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González SA, Affranchino JL. The impact of mutations affecting highly conserved amino acids in the simian immunodeficiency virus nucleocapsid protein on virion assembly, genomic RNA packaging and viral infectivity. Virology 2023; 578:163-170. [PMID: 36580863 DOI: 10.1016/j.virol.2022.12.007] [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: 11/15/2022] [Revised: 12/12/2022] [Accepted: 12/15/2022] [Indexed: 12/24/2022]
Abstract
The nucleocapsid (NC) domain of the retroviral Gag polyproteins mediates the incorporation of the viral genomic RNA into virions. Although SIV is widely used as a model for human immunodeficiency virus type 1 (HIV-1) infections, the SIV NC has been the subject of few studies which have provided discrepant data on the relative contribution of the two NC zinc finger motifs to genomic RNA encapsidation. Here, we demonstrate that mutations affecting the first cysteine in the distal zinc finger motif (C33S) or the N-terminal NC basic domain (R7A/K8A) drastically impair virion assembly and viral RNA binding. By contrast, amino acid substitutions targeting the first cysteine of the proximal zinc finger (C12S) or the basic region connecting both zinc fingers (R29A/R30A) allow substantial particle production and genomic RNA encapsidation. Our results help define the relative contribution of the SIV NC zinc finger motifs and basic regions to the NC biological properties.
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Affiliation(s)
- Silvia A González
- Laboratorio de Virología, Facultad de Ciencias Exactas y Naturales, Universidad de Belgrano (UB), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.
| | - José L Affranchino
- Centro de Virología Humana y Animal (CEVHAN), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Abierta Interamericana (UAI), Buenos Aires, Argentina
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2
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Mangala Prasad V, Leaman DP, Lovendahl KN, Croft JT, Benhaim MA, Hodge EA, Zwick MB, Lee KK. Cryo-ET of Env on intact HIV virions reveals structural variation and positioning on the Gag lattice. Cell 2022; 185:641-653.e17. [PMID: 35123651 PMCID: PMC9000915 DOI: 10.1016/j.cell.2022.01.013] [Citation(s) in RCA: 36] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Revised: 10/19/2021] [Accepted: 01/18/2022] [Indexed: 01/11/2023]
Abstract
HIV-1 Env mediates viral entry into host cells and is the sole target for neutralizing antibodies. However, Env structure and organization in its native virion context has eluded detailed characterization. Here, we used cryo-electron tomography to analyze Env in mature and immature HIV-1 particles. Immature particles showed distinct Env positioning relative to the underlying Gag lattice, providing insights into long-standing questions about Env incorporation. A 9.1-Å sub-tomogram-averaged reconstruction of virion-bound Env in conjunction with structural mass spectrometry revealed unexpected features, including a variable central core of the gp41 subunit, heterogeneous glycosylation between protomers, and a flexible stalk that allows Env tilting and variable exposure of neutralizing epitopes. Together, our results provide an integrative understanding of HIV assembly and structural variation in Env antigen presentation.
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Affiliation(s)
- Vidya Mangala Prasad
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Daniel P Leaman
- Department of Immunology and Microbiology, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Klaus N Lovendahl
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Jacob T Croft
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Mark A Benhaim
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Edgar A Hodge
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Michael B Zwick
- Department of Immunology and Microbiology, The Scripps Research Institute, La Jolla, CA 92037, USA.
| | - Kelly K Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA; Biological Physics, Structure and Design Graduate Program, University of Washington, Seattle, WA 98195, USA; Department of Microbiology, University of Washington, Seattle, WA 98195, USA.
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3
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Giraudy I, Ovejero CA, Affranchino JL, González SA. In vitro inhibitory effect of maraviroc on the association of the simian immunodeficiency virus envelope glycoprotein with CCR5. Virus Genes 2021; 57:106-110. [PMID: 33400102 DOI: 10.1007/s11262-020-01816-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 11/29/2020] [Indexed: 11/29/2022]
Abstract
Asian macaques infected with simian immunodeficiency viruses (SIVs) isolated from African non-human primates develop a disease similar to human AIDS. SIV enters its target cells by binding to CD4 and a coreceptor, typically CCR5. Maraviroc is an entry inhibitor of human immunodeficiency virus type 1 (HIV-1) that prevents the interaction between CCR5 and the surface subunit gp120 of the viral envelope glycoprotein (Env). Thus far, the activity of maraviroc on SIV entry has been poorly studied. Here, we determined in vitro pharmacological parameters of the effect of maraviroc on the SIV Env association with CCR5. Cell-to-cell fusion inhibition assays were used to compare the susceptibility to maraviroc of the SIVsmmPBj Env-CCR5 interaction with that of HIV-1BaL Env. Analysis of dose-response curves and determination of IC50 values demonstrate that increasing concentrations of maraviroc inhibit the membrane fusion activity of SIVsmmPBj Env in a manner and to an extent similar to that of HIV-1BaL Env.
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Affiliation(s)
- Ignacio Giraudy
- Laboratorio de Virología, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Universidad de Belgrano, Villanueva 1324, C1426BMJ, Buenos Aires, Argentina
| | - César A Ovejero
- Laboratorio de Virología, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Universidad de Belgrano, Villanueva 1324, C1426BMJ, Buenos Aires, Argentina
| | - José L Affranchino
- Laboratorio de Virología, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Universidad de Belgrano, Villanueva 1324, C1426BMJ, Buenos Aires, Argentina
| | - Silvia A González
- Laboratorio de Virología, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Universidad de Belgrano, Villanueva 1324, C1426BMJ, Buenos Aires, Argentina.
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Salimi H, Johnson J, Flores MG, Zhang MS, O'Malley Y, Houtman JC, Schlievert PM, Haim H. The lipid membrane of HIV-1 stabilizes the viral envelope glycoproteins and modulates their sensitivity to antibody neutralization. J Biol Chem 2019; 295:348-362. [PMID: 31757809 DOI: 10.1074/jbc.ra119.009481] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 11/19/2019] [Indexed: 11/06/2022] Open
Abstract
The envelope glycoproteins (Envs) of HIV-1 are embedded in the cholesterol-rich lipid membrane of the virus. Chemical depletion of cholesterol from HIV-1 particles inactivates their infectivity. We observed that diverse HIV-1 strains exhibit a range of sensitivities to such treatment. Differences in sensitivity to cholesterol depletion could not be explained by variation in Env components known to interact with cholesterol, including the cholesterol-recognition motif and cytoplasmic tail of gp41. Using antibody-binding assays, measurements of virus infectivity, and analyses of lipid membrane order, we found that depletion of cholesterol from HIV-1 particles decreases the conformational stability of Env. It enhances exposure of partially cryptic epitopes on the trimer and increases sensitivity to structure-perturbing treatments such as antibodies and cold denaturation. Substitutions in the cholesterol-interacting motif of gp41 induced similar effects as depletion of cholesterol. Surface-acting agents, which are incorporated into the virus lipid membrane, caused similar effects as disruption of the Env-cholesterol interaction. Furthermore, substitutions in gp120 that increased structural stability of Env (i.e. induced a "closed" conformation of the trimer) increased virus resistance to cholesterol depletion and to the surface-acting agents. Collectively, these results indicate a critical contribution of the viral membrane to the stability of the Env trimer and to neutralization resistance against antibodies. Our findings suggest that the potency of poorly neutralizing antibodies, which are commonly elicited in vaccinated individuals, may be markedly enhanced by altering the lipid composition of the viral membrane.
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Affiliation(s)
- Hamid Salimi
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Jacklyn Johnson
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Manuel G Flores
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Michael S Zhang
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Yunxia O'Malley
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Jon C Houtman
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Patrick M Schlievert
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Hillel Haim
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242.
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Walsh SR, de Jong JG, van Vloten JP, Gerpe MCR, Santry LA, Wootton SK. Truncation of the enzootic nasal tumor virus envelope protein cytoplasmic tail increases Env-mediated fusion and infectivity. J Gen Virol 2017; 98:108-120. [PMID: 27902399 DOI: 10.1099/jgv.0.000654] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Enzootic nasal tumor virus (ENTV) and Jaagsiekte sheep retrovirus (JSRV) are highly related ovine betaretroviruses that induce nasal and lung tumours in small ruminants, respectively. While the ENTV and JSRV envelope (Env) glycoproteins mediate virus entry using the same cellular receptor, the glycosylphosphatidylinositol-linked protein hyaluronoglucosaminidase, ENTV Env pseudovirions mediate entry into cells from a much more restricted range of species than do JSRV Env pseudovirions. Unlike JSRV Env, ENTV Env does not induce cell fusion at pH 5.0 or above, but rather requires a much lower pH (4.0-4.5) for fusion to occur. The cytoplasmic tail of retroviral envelope proteins is a key modulator of envelope-mediated fusion and pseudotype efficiency, especially in the context of virions composed of heterologous Gag proteins. Here we report that progressive truncation of the ENTV Env cytoplasmic tail improves transduction efficiency of pseudotyped retroviral vectors and that complete truncation of the ENTV Env cytoplasmic tail increases transduction efficiency to wild-type JSRV Env levels by increasing fusogenicity without affecting sensitivity to inhibition by lysosomotropic agents, subcellular localization or efficiency of inclusion into virions. Truncation of the cytoplasmic domain of ENTV Env resulted in a significant advantage in viral entry into all cell types tested, including foetal ovine lung and nasal cells. Taken together, we demonstrate that the cytoplasmic tail modulates the fusion activity of the ENTV Env protein and that truncation of this region enhances Eenv-mediated entry into target cells.
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Affiliation(s)
- Scott R Walsh
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
| | - Jondavid G de Jong
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
| | - Jacob P van Vloten
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
| | | | - Lisa A Santry
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
| | - Sarah K Wootton
- Present address: McMaster Immunology Research Centre, McMaster University, Hamilton, ON, Canada.,Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
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Processing, fusogenicity, virion incorporation and CXCR4-binding activity of a feline immunodeficiency virus envelope glycoprotein lacking the two conserved N-glycosylation sites at the C-terminus of the V3 domain. Arch Virol 2016; 161:1761-8. [PMID: 27020572 DOI: 10.1007/s00705-016-2843-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 03/21/2016] [Indexed: 01/07/2023]
Abstract
The process of feline immunodeficiency virus (FIV) entry into its target cells is initiated by the association of the surface (SU) subunit of the viral envelope glycoprotein (Env) with the cellular receptors CD134 and CXCR4. This event is followed by the fusion of the viral and cellular membranes, which is mediated by the transmembrane (TM) subunit of Env. We and others have previously demonstrated that the V3 domain of the SU subunit of Env is essential for CXCR4 binding. Of note, there are two contiguous and highly conserved potential N-glycosylation sites ((418)NST(420) and (422)NLT(424)) located at the C-terminal side of the V3 domain. We therefore decided to study the relevance for Env functions of these N-glycosylation motifs and found that disruption of both of them by introducing the N418Q/N422Q double amino acid substitution drastically impairs Env processing into the SU and TM subunits. Moreover, the simultaneous mutation of these N-glycosylation sites prevents Env incorporation into virions and Env-mediated cell-to-cell fusion. Notably, a recombinant soluble version of the SU glycoprotein carrying the double amino acid replacement N418Q/N422Q at the V3 C-terminal side binds to CXCR4 with an efficiency similar to that of wild-type SU.
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7
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Esteva MJ, Affranchino JL, González SA. Lentiviral Gag assembly analyzed through the functional characterization of chimeric simian immunodeficiency viruses expressing different domains of the feline immunodeficiency virus capsid protein. PLoS One 2014; 9:e114299. [PMID: 25462889 PMCID: PMC4252113 DOI: 10.1371/journal.pone.0114299] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Accepted: 11/07/2014] [Indexed: 12/18/2022] Open
Abstract
To gain insight into the functional relationship between the capsid (CA) domains of the Gag polyproteins of simian and feline immunodeficiency viruses (SIV and FIV, respectively), we constructed chimeric SIVs in which the CA-coding region was partially or totally replaced by the equivalent region of the FIV CA. The phenotypic characterization of the chimeras allowed us to group them into three categories: the chimeric viruses that, while being assembly-competent, exhibit a virion-associated unstable FIV CA; a second group represented only by the chimeric SIV carrying the N-terminal domain (NTD) of the FIV CA which proved to be assembly-defective; and a third group constituted by the chimeric viruses that produce virions exhibiting a mature and stable FIV CA protein, and which incorporate the envelope glycoprotein and contain wild-type levels of viral genome RNA and reverse transcriptase. Further analysis of the latter group of chimeric SIVs demonstrated that they are non-infectious due to a post-entry impairment, such as uncoating of the viral core, reverse transcription or nuclear import of the preintegration complex. Furthermore, we show here that the carboxyl-terminus domain (CTD) of the FIV CA has an intrinsic ability to dimerize in vitro and form high-molecular-weight oligomers, which, together with our finding that the FIV CA-CTD is sufficient to confer assembly competence to the resulting chimeric SIV Gag polyprotein, provides evidence that the CA-CTD exhibits more functional plasticity than the CA-NTD. Taken together, our results provide relevant information on the biological relationship between the CA proteins of primate and nonprimate lentiviruses.
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Affiliation(s)
- María J. Esteva
- Laboratorio de Virología, Universidad de Belgrano (UB) and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - José L. Affranchino
- Laboratorio de Virología, Universidad de Belgrano (UB) and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Silvia A. González
- Laboratorio de Virología, Universidad de Belgrano (UB) and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
- * E-mail:
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8
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Affranchino JL, González SA. Understanding the process of envelope glycoprotein incorporation into virions in simian and feline immunodeficiency viruses. Viruses 2014; 6:264-83. [PMID: 24441862 PMCID: PMC3917442 DOI: 10.3390/v6010264] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Revised: 01/01/2014] [Accepted: 01/06/2014] [Indexed: 12/18/2022] Open
Abstract
The lentiviral envelope glycoproteins (Env) mediate virus entry by interacting with specific receptors present at the cell surface, thereby determining viral tropism and pathogenesis. Therefore, Env incorporation into the virions formed by assembly of the viral Gag polyprotein at the plasma membrane of the infected cells is a key step in the replication cycle of lentiviruses. Besides being useful models of human immunodeficiency virus (HIV) infections in humans and valuable tools for developing AIDS therapies and vaccines, simian and feline immunodeficiency viruses (SIV and FIV, respectively) are relevant animal retroviruses; the study of which provides important information on how lentiviral replication strategies have evolved. In this review, we discuss the molecular mechanisms underlying the incorporation of the SIV and FIV Env glycoproteins into viral particles.
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Affiliation(s)
- José L Affranchino
- Laboratorio de Virología, CONICET-Universidad de Belgrano (UB), Buenos Aires C1426BMJ, Argentina.
| | - Silvia A González
- Laboratorio de Virología, CONICET-Universidad de Belgrano (UB), Buenos Aires C1426BMJ, Argentina.
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Bakouche N, Vandenbroucke AT, Goubau P, Ruelle J. Study of the HIV-2 Env cytoplasmic tail variability and its impact on Tat, Rev and Nef. PLoS One 2013; 8:e79129. [PMID: 24223892 PMCID: PMC3815105 DOI: 10.1371/journal.pone.0079129] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Accepted: 09/18/2013] [Indexed: 11/24/2022] Open
Abstract
Background The HIV-2 env’s 3’ end encodes the cytoplasmic tail (CT) of the Env protein. This genomic region also encodes the rev, Tat and Nef protein in overlapping reading frames. We studied the variability in the CT coding region in 46 clinical specimens and in 2 reference strains by sequencing and by culturing. The aims were to analyse the variability of Env CT and the evolution of proteins expressed from overlapping coding sequences. Results A 70% reduction of the length of the CT region affected the HIV-2 ROD and EHO strains invitro due to a premature stop codon in the env gene. In clinical samples this wasn’t observed, but the CT length varied due to insertions and deletions. We noted 3 conserved and 3 variable regions in the CT. The conserved regions were those containing residues involved in Env endocytosis, the potential HIV-2 CT region implicated in the NF-kB activation and the potential end of the lentiviral lytic peptide one. The variable regions were the potential HIV-2 Kennedy region, the potential lentiviral lytic peptide two and the beginning of the potential lentiviral lytic peptide one. A very hydrophobic region was coded downstream of the premature stop codon observed invitro, suggesting a membrane spanning region. Interestingly, the nucleotides that are responsible for the variability of the CT don’t impact rev and Nef. However, in the Kennedy-like coding region variability resulted only from nucleotide changes that impacted Env and Tat together. Conclusion The HIV-2 Env, Tat and Rev C-terminal part are subject to major length variations in both clinical samples and cultured strains. The HIV-2 Env CT contains variable and conserved regions. These regions don’t affect the rev and Nef amino acids composition which evolves independently. In contrast, Tat co-evolves with the Env CT.
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Affiliation(s)
- Nordine Bakouche
- Institut de recherche expérimentale et clinique, Université catholique de Louvain, Brussels, Belgium
| | | | - Patrick Goubau
- Institut de recherche expérimentale et clinique, Université catholique de Louvain, Brussels, Belgium
| | - Jean Ruelle
- Institut de recherche expérimentale et clinique, Université catholique de Louvain, Brussels, Belgium
- * E-mail:
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Santos da Silva E, Mulinge M, Perez Bercoff D. The frantic play of the concealed HIV envelope cytoplasmic tail. Retrovirology 2013; 10:54. [PMID: 23705972 PMCID: PMC3686653 DOI: 10.1186/1742-4690-10-54] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 05/01/2013] [Indexed: 11/18/2022] Open
Abstract
Lentiviruses have unusually long envelope (Env) cytoplasmic tails, longer than those of other retroviruses. Whereas the Env ectodomain has received much attention, the gp41 cytoplasmic tail (gp41-CT) is one of the least studied parts of the virus. It displays relatively high conservation compared to the rest of Env. It has been long established that the gp41-CT interacts with the Gag precursor protein to ensure Env incorporation into the virion. The gp41-CT contains distinct motifs and domains that mediate both intensive Env intracellular trafficking and interactions with numerous cellular and viral proteins, optimizing viral infectivity. Although they are not fully understood, a multiplicity of interactions between the gp41-CT and cellular factors have been described over the last decade; these interactions illustrate how Env expression and incorporation into virions is a finely tuned process that has evolved to best exploit the host system with minimized genetic information. This review addresses the structure and topology of the gp41-CT of lentiviruses (mainly HIV and SIV), their domains and believed functions. It also considers the cellular and viral proteins that have been described to interact with the gp41-CT, with a particular focus on subtype-related polymorphisms.
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González SA, Paladino MG, Affranchino JL. Palmitoylation of the feline immunodeficiency virus envelope glycoprotein and its effect on fusion activity and envelope incorporation into virions. Virology 2012; 428:1-10. [PMID: 22503389 PMCID: PMC7111954 DOI: 10.1016/j.virol.2012.03.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2012] [Revised: 03/10/2012] [Accepted: 03/14/2012] [Indexed: 11/13/2022]
Abstract
The feline immunodeficiency virus (FIV) envelope glycoprotein (Env) possesses a short cytoplasmic domain of 53 amino acids containing four highly conserved cysteines at Env positions 804, 811, 815 and 848. Since palmitoylation of transmembrane proteins occurs at or near the membrane anchor, we investigated whether cysteines 804, 811 and 815 are acylated and analyzed the relevance of these residues for Env functions. Replacement of cysteines 804, 811 and 815 individually or in combination by serine residues resulted in Env glycoproteins that were efficiently expressed and processed. However, mutations C804S and C811S reduced Env fusogenicity by 93% and 84%, respectively, compared with wild-type Env. By contrast, mutant C815S exhibited a fusogenic capacity representing 50% of the wild-type value. Remarkably, the double mutation C804S/C811S abrogated both Env fusion activity and Env incorporation into virions. Finally, by means of Click chemistry assays we demonstrated that the four FIV Env cytoplasmic cysteines are palmitoylated.
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Affiliation(s)
- Silvia A González
- Laboratorio de Virología, CONICET-Universidad de Belgrano (UB), Villanueva 1324 (C1426BMJ), Buenos Aires, Argentina
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Checkley MA, Luttge BG, Freed EO. HIV-1 envelope glycoprotein biosynthesis, trafficking, and incorporation. J Mol Biol 2011; 410:582-608. [PMID: 21762802 PMCID: PMC3139147 DOI: 10.1016/j.jmb.2011.04.042] [Citation(s) in RCA: 322] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2011] [Revised: 04/14/2011] [Accepted: 04/15/2011] [Indexed: 12/13/2022]
Abstract
The HIV-1 envelope (Env) glycoproteins play an essential role in the virus replication cycle by mediating the fusion between viral and cellular membranes during the entry process. The Env glycoproteins are synthesized as a polyprotein precursor (gp160) that is cleaved by cellular proteases to the mature surface glycoprotein gp120 and the transmembrane glycoprotein gp41. During virus assembly, the gp120/gp41 complex is incorporated as heterotrimeric spikes into the lipid bilayer of nascent virions. These gp120/gp41 complexes then initiate the infection process by binding receptor and coreceptor on the surface of target cells. Much is currently known about the HIV-1 Env glycoprotein trafficking pathway and the structure of gp120 and the extracellular domain of gp41. However, the mechanism by which the Env glycoprotein complex is incorporated into virus particles remains incompletely understood. Genetic data support a major role for the cytoplasmic tail of gp41 and the matrix domain of Gag in Env glycoprotein incorporation. Still to be defined are the identities of host cell factors that may promote Env incorporation and the role of specific membrane microdomains in this process. Here, we review our current understanding of HIV-1 Env glycoprotein trafficking and incorporation into virions.
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Affiliation(s)
- Mary Ann Checkley
- Virus-Cell Interaction Section, HIV Drug Resistance Program National Cancer Institute Frederick, MD 21702
| | - Benjamin G. Luttge
- Virus-Cell Interaction Section, HIV Drug Resistance Program National Cancer Institute Frederick, MD 21702
| | - Eric O. Freed
- Virus-Cell Interaction Section, HIV Drug Resistance Program National Cancer Institute Frederick, MD 21702
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Bhakta SJ, Shang L, Prince JL, Claiborne DT, Hunter E. Mutagenesis of tyrosine and di-leucine motifs in the HIV-1 envelope cytoplasmic domain results in a loss of Env-mediated fusion and infectivity. Retrovirology 2011; 8:37. [PMID: 21569545 PMCID: PMC3117779 DOI: 10.1186/1742-4690-8-37] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Accepted: 05/14/2011] [Indexed: 12/30/2022] Open
Abstract
Background The gp41 component of the Human Immunodeficiency Virus (HIV) envelope glycoprotein (Env) contains a long cytoplasmic domain (CD) with multiple highly conserved tyrosine (Y) and dileucine (LL) motifs. Studies suggest that the motifs distal to major endocytosis motif (Y712HRL), located at residues 712-715 of Env, may contribute to Env functionality in the viral life cycle. In order to examine the biological contribution of these motifs in the biosynthesis, transport, and function of Env, we constructed two panels of mutants in which the conserved Y- and LL-motifs were sequentially substituted by alternative residues, either in the presence or absence of Y712. Additional mutants targeting individual motifs were then constructed. Results All mutant Envs, when expressed in the absence of other viral proteins, maintained at least WT levels of Env surface staining by multiple antibodies. The Y712 mutation (Y712C) contributed to at least a 4-fold increase in surface expression for all mutants containing this change. Sequential mutagenesis of the Y- and LL-motifs resulted in a generally progressive decrease in Env fusogenicity. However, additive mutation of dileucine and tyrosine motifs beyond the tyrosine at residue 768 resulted in the most dramatic effects on Env incorporation into virions, viral infectivity, and virus fusion with target cells. Conclusions From the studies reported here, we show that mutations of the Y- and LL-motifs, which effectively eliminate the amphipathic nature of the lytic peptide 2 (LLP2) domain or disrupt YW and LL motifs in a region spanning residues 795-803 (YWWNLLQYW), just C-terminal of LLP2, can dramatically interfere with biological functions of HIV-1 Env and abrogate virus replication. Because these mutant proteins are expressed at the cell surface, we conclude that tyrosine and di-leucine residues within the cytoplasmic domain of gp41 play critical roles in HIV-1 replication that are distinct from that of targeting the plasma membrane.
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Affiliation(s)
- Sushma J Bhakta
- Emory Vaccine Center at the Yerkes National Primate Research Center and Department of Pathology and Laboratory Medicine, Emory University, Atlanta, Georgia 30329, USA
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Blay WM, Kasprzyk T, Misher L, Richardson BA, Haigwood NL. Mutations in envelope gp120 can impact proteolytic processing of the gp160 precursor and thereby affect neutralization sensitivity of human immunodeficiency virus type 1 pseudoviruses. J Virol 2007; 81:13037-49. [PMID: 17855534 PMCID: PMC2169095 DOI: 10.1128/jvi.01215-07] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The design of an efficient human immunodeficiency virus (HIV) immunogen able to generate broad neutralizing antibodies (NAbs) remains an elusive goal. As more data emerge, it is becoming apparent that one important aspect of such an immunogen will be the proper representation of the envelope protein (Env) as it exists on native virions. Important questions that are yet to be fully addressed include what factors dictate Env processing, how different Env forms are represented on the virion, and ultimately how these issues influence the development and efficacy of NAbs. Recent data have begun to illuminate the extent to which changes in gp41 can impact the overall structure and neutralizing sensitivity of Env. Here, we present evidence to suggest that minor mutations in gp120 can significantly impact Env processing. We analyzed the gp120 sequences of 20 env variants that evolved in multiple macaques over 8 months of infection with simian/human immunodeficiency virus 89.6P. Variant gp120 sequences were subcloned into gp160 expression plasmids with identical cleavage motifs and gp41 sequences. Cells cotransfected with these plasmids and delta env genomes were able to produce competent virus. The resulting pseudoviruses incorporated high levels of Env onto virions that exhibited a range of degrees of virion-associated Env cleavage (15 to 40%). Higher levels of cleavage correlated with increased infectivity and increased resistance to macaque plasma, HIV immunoglobulin, soluble CD4, and human monoclonal antibodies 4E10, 2F5, and b12. Based on these data, we discuss a model whereby changes in gp120 of 89.6P impact Env processing and thereby mediate escape from a range of neutralizing agents.
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Affiliation(s)
- Wendy M Blay
- Seattle Biomedical Research Institute, 307 Westlake Ave. N, Seattle, WA 98019, USA
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15
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Jiang J, Aiken C. Maturation-dependent human immunodeficiency virus type 1 particle fusion requires a carboxyl-terminal region of the gp41 cytoplasmic tail. J Virol 2007; 81:9999-10008. [PMID: 17609279 PMCID: PMC2045384 DOI: 10.1128/jvi.00592-07] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Lentiviruses, including human immunodeficiency virus type 1 (HIV-1), typically encode fusion glycoproteins with long cytoplasmic tails (CTs). We previously reported that immature HIV-1 particles are inhibited for fusion with target cells by a mechanism requiring the 152-amino-acid CT of gp41. The gp41 CT was also shown to mediate the detergent-resistant association of the HIV-1 envelope glycoprotein complex with immature HIV-1 particles, indicating that the gp41 CT forms a stable complex with Gag in immature virions. In the present study, we analyzed the effects of progressive truncations and point mutations in the gp41 CT on the fusion of mature and immature HIV-1 particles with target cells. We also determined the effects of these mutations on the detergent-resistant association of gp41 with immature HIV-1 particles. Removal of the C-terminal 28 amino acids relieved the dependence of HIV-1 fusion on maturation. However, a mutant Env protein lacking this region remained associated with immature HIV-1 particles treated with nonionic detergent. Further mutational analysis of the C-terminal region of gp41 revealed two specific sequences required for maturation-dependent HIV-1 fusion. Collectively, our results demonstrate that the extreme C terminus of gp41 plays a key role in coupling HIV-1 fusion competence to virion maturation. They further indicate that the stable association of gp41 with Gag in immature virions is not sufficient for inhibition of immature HIV-1 particle fusion.
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Affiliation(s)
- Jiyang Jiang
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, A-5301 Medical Center North, Nashville, TN 37232-2363, USA
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16
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Newman JT, Sturgeon TJ, Gupta P, Montelaro RC. Differential functional phenotypes of two primary HIV-1 strains resulting from homologous point mutations in the LLP domains of the envelope gp41 intracytoplasmic domain. Virology 2007; 367:102-16. [PMID: 17582453 PMCID: PMC2034414 DOI: 10.1016/j.virol.2007.05.027] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Revised: 04/09/2007] [Accepted: 05/21/2007] [Indexed: 01/10/2023]
Abstract
We previously reported that selected mutations of highly conserved arginine residues within the LLP regions of HIV-1(ME46) gp41 had diverse effects on Env function. In the current study, we sought to test if the observed LLP mutant phenotypes would be similar in HIV-1(89.6). The results of the current studies revealed that the LLP-1 mutations conferred reduced Env incorporation, infectivity, and replication phenotypes in both viruses, while homologous LLP-2 mutations had differential phenotypical effects between the two strains. In particular, several of the 89.6 LLP-2 mutant viruses were replication defective in CEMX174 cells despite having increased levels of Env incorporation, and with both strains, there were differential effects on infectivity. This comparison of homologous point mutations in two different strains of HIV supports the role of LLPs as determinants of Env function, but reveals for the first time the influence of virus strain on LLP mutant phenotypes.
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Affiliation(s)
- Jason T Newman
- Department of Molecular Genetics and Biochemistry, School of Medicine, University of Pittsburgh, PA 15261, USA
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17
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Celma CCP, Paladino MG, González SA, Affranchino JL. Importance of the short cytoplasmic domain of the feline immunodeficiency virus transmembrane glycoprotein for fusion activity and envelope glycoprotein incorporation into virions. Virology 2007; 366:405-14. [PMID: 17559903 DOI: 10.1016/j.virol.2007.05.019] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2007] [Revised: 04/25/2007] [Accepted: 05/14/2007] [Indexed: 11/28/2022]
Abstract
The mature form of the envelope (Env) glycoprotein of lentiviruses is a heterodimer composed of the surface (SU) and transmembrane (TM) subunits. Feline immunodeficiency virus (FIV) possesses a TM glycoprotein with a cytoplasmic tail of approximately 53 amino acids which is unusually short compared with that of the other lentiviral glycoproteins (more than 100 residues). To investigate the relevance of the FIV TM cytoplasmic domain to Env-mediated viral functions, we characterized the biological properties of a series of Env glycoproteins progressively shortened from the carboxyl terminus. All the mutant Env proteins were efficiently expressed in feline cells and processed into the SU and TM subunits. Deletion of 5 or 11 amino acids from the TM C-terminus did not significantly affect Env surface expression, fusogenic activity or Env incorporation into virions, whereas removal of 17 or 23 residues impaired Env-mediated cell-to-cell fusion. Further truncation of the FIV TM by 29 residues resulted in an Env glycoprotein that was poorly expressed at the cell surface, exhibited only 20% of the wild-type Env fusogenic capacity and was inefficiently incorporated into virions. Remarkably, deletion of the TM C-terminal 35 or 41 amino acids restored or even enhanced Env biological functions. Indeed, these mutant Env glycoproteins bearing cytoplasmic domains of 18 or 12 amino acids were found to be significantly more fusogenic than the wild-type Env and were efficiently incorporated into virions. Interestingly, truncation of the TM cytoplasmic domain to only 6 amino acids did not affect Env incorporation into virions but abrogated Env fusogenicity. Finally, removal of the entire TM cytoplasmic tail or deletion of as many as 6 amino acids into the membrane-spanning domain led to a complete loss of Env functions. Our results demonstrate that despite its relatively short length, the FIV TM cytoplasmic domain plays an important role in modulating Env-mediated viral functions.
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Affiliation(s)
- Cristina C P Celma
- Laboratorio de Virología, Facultad de Ciencias Exactas y Naturales, Universidad de Belgrano (UB), Villanueva 1324 (C1426BMJ), Buenos Aires, Argentina
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18
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Day JR, Van Damme N, Guatelli JC. The effect of the membrane-proximal tyrosine-based sorting signal of HIV-1 gp41 on viral infectivity depends on sequences within gp120. Virology 2006; 354:316-27. [PMID: 16905171 DOI: 10.1016/j.virol.2006.06.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2006] [Revised: 05/11/2006] [Accepted: 06/19/2006] [Indexed: 11/28/2022]
Abstract
The cytoplasmic domain of the HIV-1 Env glycoprotein (gp41) contains sequences that affect the trafficking of Env within the host cell. We previously showed that the membrane-proximal tyrosine-based adaptor protein (AP)-binding signal of gp41 (Y712XXL) is required for optimal viral infectivity and entry into target cells. Because these effects were not attributable to an effect on the incorporation of Env into virions, we hypothesized that they involved targeting of viral assembly to specific endosomal membranes that conferred greater fusogenicity. To further elaborate this hypothesis, we mutated the C-terminal leucine-based AP-binding signal of gp41 (LL855/856). In contrast to Env Y712, the leucine signal was dispensable for viral infectivity in both single cycle assays and during spreading infections within cultures of peripheral blood mononuclear cells (PBMCs). To test the hypothesis that these AP-binding motifs target Env to endosomes during viral morphogenesis, we compared the subcellular localization of wild-type Env to mutants of the Y712 and LL855/856 signals. The results failed to support the hypothesis that these signals target viral assembly to specific endosomal membranes. Strikingly, in the context of a C2-V3 region that confers macrophage-tropism, mutation of Y712 no longer markedly affected viral infectivity in either single cycle assays or during spreading infection within PBMCs, and it did not impair viral entry. These data indicate that the importance of the tyrosine-based sorting signal in gp41 for optimal viral infectivity depends on sequences in gp120. This observation is consistent with the hypothesis that the Y712 residue is part of the ectodomain of gp41 in virion-associated Env. We speculate that as part of the ectodomain, Y712 could affect specifically the conformation of the more positively charged CXCR4-tropic V3 loop in a manner that augments viral fusogenicity and infectivity.
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Affiliation(s)
- John R Day
- Department of Pathology, University of California San Diego, San Diego, CA, USA.
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