninfectious, with a replication block at reverse transcription. Compared to the wild type (WT), the cytoplasmic CA levels of the IN mutants in infected cells were reduced, suggesting accelerated uncoating. The role of IN during uncoating was examined by isolating and characterizing cores from NL-DeltaIN and NL-C130S. Both IN mutants could form functional cores, but the core yield and stability were decreased. Also, virion incorporation of cyclophilin A (CypA), a cellular peptidyl-prolyl isomerase that binds specifically to CA, was decreased in the IN mutants. Cores isolated from WT virus depleted of CypA had an unstable-core phenotype, confirming a role of CypA in promoting optimal core stability. Taken together, our results indicate that IN is required during uncoating for maintaining CypA-CA interaction, which promotes optimal stability of the viral core.
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Affiliation(s)
- Marisa S. Briones
- Department of Molecular and Medical Pharmacology, Molecular Biology Institute and UCLA AIDS Institute, UCLA School of Medicine, Los Angeles, California 90095
| | - Charles W. Dobard
- Department of Molecular and Medical Pharmacology, Molecular Biology Institute and UCLA AIDS Institute, UCLA School of Medicine, Los Angeles, California 90095
| | - Samson A. Chow
- Department of Molecular and Medical Pharmacology, Molecular Biology Institute and UCLA AIDS Institute, UCLA School of Medicine, Los Angeles, California 90095
- Corresponding author. Mailing address: Molecular and Medical Pharmacology, 650 Charles E. Young Dr., CHS 23-133, Los Angeles, CA 90095. Phone: (310) 825-9600. Fax: (310) 825-6267. E-mail:
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29
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Abstract
HIV-1 possesses an exquisite ability to infect cells independently from their cycling status by undergoing an active phase of nuclear import through the nuclear pore. This property has been ascribed to the presence of karyophilic elements present in viral nucleoprotein complexes, such as the matrix protein (MA); Vpr; the integrase (IN); and a cis-acting structure present in the newly synthesized DNA, the DNA flap. However, their role in nuclear import remains controversial at best. In the present study, we carried out a comprehensive analysis of the role of these elements in nuclear import in a comparison between several primary cell types, including stimulated lymphocytes, macrophages, and dendritic cells. We show that despite the fact that none of these elements is absolutely required for nuclear import, disruption of the central polypurine tract-central termination sequence (cPPT-CTS) clearly affects the kinetics of viral DNA entry into the nucleus. This effect is independent of the cell cycle status of the target cells and is observed in cycling as well as in nondividing primary cells, suggesting that nuclear import of viral DNA may occur similarly under both conditions. Nonetheless, this study indicates that other components are utilized along with the cPPT-CTS for an efficient entry of viral DNA into the nucleus.
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30
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Abstract
Uncoating is an essential step in the retrovirus life cycle about which little is known. Uncoating is defined as the specific dissociation of the capsid shell from the viral core in the host cell cytoplasm. In this chapter, biochemical assays for studying HIV-1 uncoating in vitro are described. These techniques have proven useful for characterizing HIV-1 mutants that exhibit defects in the uncoating step of infection.
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31
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Brun S, Solignat M, Gay B, Bernard E, Chaloin L, Fenard D, Devaux C, Chazal N, Briant L. VSV-G pseudotyping rescues HIV-1 CA mutations that impair core assembly or stability. Retrovirology 2008; 5:57. [PMID: 18605989 PMCID: PMC2474847 DOI: 10.1186/1742-4690-5-57] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2008] [Accepted: 07/07/2008] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND The machinery of early HIV-1 replication still remains to be elucidated. Recently the viral core was reported to persist in the infected cell cytoplasm as an assembled particle, giving rise to the reverse transcription complex responsible for the synthesis of proviral DNA and its transport to the nucleus. Numerous studies have demonstrated that reverse transcription of the HIV-1 genome into proviral DNA is tightly dependent upon proper assembly of the capsid (CA) protein into mature cores that display appropriate stability. The functional impact of structural properties of the core in early replicative steps has yet to be determined. RESULTS Here, we show that infectivity of HIV-1 mutants bearing S149A and S178A mutations in CA can be efficiently restored when pseudotyped with vesicular stomatitis virus envelope glycoprotein, that addresses the mutant cores through the endocytic pathway rather than by fusion at the plasma membrane. The mechanisms by which these mutations disrupt virus infectivity were investigated. S149A and S178A mutants were unable to complete reverse transcription and/or produce 2-LTR DNA. Morphological analysis of viral particles and in vitro uncoating assays of isolated cores demonstrated that infectivity defects resulted from disruption of the viral core assembly and stability for S149A and S178A mutants, respectively. Consistent with these results, both mutants failed to saturate TRIM-antiviral restriction activity. CONCLUSION Defects generated at the level of core assembly and stability by S149A and S178A mutations are sensitive to the way of delivery of viral nucleoprotein complexes into the target cell. Addressing CA mutants through the endocytic pathway may compensate for defects generated at the reverse transcription/nuclear import level subsequent to impairment of core assembly or stability.
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Affiliation(s)
- Sonia Brun
- Université Montpellier 1, Centre d'études d'agents Pathogènes et Biotechnologies pour Santé, France.
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32
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Nucleocapsid protein function in early infection processes. Virus Res 2008; 134:39-63. [PMID: 18279991 DOI: 10.1016/j.virusres.2007.12.006] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Revised: 12/13/2007] [Accepted: 12/13/2007] [Indexed: 01/15/2023]
Abstract
The role of nucleocapsid protein (NC) in the early steps of retroviral replication appears largely that of a facilitator for reverse transcription and integration. Using a wide variety of cell-free assay systems, the properties of mature NC proteins (e.g. HIV-1 p7(NC) or MLV p10(NC)) as nucleic acid chaperones have been extensively investigated. The effect of NC on tRNA annealing, reverse transcription initiation, minus-strand-transfer, processivity of reverse transcription, plus-strand-transfer, strand-displacement synthesis, 3' processing of viral DNA by integrase, and integrase-mediated strand-transfer has been determined by a large number of laboratories. Interestingly, these reactions can all be accomplished to varying degrees in the absence of NC; some are facilitated by both viral and non-viral proteins and peptides that may or may not be involved in vivo. What is one to conclude from the observation that NC is not strictly required for these necessary reactions to occur? NC likely enhances the efficiency of each of these steps, thereby vastly improving the productivity of infection. In other words, one of the major roles of NC is to enhance the effectiveness of early infection, thereby increasing the probability of productive replication and ultimately of retrovirus survival.
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