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Hogan V, Johnson WE. Unique Structure and Distinctive Properties of the Ancient and Ubiquitous Gamma-Type Envelope Glycoprotein. Viruses 2023; 15:v15020274. [PMID: 36851488 PMCID: PMC9967133 DOI: 10.3390/v15020274] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 01/13/2023] [Accepted: 01/15/2023] [Indexed: 01/20/2023] Open
Abstract
After the onset of the AIDS pandemic, HIV-1 (genus Lentivirus) became the predominant model for studying retrovirus Env glycoproteins and their role in entry. However, HIV Env is an inadequate model for understanding entry of viruses in the Alpharetrovirus, Gammaretrovirus and Deltaretrovirus genera. For example, oncogenic model system viruses such as Rous sarcoma virus (RSV, Alpharetrovirus), murine leukemia virus (MLV, Gammaretrovirus) and human T-cell leukemia viruses (HTLV-I and HTLV-II, Deltaretrovirus) encode Envs that are structurally and functionally distinct from HIV Env. We refer to these as Gamma-type Envs. Gamma-type Envs are probably the most widespread retroviral Envs in nature. They are found in exogenous and endogenous retroviruses representing a broad spectrum of vertebrate hosts including amphibians, birds, reptiles, mammals and fish. In endogenous form, gamma-type Envs have been evolutionarily coopted numerous times, most notably as placental syncytins (e.g., human SYNC1 and SYNC2). Remarkably, gamma-type Envs are also found outside of the Retroviridae. Gp2 proteins of filoviruses (e.g., Ebolavirus) and snake arenaviruses in the genus Reptarenavirus are gamma-type Env homologs, products of ancient recombination events involving viruses of different Baltimore classes. Distinctive hallmarks of gamma-type Envs include a labile disulfide bond linking the surface and transmembrane subunits, a multi-stage attachment and fusion mechanism, a highly conserved (but poorly understood) "immunosuppressive domain", and activation by the viral protease during virion maturation. Here, we synthesize work from diverse retrovirus model systems to illustrate these distinctive properties and to highlight avenues for further exploration of gamma-type Env structure and function.
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DNA origami signposts for identifying proteins on cell membranes by electron cryotomography. Cell 2021; 184:1110-1121.e16. [PMID: 33606980 PMCID: PMC7895908 DOI: 10.1016/j.cell.2021.01.033] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Revised: 09/14/2020] [Accepted: 01/20/2021] [Indexed: 12/21/2022]
Abstract
Electron cryotomography (cryoET), an electron cryomicroscopy (cryoEM) modality, has changed our understanding of biological function by revealing the native molecular details of membranes, viruses, and cells. However, identification of individual molecules within tomograms from cryoET is challenging because of sample crowding and low signal-to-noise ratios. Here, we present a tagging strategy for cryoET that precisely identifies individual protein complexes in tomograms without relying on metal clusters. Our method makes use of DNA origami to produce “molecular signposts” that target molecules of interest, here via fluorescent fusion proteins, providing a platform generally applicable to biological surfaces. We demonstrate the specificity of signpost origami tags (SPOTs) in vitro as well as their suitability for cryoET of membrane vesicles, enveloped viruses, and the exterior of intact mammalian cells. Asymmetric DNA signpost origami tags (SPOTs) precisely localize proteins SPOTs identify specific proteins in electron cryomicroscopy SPOTs have a high contrast “sign” and functionalized “post” base for targeting SPOTs recognize fluorescent fusion proteins on vesicles, viruses, and cell surfaces
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Izaguirre G. The Proteolytic Regulation of Virus Cell Entry by Furin and Other Proprotein Convertases. Viruses 2019; 11:v11090837. [PMID: 31505793 PMCID: PMC6784293 DOI: 10.3390/v11090837] [Citation(s) in RCA: 101] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Revised: 09/03/2019] [Accepted: 09/06/2019] [Indexed: 12/11/2022] Open
Abstract
A wide variety of viruses exploit furin and other proprotein convertases (PCs) of the constitutive protein secretion pathway in order to regulate their cell entry mechanism and infectivity. Surface proteins of enveloped, as well as non-enveloped, viruses become processed by these proteases intracellularly during morphogenesis or extracellularly after egress and during entry in order to produce mature virions activated for infection. Although viruses also take advantage of other proteases, it is when some viruses become reactive with PCs that they may develop high pathogenicity. Besides reacting with furin, some viruses may also react with the PCs of the other specificity group constituted by PC4/PC5/PACE4/PC7. The targeting of PCs for inhibition may result in a useful strategy to treat infections with some highly pathogenic viruses. A wide variety of PC inhibitors have been developed and tested for their antiviral activity in cell-based assays.
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Affiliation(s)
- Gonzalo Izaguirre
- College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612, USA.
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Braun E, Hotter D, Koepke L, Zech F, Groß R, Sparrer KM, Müller JA, Pfaller CK, Heusinger E, Wombacher R, Sutter K, Dittmer U, Winkler M, Simmons G, Jakobsen MR, Conzelmann KK, Pöhlmann S, Münch J, Fackler OT, Kirchhoff F, Sauter D. Guanylate-Binding Proteins 2 and 5 Exert Broad Antiviral Activity by Inhibiting Furin-Mediated Processing of Viral Envelope Proteins. Cell Rep 2019; 27:2092-2104.e10. [DOI: 10.1016/j.celrep.2019.04.063] [Citation(s) in RCA: 73] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Revised: 03/11/2019] [Accepted: 04/12/2019] [Indexed: 12/13/2022] Open
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Omotuyi OI, Hamada T. Human furin Cys198 imposes dihedral and positional restraints on His194 for optimal Ser386-proton transfer. J Biomol Struct Dyn 2015; 33:2442-51. [DOI: 10.1080/07391102.2015.1041552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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6
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Zhang W, Cao S, Martin JL, Mueller JD, Mansky LM. Morphology and ultrastructure of retrovirus particles. AIMS BIOPHYSICS 2015; 2:343-369. [PMID: 26448965 PMCID: PMC4593330 DOI: 10.3934/biophy.2015.3.343] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Retrovirus morphogenesis entails assembly of Gag proteins and the viral genome on the host plasma membrane, acquisition of the viral membrane and envelope proteins through budding, and formation of the core through the maturation process. Although in both immature and mature retroviruses, Gag and capsid proteins are organized as paracrystalline structures, the curvatures of these protein arrays are evidently not uniform within one or among all virus particles. The heterogeneity of retroviruses poses significant challenges to studying the protein contacts within the Gag and capsid lattices. This review focuses on current understanding of the molecular organization of retroviruses derived from the sub-nanometer structures of immature virus particles, helical capsid protein assemblies and soluble envelope protein complexes. These studies provide insight into the molecular elements that maintain the stability, flexibility and infectivity of virus particles. Also reviewed are morphological studies of retrovirus budding, maturation, infection and cell-cell transmission, which inform the structural transformation of the viruses and the cells during infection and viral transmission, and lead to better understanding of the interplay between the functioning viral proteins and the host cell.
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Affiliation(s)
- Wei Zhang
- Institute for Molecular Virology, University of Minnesota, Minneapolis, MN, USA ; Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, USA ; Characterization Facility, University of Minnesota, Minneapolis, MN, USA
| | - Sheng Cao
- Wuhan Institute of Virology, Chinese Academy of Science, Wuhan, China
| | - Jessica L Martin
- Institute for Molecular Virology, University of Minnesota, Minneapolis, MN, USA ; Pharmacology Graduate Program, University of Minnesota, Minneapolis, MN, USA
| | - Joachim D Mueller
- Institute for Molecular Virology, University of Minnesota, Minneapolis, MN, USA ; School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA
| | - Louis M Mansky
- Institute for Molecular Virology, University of Minnesota, Minneapolis, MN, USA ; Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, USA ; Pharmacology Graduate Program, University of Minnesota, Minneapolis, MN, USA ; Department of Microbiology, University of Minnesota, Minneapolis, MN, USA
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Moscoso CG, Xing L, Hui J, Hu J, Kalkhoran MB, Yenigun OM, Sun Y, Paavolainen L, Martin L, Vahlne A, Zambonelli C, Barnett SW, Srivastava IK, Cheng RH. Trimeric HIV Env provides epitope occlusion mediated by hypervariable loops. Sci Rep 2014; 4:7025. [PMID: 25395053 PMCID: PMC4231788 DOI: 10.1038/srep07025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Accepted: 08/26/2014] [Indexed: 12/17/2022] Open
Abstract
Hypervariable loops of HIV-1 Env protein gp120 are speculated to play roles in the conformational transition of Env to the receptor binding-induced metastable state. Structural analysis of full-length Env-based immunogens, containing the entire V2 loop, displayed tighter association between gp120 subunits, resulting in a smaller trimeric diameter than constructs lacking V2. A prominent basal quaternary location of V2 and V3′ that challenges previous reports would facilitate gp41-independent gp120-gp120 interactions and suggests a quaternary mechanism of epitope occlusion facilitated by hypervariable loops. Deletion of V2 resulted in dramatic exposure of basal, membrane-proximal gp41 epitopes, consistent with its predicted basal location. The structural features of HIV-1 Env characterized here provide grounds for a paradigm shift in loop exposure and epitope occlusion, while providing substantive rationale for epitope display required for elicitation of broadly neutralizing antibodies, as well as substantiating previous pertinent literature disregarded in recent reports.
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Affiliation(s)
- Carlos G Moscoso
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Li Xing
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Jinwen Hui
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Jeffrey Hu
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | | | - Onur M Yenigun
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Yide Sun
- Novartis Vaccines and Diagnostics Inc., 45 Sydney Street, Cambridge, MA 02139
| | - Lassi Paavolainen
- Department of Biological and Environmental Science/Nanoscience Center, University of Jyväskylä, FI-40351 Jyväskylä, Finland
| | - Loïc Martin
- Commissariat à l'énergie atomique et aux énergies alternatives, Institut de Biologie et Technologies de Saclay, Service d'Ingénierie Moléculaire des Protéines, Gif-sur-Yvette F-91191, France
| | - Anders Vahlne
- Karolinska Institutet, Structural Virology, Clinical Microbiology/University Hospital, 171 77 Stockholm, Sweden
| | - Carlo Zambonelli
- Novartis Vaccines and Diagnostics Inc., 45 Sydney Street, Cambridge, MA 02139
| | - Susan W Barnett
- Novartis Vaccines and Diagnostics Inc., 45 Sydney Street, Cambridge, MA 02139
| | | | - R Holland Cheng
- 1] Department of Molecular and Cellular Biology, University of California, Davis, CA 95616 [2] Karolinska Institutet, Structural Virology, Clinical Microbiology/University Hospital, 171 77 Stockholm, Sweden
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