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Elucidating the Basis for Permissivity of the MT-4 T-Cell Line to Replication of an HIV-1 Mutant Lacking the gp41 Cytoplasmic Tail. J Virol 2020; 94:JVI.01334-20. [PMID: 32938764 DOI: 10.1128/jvi.01334-20] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 09/07/2020] [Indexed: 12/11/2022] Open
Abstract
HIV-1 encodes an envelope glycoprotein (Env) that contains a long cytoplasmic tail (CT) harboring trafficking motifs implicated in Env incorporation into virus particles and viral transmission. In most physiologically relevant cell types, the gp41 CT is required for HIV-1 replication, but in the MT-4 T-cell line the gp41 CT is not required for a spreading infection. To help elucidate the role of the gp41 CT in HIV-1 transmission, in this study, we investigated the viral and cellular factors that contribute to the permissivity of MT-4 cells to gp41 CT truncation. We found that the kinetics of HIV-1 production and virus release are faster in MT-4 than in the other T-cell lines tested, but MT-4 cells express equivalent amounts of HIV-1 proteins on a per-cell basis relative to cells not permissive to CT truncation. MT-4 cells express higher levels of plasma-membrane-associated Env than nonpermissive cells, and Env internalization from the plasma membrane is less efficient than that from another T-cell line, SupT1. Paradoxically, despite the high levels of Env on the surface of MT-4 cells, 2-fold less Env is incorporated into virus particles produced from MT-4 than SupT1 cells. Contact-dependent transmission between cocultured 293T and MT-4 cells is higher than in cocultures of 293T with most other T-cell lines tested, indicating that MT-4 cells are highly susceptible to cell-to-cell infection. These data help to clarify the long-standing question of how MT-4 cells overcome the requirement for the HIV-1 gp41 CT and support a role for gp41 CT-dependent trafficking in Env incorporation and cell-to-cell transmission in physiologically relevant cell lines.IMPORTANCE The HIV-1 Env cytoplasmic tail (CT) is required for efficient Env incorporation into nascent particles and viral transmission in primary CD4+ T cells. The MT-4 T-cell line has been reported to support multiple rounds of infection of HIV-1 encoding a gp41 CT truncation. Uncovering the underlying mechanism of MT-4 T-cell line permissivity to gp41 CT truncation would provide key insights into the role of the gp41 CT in HIV-1 transmission. This study reveals that multiple factors contribute to the unique ability of a gp41 CT truncation mutant to spread in cultures of MT-4 cells. The lack of a requirement for the gp41 CT in MT-4 cells is associated with the combined effects of rapid HIV-1 protein production, high levels of cell-surface Env expression, and increased susceptibility to cell-to-cell transmission compared to nonpermissive cells.
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Range of CD4-Bound Conformations of HIV-1 gp120, as Defined Using Conditional CD4-Induced Antibodies. J Virol 2016; 90:4481-4493. [PMID: 26889042 DOI: 10.1128/jvi.03206-15] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Accepted: 02/14/2016] [Indexed: 01/23/2023] Open
Abstract
UNLABELLED The HIV envelope binds cellular CD4 and undergoes a range of conformational changes that lead to membrane fusion and delivery of the viral nucleocapsid into the cellular cytoplasm. This binding to CD4 reveals cryptic and highly conserved epitopes, the molecular nature of which is still not fully understood. The atomic structures of CD4 complexed with gp120 core molecules (a form of gp120 in which the V1, V2, and V3 loops and N and C termini have been truncated) have indicated that a hallmark feature of the CD4-bound conformation is the bridging sheet minidomain. Variations in the orientation of the bridging sheet hairpins have been revealed when CD4-liganded gp120 was compared to CD4-unliganded trimeric envelope structures. Hence, there appears to be a number of conformational transitions possible in HIV-1 monomeric gp120 that are affected by CD4 binding. The spectrum of CD4-bound conformations has been interrogated in this study by using a well-characterized panel of conditional, CD4-induced (CD4i) monoclonal antibodies (MAbs) that bind HIV-1 gp120 and its mutations under various conditions. Two distinct CD4i epitopes of the outer domain were studied: the first comprises the bridging sheet, while the second contains elements of the V2 loop. Furthermore, we show that the unliganded extended monomeric core of gp120 (coree) assumes an intermediate CD4i conformation in solution that further undergoes detectable rearrangements upon association with CD4. These discoveries impact both accepted paradigms concerning gp120 structure and the field of HIV immunogen design. IMPORTANCE Elucidation of the conformational transitions that the HIV-1 envelope protein undergoes during the course of entry into CD4(+)cells is fundamental to our understanding of HIV biology. The binding of CD4 triggers a range of gp120 structural rearrangements that could present targets for future drug design and development of preventive vaccines. Here we have systematically interrogated and scrutinized these conformational transitions using a panel of antibody probes that share a specific preference for the CD4i conformations. These have been employed to study a collection of gp120 mutations and truncations. Through these analyses, we propose 4 distinct sequential steps in CD4i transitions of gp120 conformations, each defined by antibody specificities and structural requirements of the HIV envelope monomer. As a result, we not only provide new insights into this dynamic process but also define probes to further investigate HIV infection.
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Conformational characterization of aberrant disulfide-linked HIV-1 gp120 dimers secreted from overexpressing cells. J Virol Methods 2010; 168:155-61. [PMID: 20471426 DOI: 10.1016/j.jviromet.2010.05.008] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Revised: 04/01/2010] [Accepted: 05/06/2010] [Indexed: 11/23/2022]
Abstract
The envelope (Env) glycoproteins of human immunodeficiency virus (HIV-1) mediate viral entry and are also the primary target of neutralizing antibodies. The gp160 envelope glycoprotein precursor undergoes proteolytic cleavage in the Golgi complex to produce the gp120 exterior glycoprotein and the gp41 transmembrane glycoprotein, which remain associated non-covalently in the trimeric Env complex. Monomeric soluble gp120 has been used extensively to investigate conformational states, structure, antigenicity and immunogenicity of the HIV-1 Env glycoproteins. Expression of gp120 alone (without gp41) leads to the accumulation not only of monomeric gp120 but also an aberrant dimeric form. The gp120 dimers were sensitive to reducing agents. The formation of gp120 dimers was disrupted by a single amino acid change in the inner domain, and was reduced by removal of the V1/V2 variable loops or the N and C termini. Epitopes on the gp120 inner domain and the chemokine receptor-binding surface were altered or occluded by gp120 dimerization. Awareness of the existence and properties of gp120 dimers should assist interpretation of studies of this key viral protein.
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Ou W, Silver J. Efficient trapping of HIV-1 envelope protein by hetero-oligomerization with an N-helix chimera. Retrovirology 2005; 2:51. [PMID: 16092970 PMCID: PMC1199619 DOI: 10.1186/1742-4690-2-51] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2005] [Accepted: 08/10/2005] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND The N-heptad repeat region of the HIV-1 Transmembrane Envelope protein is a trimerization domain that forms part of a "six helix bundle" crucial to Envelope-mediated membrane fusion. N-heptad repeat peptides have been used as extracellular reagents to inhibit virus fusion. RESULTS When expressed intracellularly with wild-type HIV-1 Envelope protein, the N-heptad repeat domain efficiently hetero-oligomerized with Envelope and trapped it in the endoplasmic reticulum or early Golgi, as indicated by lack of transport to the cell surface, absent proteolytic processing, and aberrant glycosylation. CONCLUSION Post-translational processing of HIV Envelope is very sensitive to an agent that binds to the N-heptad repeat during synthesis, suggesting that it might be possible to modify drugs that bind to this region to have transport-blocking properties.
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Affiliation(s)
- Wu Ou
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Building 4, Room 336, Bethesda, MD 20892, USA
| | - Jonathan Silver
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Building 4, Room 336, Bethesda, MD 20892, USA
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5
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Center RJ, Lebowitz J, Leapman RD, Moss B. Promoting trimerization of soluble human immunodeficiency virus type 1 (HIV-1) Env through the use of HIV-1/simian immunodeficiency virus chimeras. J Virol 2004; 78:2265-76. [PMID: 14963123 PMCID: PMC369220 DOI: 10.1128/jvi.78.5.2265-2276.2004] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The envelope proteins (Env) of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) form homo-oligomers in the endoplasmic reticulum. The oligomeric structure of Env is maintained, but is less stable, after cleavage in a Golgi compartment and transport to the surface of infected cells. Functional, virion-associated HIV-1 and SIV Env have an almost exclusively trimeric structure. In addition, a soluble form of SIV Env (gp140) forms a nearly homogeneous population of trimers. Here, we describe the oligomeric structure of soluble, uncleaved HIV-1 gp140 and modifications that promote a stable trimeric structure. Biochemical and biophysical analyses, including sedimentation equilibrium and scanning transmission electron microscopy, revealed that unmodified HIV-1 gp140 purified as a heterogeneous range of oligomeric species, including dimers and aggregates. Deletion of the V2 domain alone or, especially, both the V1 and V2 domains reduced dimer formation but promoted aggregation rather than trimerization. Expressing gp140 with mannose-only oligosaccharides did not eliminate heterogeneity. Replacement of the entire gp41 segment of HIV-1 gp140 or just the N-terminal half (85 amino acids) of this segment with the corresponding region of SIV was sufficient to confer efficient trimerization for gp140 derived from clade B and C isolates. Importantly, the relatively small segment of the HIV Env replaced by SIV sequences contains no known targets of neutralizing antibody. The soluble trimeric form of HIV-1 Env should prove useful for assessment of antigenic structure and immunogenicity.
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MESH Headings
- Chromatography, Gel
- Dimerization
- Gene Products, env/chemistry
- Gene Products, env/genetics
- Gene Products, env/metabolism
- Gene Products, env/ultrastructure
- HIV Envelope Protein gp41/chemistry
- HIV Envelope Protein gp41/genetics
- HIV Envelope Protein gp41/metabolism
- HIV-1/chemistry
- Mannose/analysis
- Microscopy, Electron, Scanning Transmission
- Molecular Weight
- Protein Structure, Quaternary
- Protein Structure, Tertiary
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Sequence Deletion
- Simian Immunodeficiency Virus/chemistry
- Solubility
- env Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
- Rob J Center
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
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6
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Center RJ, Leapman RD, Lebowitz J, Arthur LO, Earl PL, Moss B. Oligomeric structure of the human immunodeficiency virus type 1 envelope protein on the virion surface. J Virol 2002; 76:7863-7. [PMID: 12097599 PMCID: PMC136379 DOI: 10.1128/jvi.76.15.7863-7867.2002] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The envelope protein (Env) of human immunodeficiency virus type 1 forms homo-oligomers in the endoplasmic reticulum. The oligomeric structure of Env is maintained after cleavage in a Golgi compartment and transport to the surfaces of infected cells, where incorporation into budding virions takes place. Here, we use biophysical techniques to assess the oligomeric valency of virion-associated Env prior to fusion activation. Virion-associated Env oligomers were stabilized by chemical cross-linking prior to detergent extraction and were purified by immunoaffinity chromatography. Gel filtration revealed a single predominant oligomeric species, and sedimentation equilibrium analysis-derived mass values indicated a trimeric structure. Determination of the masses of individual Env molecules by scanning transmission electron microscopy demonstrated that virion-associated Env was trimeric, and a triangular morphology was observed in 20 to 30% of the molecules. These results, which firmly establish the oligomeric structure of human immunodeficiency virus virion-associated Env, parallel those of our previous analysis of the simian immunodeficiency virus Env.
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Affiliation(s)
- Rob J Center
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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Lewicki DN, Gallagher TM. Quaternary structure of coronavirus spikes in complex with carcinoembryonic antigen-related cell adhesion molecule cellular receptors. J Biol Chem 2002; 277:19727-34. [PMID: 11912215 PMCID: PMC8060896 DOI: 10.1074/jbc.m201837200] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Oligomeric spike (S) glycoproteins extend from coronavirus membranes. These integral membrane proteins assemble within the endoplasmic reticulum of infected cells and are subsequently endoproteolyzed in the Golgi, generating noncovalently associated S1 and S2 fragments. Once on the surface of infected cells and virions, peripheral S1 fragments bind carcinoembryonic antigen-related cell adhesion molecule (CEACAM) receptors, and this triggers membrane fusion reactions mediated by integral membrane S2 fragments. We focused on the quaternary structure of S and its interaction with CEACAMs. We discovered that soluble S1 fragments were dimers and that CEACAM binding was entirely dependent on this quaternary structure. However, two differentially tagged CEACAMs could not co-precipitate with the S dimers, suggesting that binding sites were closely juxtaposed in the dimer (steric hindrance) or that a single CEACAM generated global conformational changes that precluded additional interactions (negative cooperativity). CEACAM binding did indeed alter S1 conformations, generating alternative disulfide linkages that were revealed on SDS gels. CEACAM binding also induced separation of S1 and S2. Differentially tagged S2 fragments that were free of S1 dimers were not co-precipitated, suggesting that S1 harbored the primary oligomerization determinants. We discuss the distinctions between the S.CEACAM interaction and other virus-receptor complexes involved in receptor-triggered entry.
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Affiliation(s)
- Daniel N Lewicki
- Department of Microbiology and Immunology, Loyola University Medical Center, Maywood, Illinois 60153, USA
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Le Blanc I, Grange MP, Delamarre L, Rosenberg AR, Blot V, Pique C, Dokhélar MC. HTLV-1 structural proteins. Virus Res 2001; 78:5-16. [PMID: 11520576 DOI: 10.1016/s0168-1702(01)00278-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
HTLV-1 structural proteins do not appear to ensure virus transmission as efficiently as most other retrovirus structural proteins do, whereas all other retroviruses can be transmitted via either free virions or cell-to-cell contacts, infection by HTLV-1 by free virions is very inefficient, and effective infection requires the presence of HTLV-1 infected cells. This characteristic feature of HTLV-1 provides a unique tool which can be used to analyse retrovirus cellular transmission in the absence of simultaneous cell-free infection. Here we summarise what is known about HTLV-1 structural proteins and identify the questions about these proteins which remain to be answered.
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Affiliation(s)
- I Le Blanc
- INSERM U332, Institut Cochin de Génétique Moléculaire, 22 Rue Méchain, 75014, Paris, France
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Cho MW. Assessment of HIV vaccine development: past, present, and future. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2001; 49:263-314. [PMID: 11013767 DOI: 10.1016/s1054-3589(00)49030-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Affiliation(s)
- M W Cho
- AIDS Vaccine Research and Development Unit, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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10
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Chen B, Zhou G, Kim M, Chishti Y, Hussey RE, Ely B, Skehel JJ, Reinherz EL, Harrison SC, Wiley DC. Expression, purification, and characterization of gp160e, the soluble, trimeric ectodomain of the simian immunodeficiency virus envelope glycoprotein, gp160. J Biol Chem 2000; 275:34946-53. [PMID: 10944528 DOI: 10.1074/jbc.m004905200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The envelope glycoprotein, gp160, of simian immunodeficiency virus (SIV) shares approximately 25% sequence identity with gp160 from the human immunodeficiency virus, type I, indicating a close structural similarity. As a result of binding to cell surface CD4 and co-receptor (e.g. CCR5 and CXCR4), both SIV and human immunodeficiency virus gp160 mediate viral entry by membrane fusion. We report here the characterization of gp160e, the soluble ectodomain of SIV gp160. The ectodomain has been expressed in both insect cells and Chinese hamster ovary (CHO)-Lec3.2.8.1 cells, deficient in enzymes necessary for synthesizing complex oligosaccharides. Both the primary and a secondary proteolytic cleavage sites between the gp120 and gp41 subunits of gp160 were mutated to prevent cleavage and shedding of gp120. The purified, soluble glycoprotein is shown to be trimeric by chemical cross-linking, gel filtration chromatography, and analytical ultracentrifugation. It forms soluble, tight complexes with soluble CD4 and a number of Fab fragments from neutralizing monoclonal antibodies. Soluble complexes were also produced of enzymatically deglycosylated gp160e and of gp160e variants with deletions in the variable segments.
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MESH Headings
- Animals
- Antibodies, Monoclonal/metabolism
- CD4 Antigens/metabolism
- CHO Cells
- Cell Line
- Chromatography, Gel
- Circular Dichroism
- Cricetinae
- Cross-Linking Reagents
- Electrophoresis, Polyacrylamide Gel
- Gene Deletion
- Gene Products, env/chemistry
- Gene Products, env/genetics
- Gene Products, env/isolation & purification
- Gene Products, env/metabolism
- Glycosylation
- Insecta
- Models, Genetic
- Mutagenesis, Site-Directed
- Protein Binding
- Protein Structure, Tertiary
- Ultracentrifugation
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Affiliation(s)
- B Chen
- Laboratory of Molecular Medicine, The Children's Hospital, Howard Hughes Medical Institute, Boston, Massachusetts 02215, USA
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11
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Center RJ, Earl PL, Lebowitz J, Schuck P, Moss B. The human immunodeficiency virus type 1 gp120 V2 domain mediates gp41-independent intersubunit contacts. J Virol 2000; 74:4448-55. [PMID: 10775580 PMCID: PMC111965 DOI: 10.1128/jvi.74.10.4448-4455.2000] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The envelope protein of human immunodeficiency virus type 1 HIV-1 undergoes proteolytic cleavage in the Golgi complex to produce subunits designated gp120 and gp41, which remain noncovalently associated. While gp41 has a well-characterized oligomeric structure, the maintenance of gp41-independent gp120 intersubunit contacts remains a contentious issue. Using recombinant vaccinia virus to achieve high-level expression of gp120 in mammalian cells combined with gel filtration analysis, we were able to isolate a discrete oligomeric form of gp120. Oligomerization of gp120 occurred intracellularly between 30 and 120 min after synthesis. Analysis by sedimentation equilibrium unequivocally identified the oligomeric species as a dimer. In order to identify the domains involved in the intersubunit contact, we expressed a series of gp120 proteins lacking various domains and assessed the effects of mutation on oligomeric structure. Deletion of the V1 or V3 loops had little effect on the relative amounts of monomer and dimer in comparison to wild-type gp120. In contrast, deletion of either all or part of the V2 loop drastically reduced dimer formation, indicating that this domain is required for intersubunit contact formation. Consistent with this, the V2 loop of the dimer was less accessible than that of the monomer to a specific monoclonal antibody. Previous studies have shown that while the V2 loop is not an absolute requirement for viral entry, the absence of this domain reduces viral resistance to neutralization by monoclonal antibodies or sera. We propose that the quaternary structure of gp120 may contribute to resistance to neutralization by limiting the exposure of conserved epitopes.
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Affiliation(s)
- R J Center
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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12
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Rencher SD, Hurwitz JL. Effect of natural HIV-1 envelope V1-V2 sequence diversity on the binding of V3-specific and non-V3-specific antibodies. JOURNAL OF ACQUIRED IMMUNE DEFICIENCY SYNDROMES AND HUMAN RETROVIROLOGY : OFFICIAL PUBLICATION OF THE INTERNATIONAL RETROVIROLOGY ASSOCIATION 1997; 16:69-73. [PMID: 9358100 DOI: 10.1097/00042560-199710010-00001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In past years, much attention has been paid to the HIV-1 envelope (env) protein variable region 3 (V3), termed the principal neutralizing determinant. HIV-1 vaccines were often designed to target V3, and vaccine efficacy was often measured with V3-based assays. Thus, some disappointment resulted when volunteers in first clinical vaccine trials generated V3-specific antibodies that could not protect against V3-similar viruses. We describe an analysis of V1 and V2 sequence effects on antibody binding to V3 and non-V3 determinants. This study involved the preparation of seven full-length (gp160), chimeric env proteins in a vaccinia virus (VV) expression system. Chimeric proteins displayed different V1-V2 sequences but were otherwise identical. A panel of 12 monoclonal antibodies was then tested for binding activities toward the seven chimeras. Results showed that V1-V2 sequences affected antibody binding to env, both in V3 and non-V3 positions. These data demonstrate the enormous complexity of HIV-1 env protein conformation and antigenic determinants. Respect for the complexity of antibody-antigen interactions encourages the design of sophisticated immunoglobulin and protein cocktails for use in HIV-1 therapies and vaccines, respectively.
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Affiliation(s)
- S D Rencher
- Department of Immunology, St. Jude Children's Research Hospital, University of Memphis, Tennessee, U.S.A
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Andeweg AC, Groenink M, Leeflang P, de Goede RE, Osterhaus AD, Tersmette M, Bosch ML. Genetic and functional analysis of a set of HIV-1 envelope genes obtained from biological clones with varying syncytium-inducing capacities. AIDS Res Hum Retroviruses 1992; 8:1803-13. [PMID: 1457193 DOI: 10.1089/aid.1992.8.1803] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
To study HIV-1 envelope-mediated syncytium formation we have amplified, cloned, expressed, and sequenced individual envelope genes from a set of eight biological HIV-1 clones. These clones were obtained from two patients and display either a syncytium-inducing (SI) or nonsyncytium-inducing (NSI) phenotype. Upon expression through recombinant vaccinia virus, individual envelope gene products display heterogeneous syncytium-inducing capacities which reflect the phenotype of the parental biological HIV-1 clones in all cases. For the eight biological HIV-1 clones presented here, variation of the envelope gene alone is sufficient to explain the observed variable syncytium-inducing capacity of the respective parental viruses. In addition we determined the complete nucleotide sequence of these envelope genes. The predicted amino acid sequence revealed a considerable amount of variation located mainly in the previously denominated variable regions. In various regions of envelope genes obtained from the same patient, phenotype associated amino acid variation was found. This phenotype associated amino acid variation however, is not conserved between the two sets of envelope genes derived from different patients. Four envelope sequences derived from clones obtained from one patient showed phenotype-associated amino acid variation in the fusion domain. Sequencing of 12 additional fusion domains revealed that this same variation is found in four additional clones. However, a functional test performed on recombinant vaccinia expressing mutant envelope genes showed that this observed fusion domain variation does not contribute to the variation in syncytium-inducing capacity of the envelope gene product.
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Affiliation(s)
- A C Andeweg
- Laboratory of Immunobiology, National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands
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