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Viral and Host Factors Regulating HIV-1 Envelope Protein Trafficking and Particle Incorporation. Viruses 2022; 14:v14081729. [PMID: 36016351 PMCID: PMC9415270 DOI: 10.3390/v14081729] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 07/25/2022] [Accepted: 08/02/2022] [Indexed: 11/17/2022] Open
Abstract
The HIV-1 envelope glycoprotein (Env) is an essential structural component of the virus, serving as the receptor-binding protein and principal neutralizing determinant. Env trimers are incorporated into developing particles at the plasma membrane of infected cells. Incorporation of HIV-1 Env into particles in T cells and macrophages is regulated by the long Env cytoplasmic tail (CT) and the matrix region of Gag. The CT incorporates motifs that interact with cellular factors involved in endosomal trafficking. Env follows an unusual pathway to arrive at the site of particle assembly, first traversing the secretory pathway to the plasma membrane (PM), then undergoing endocytosis, followed by directed sorting to the site of particle assembly on the PM. Many aspects of Env trafficking remain to be defined, including the sequential events that occur following endocytosis, leading to productive recycling and particle incorporation. This review focuses on the host factors and pathways involved in Env trafficking, and discusses leading models of Env incorporation into particles.
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2
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McCaul N, Quandte M, Bontjer I, van Zadelhoff G, Land A, Crooks ET, Binley JM, Sanders RW, Braakman I. Intramolecular quality control: HIV-1 envelope gp160 signal-peptide cleavage as a functional folding checkpoint. Cell Rep 2021; 36:109646. [PMID: 34469718 DOI: 10.1016/j.celrep.2021.109646] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Revised: 06/28/2021] [Accepted: 08/11/2021] [Indexed: 11/24/2022] Open
Abstract
Removal of the membrane-tethering signal peptides that target secretory proteins to the endoplasmic reticulum is a prerequisite for proper folding. While generally thought to be removed co-translationally, we report two additional post-targeting functions for the HIV-1 gp120 signal peptide, which remains attached until gp120 folding triggers its removal. First, the signal peptide improves folding fidelity by enhancing conformational plasticity of gp120 by driving disulfide isomerization through a redox-active cysteine. Simultaneously, the signal peptide delays folding by tethering the N terminus to the membrane, until assembly with the C terminus. Second, its carefully timed cleavage represents intramolecular quality control and ensures release of (only) natively folded gp120. Postponed cleavage and the redox-active cysteine are both highly conserved and important for viral fitness. Considering the ∼15% proteins with signal peptides and the frequency of N-to-C contacts in protein structures, these regulatory roles of signal peptides are bound to be more common in secretory-protein biogenesis.
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Affiliation(s)
- Nicholas McCaul
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Science4Life, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, the Netherlands
| | - Matthias Quandte
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Science4Life, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, the Netherlands
| | - Ilja Bontjer
- Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam Institute for Infection and Immunity, 1105 Amsterdam, the Netherlands
| | - Guus van Zadelhoff
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Science4Life, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, the Netherlands
| | - Aafke Land
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Science4Life, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, the Netherlands
| | - Ema T Crooks
- San Diego Biomedical Research Institute, 10865 Road to the Cure #100, San Diego, CA, USA
| | - James M Binley
- San Diego Biomedical Research Institute, 10865 Road to the Cure #100, San Diego, CA, USA
| | - Rogier W Sanders
- Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam Institute for Infection and Immunity, 1105 Amsterdam, the Netherlands; Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, NY 10021, USA
| | - Ineke Braakman
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Science4Life, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, the Netherlands.
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3
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Characteristics of HIV-1 env genes from Chinese chronically infected donors with highly broad cross-neutralizing activity. Virology 2020; 551:16-25. [PMID: 33010671 DOI: 10.1016/j.virol.2020.08.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 08/17/2020] [Accepted: 08/23/2020] [Indexed: 11/24/2022]
Abstract
Knowledge about the special characteristics of HIV-1 envelope (env) glycoproteins in rare individuals developing >90% neutralization breadth in Chinese subtype B' slow progressors may provide insights for vaccine design against local viruses. We performed a cross-sectional analysis on 7 samples. We tested the neutralization breadth and geometric mean ID50 titers (GMTs) of these samples, and divided them into hBCN+ and hBCN- group according to whether their neutralization breadth >90%. We obtained env sequences in these samples through single genome amplification (SGA) assay. By comparing with hBCN-, subtype B chronically infected group (B-SP), and Chinese subtype B group (B-Database), we analyzed the characteristics of the env sequences of hBCN+ group. Longer V1 and V4 regions with more glycosylation sites were found in hBCN+ samples compared to hBCN- samples. Further analysis compared to B-SP and B-Database showed that hBCN+ group exhibited unique extra-long V1 region containing higher proportion of N-glycan sites and additional cysteines.
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4
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Schommers P, Gruell H, Abernathy ME, Tran MK, Dingens AS, Gristick HB, Barnes CO, Schoofs T, Schlotz M, Vanshylla K, Kreer C, Weiland D, Holtick U, Scheid C, Valter MM, van Gils MJ, Sanders RW, Vehreschild JJ, Cornely OA, Lehmann C, Fätkenheuer G, Seaman MS, Bloom JD, Bjorkman PJ, Klein F. Restriction of HIV-1 Escape by a Highly Broad and Potent Neutralizing Antibody. Cell 2020; 180:471-489.e22. [PMID: 32004464 PMCID: PMC7042716 DOI: 10.1016/j.cell.2020.01.010] [Citation(s) in RCA: 90] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Revised: 12/05/2019] [Accepted: 01/06/2020] [Indexed: 02/07/2023]
Abstract
Broadly neutralizing antibodies (bNAbs) represent a promising approach to prevent and treat HIV-1 infection. However, viral escape through mutation of the HIV-1 envelope glycoprotein (Env) limits clinical applications. Here we describe 1-18, a new VH1-46-encoded CD4 binding site (CD4bs) bNAb with outstanding breadth (97%) and potency (GeoMean IC50 = 0.048 μg/mL). Notably, 1-18 is not susceptible to typical CD4bs escape mutations and effectively overcomes HIV-1 resistance to other CD4bs bNAbs. Moreover, mutational antigenic profiling uncovered restricted pathways of HIV-1 escape. Of most promise for therapeutic use, even 1-18 alone fully suppressed viremia in HIV-1-infected humanized mice without selecting for resistant viral variants. A 2.5-Å cryo-EM structure of a 1-18-BG505SOSIP.664 Env complex revealed that these characteristics are likely facilitated by a heavy-chain insertion and increased inter-protomer contacts. The ability of 1-18 to effectively restrict HIV-1 escape pathways provides a new option to successfully prevent and treat HIV-1 infection.
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Affiliation(s)
- Philipp Schommers
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany; Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany; German Center for Infection Research (DZIF), partner site Bonn-Cologne, 50931 Cologne, Germany
| | - Henning Gruell
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany; German Center for Infection Research (DZIF), partner site Bonn-Cologne, 50931 Cologne, Germany
| | - Morgan E Abernathy
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - My-Kim Tran
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany
| | - Adam S Dingens
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
| | - Harry B Gristick
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Christopher O Barnes
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Till Schoofs
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany
| | - Maike Schlotz
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany
| | - Kanika Vanshylla
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany
| | - Christoph Kreer
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany
| | - Daniela Weiland
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany
| | - Udo Holtick
- Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany
| | - Christof Scheid
- Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany
| | - Markus M Valter
- Department of Gynecology and Obstetrics, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany
| | - Marit J van Gils
- Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, 1105 AZ Amsterdam, the Netherlands
| | - Rogier W Sanders
- Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, 1105 AZ Amsterdam, the Netherlands; Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, NY 10021, USA
| | - Jörg J Vehreschild
- Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany; German Center for Infection Research (DZIF), partner site Bonn-Cologne, 50931 Cologne, Germany; Medical Department 2, University Hospital of Frankfurt, 60590 Frankfurt, Germany
| | - Oliver A Cornely
- Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany; German Center for Infection Research (DZIF), partner site Bonn-Cologne, 50931 Cologne, Germany; Clinical Trials Centre Cologne (ZKS Köln), University of Cologne, 50935 Cologne, Germany; Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, 50931 Cologne, Germany; Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany
| | - Clara Lehmann
- Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany; German Center for Infection Research (DZIF), partner site Bonn-Cologne, 50931 Cologne, Germany; Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany
| | - Gerd Fätkenheuer
- Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany; German Center for Infection Research (DZIF), partner site Bonn-Cologne, 50931 Cologne, Germany
| | - Michael S Seaman
- Center for Virology and Vaccine Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
| | - Jesse D Bloom
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA; Howard Hughes Medical Institute, Seattle, WA 98109, USA
| | - Pamela J Bjorkman
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Florian Klein
- Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany; German Center for Infection Research (DZIF), partner site Bonn-Cologne, 50931 Cologne, Germany; Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany.
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5
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de Taeye SW, Go EP, Sliepen K, de la Peña AT, Badal K, Medina-Ramírez M, Lee WH, Desaire H, Wilson IA, Moore JP, Ward AB, Sanders RW. Stabilization of the V2 loop improves the presentation of V2 loop-associated broadly neutralizing antibody epitopes on HIV-1 envelope trimers. J Biol Chem 2019; 294:5616-5631. [PMID: 30728245 PMCID: PMC6462529 DOI: 10.1074/jbc.ra118.005396] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 01/15/2019] [Indexed: 11/16/2022] Open
Abstract
A successful HIV-1 vaccine will likely need to elicit broadly neutralizing antibodies (bNAbs) that target the envelope glycoprotein (Env) spike on the virus. Native-like recombinant Env trimers of the SOSIP design now serve as a platform for achieving this challenging goal. However, SOSIP trimers usually do not bind efficiently to the inferred germline precursors of bNAbs (gl-bNAbs). We hypothesized that the inherent flexibilities of the V1 and V2 variable loops in the Env trimer contribute to the poor recognition of gl-bNAb epitopes at the trimer apex that extensively involve V2 residues. To reduce local V2 flexibility and improve the binding of V2-dependent bNAbs and gl-bNAbs, we designed BG505 SOSIP.664 trimer variants containing newly created disulfide bonds intended to stabilize the V2 loop in an optimally antigenic configuration. The first variant, I184C/E190C, contained a new disulfide bond within the V2 loop, whereas the second variant, E153C/R178C, had a new disulfide bond that cross-linked V2 and V1. The resulting engineered native-like trimer variants were both more reactive with and were neutralized by V2 bNAbs and gl-bNAbs, a finding that may be valuable in the design of germline targeting and boosting trimer immunogens to create an antigenic conformation optimal for HIV vaccine development.
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Affiliation(s)
- Steven W de Taeye
- From the Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands
| | - Eden P Go
- the Department of Chemistry, University of Kansas, Lawrence, Kansas 66045
| | - Kwinten Sliepen
- From the Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands
| | - Alba Torrents de la Peña
- From the Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands
| | - Kimberly Badal
- From the Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands
| | - Max Medina-Ramírez
- From the Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands
| | - Wen-Hsin Lee
- the Department of Integrative Structural and Computational Biology, Scripps CHAVI-ID, IAVI Neutralizing Antibody Center and Collaboration for AIDS Vaccine Discovery, The Scripps Research Institute, La Jolla, California 92037, and
| | - Heather Desaire
- the Department of Chemistry, University of Kansas, Lawrence, Kansas 66045
| | - Ian A Wilson
- the Department of Integrative Structural and Computational Biology, Scripps CHAVI-ID, IAVI Neutralizing Antibody Center and Collaboration for AIDS Vaccine Discovery, The Scripps Research Institute, La Jolla, California 92037, and
| | - John P Moore
- the Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10021
| | - Andrew B Ward
- the Department of Integrative Structural and Computational Biology, Scripps CHAVI-ID, IAVI Neutralizing Antibody Center and Collaboration for AIDS Vaccine Discovery, The Scripps Research Institute, La Jolla, California 92037, and
| | - Rogier W Sanders
- From the Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands, .,the Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10021
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6
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Sepúlveda-Crespo D, de la Mata FJ, Gómez R, Muñoz-Fernández MA. Sulfonate-ended carbosilane dendrimers with a flexible scaffold cause inactivation of HIV-1 virions and gp120 shedding. NANOSCALE 2018; 10:8998-9011. [PMID: 29726564 DOI: 10.1039/c8nr01664j] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Infection with human immunodeficiency virus type 1 (HIV-1) continues to be a global public health issue, especially in low-resource countries. Sexual transmission is responsible for the majority of HIV-1 infections worldwide. Women are more susceptible to HIV-1 acquisition than men and represent nearly 50% of the HIV-infected population. Topical vaginal microbicides that act at the earlier stages of infection offer a prevention strategy to reduce the acquisition of HIV-1. Dendrimers are nano-sized, radially symmetric molecules with a well-defined and monodisperse structure consisting of tree-like arms or branches. We perform a TZM.bl cell line-based screening of two families of carbosilane dendrimers (6 nanocompounds: G1-S12P, G2-S24P, G3-S48P, G1-C12P, G2-C24P and G3-C48P) that we have previously synthesized, containing 12, 24 or 48 sulfonate (or carboxylate) end-groups and a polyphenolic core. This work shows that second- and third-generation sulfonate-ended carbosilane dendrimers with a polyphenolic core (G2-S24P and G3-S48P, respectively) display low cytotoxicity (CC50 > 300 μM) with virucidal anti-R5-HIV-1 activity (EC50 < 50 nM; therapeutic index >6000) causing irreversible HIV-1 inactivation (80-90%) by loss of HIV-1 RNA (40%), gp120 shedding (70-80%) and p24 capsid protein release (45-60%). Herein, we demonstrate that sulfonate end-groups and a flexible scaffold from carbosilane dendrimers strongly influence their properties acting as potent virucides.
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Affiliation(s)
- Daniel Sepúlveda-Crespo
- Sección Inmunología, Laboratorio InmunoBiología Molecular, Hospital General Universitario Gregorio Marañón, Madrid 28007, Spain.
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7
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Haddox HK, Dingens AS, Hilton SK, Overbaugh J, Bloom JD. Mapping mutational effects along the evolutionary landscape of HIV envelope. eLife 2018; 7:34420. [PMID: 29590010 PMCID: PMC5910023 DOI: 10.7554/elife.34420] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2017] [Accepted: 03/15/2018] [Indexed: 01/04/2023] Open
Abstract
The immediate evolutionary space accessible to HIV is largely determined by how single amino acid mutations affect fitness. These mutational effects can shift as the virus evolves. However, the prevalence of such shifts in mutational effects remains unclear. Here, we quantify the effects on viral growth of all amino acid mutations to two HIV envelope (Env) proteins that differ at >100 residues. Most mutations similarly affect both Envs, but the amino acid preferences of a minority of sites have clearly shifted. These shifted sites usually prefer a specific amino acid in one Env, but tolerate many amino acids in the other. Surprisingly, shifts are only slightly enriched at sites that have substituted between the Envs—and many occur at residues that do not even contact substitutions. Therefore, long-range epistasis can unpredictably shift Env’s mutational tolerance during HIV evolution, although the amino acid preferences of most sites are conserved between moderately diverged viral strains. The virus that causes AIDS, or HIV, has a protein called Env on its surface, which is essential for the virus to infect cells. Env can also be recognized by the immune system, which then targets the virus for destruction or blocks it from infecting cells. Unfortunately, Env evolves very quickly, which means that HIV can evade our defenses. However, there are limits to how much this protein can change, since it still needs to perform its essential role in helping viruses enter cells. In the century since HIV first appeared in human populations, the virus has evolved considerably. There are now many HIV strains that infect people, and they bear Env proteins with substantially different sequences. However, it is not clear if these changes in sequence have resulted in Envs from distinct strains being able to tolerate different mutations. To examine this question, Haddox et al. compared how the Envs from two strains of HIV react to modifications in their sequences. They created all possible individual mutations in the proteins, and the resulting collections of mutated viruses were then tested for their ability to infect cells in the laboratory. Most mutations had similar effects in both Env proteins. This allowed Haddox et al. to identify portions of the protein that easily accommodate changes, and portions that must remain unchanged for viruses to remain infectious—at least in the laboratory. Some of these mutations are under different types of pressures when the virus faces the immune system, and those were identified using computational approaches. However, some mutations were tolerated differently by the two Env proteins. Therefore, viral strains differ in how their Env proteins can evolve. The parts of Env that showed differences in mutational tolerance between the strains were not necessarily the parts that differ in sequence. This shows that changes in sequence in one part of the protein can modify how other portions evolve. It remains to be determined whether changes in tolerance to mutations translate into differences in how the virus can escape immunity. This is an important question given that the rapid evolution of Env is a major obstacle to creating a vaccine for HIV.
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Affiliation(s)
- Hugh K Haddox
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, United States.,Molecular and Cellular Biology PhD program, University of Washington, Seattle, United States
| | - Adam S Dingens
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, United States.,Molecular and Cellular Biology PhD program, University of Washington, Seattle, United States
| | - Sarah K Hilton
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, United States.,Department of Genome Sciences, University of Washington, Seattle, United States
| | - Julie Overbaugh
- Human Biology Division, Fred Hutchinson Cancer Research Center, Seattle, United States.,Epidemiology Program, Fred Hutchinson Cancer Research Center, Seattle, United States
| | - Jesse D Bloom
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, United States.,Department of Genome Sciences, University of Washington, Seattle, United States
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Identification of Novel Structural Determinants in MW965 Env That Regulate the Neutralization Phenotype and Conformational Masking Potential of Primary HIV-1 Isolates. J Virol 2018; 92:JVI.01779-17. [PMID: 29237828 DOI: 10.1128/jvi.01779-17] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Accepted: 11/28/2017] [Indexed: 11/20/2022] Open
Abstract
The subtype C HIV-1 isolate MW965.26 is a highly neutralization-sensitive tier 1a primary isolate that is widely used in vaccine studies, but the basis for the sensitive neutralization phenotype of this isolate is not known. Substituting the MW965.26 V1/V2 domain into a neutralization-sensitive SF162 Env clone resulted in high resistance to standard anti-V3 monoclonal antibodies, demonstrating that this region possesses strong masking activity in a standard Env backbone and indicating that determinants elsewhere in MW965.26 Env are responsible for its unusual neutralization sensitivity. Key determinants for this phenotype were mapped by generating chimeric Envs between MW965.26 Env and a typical resistant Env clone, the consensus C (ConC) clone, and localized to two residues, Cys384 in the C3 domain and Asn502 in the C5 domain. Substituting the sensitizing mutations Y384C and K502N at these positions into several resistant primary Envs resulted in conversion to neutralization-sensitive phenotypes, demonstrating the generalizability of this effect. In contrast to the sensitizing effects of these substitutions on normally masked epitopes, these mutations reduced the sensitivity of VRC01-like epitopes overlapping the CD4-binding domain, while they had no effect on several other classes of broadly neutralizing epitopes, including members of several lineages of V2-dependent quaternary epitopes and representatives of N332 glycan-dependent epitopes (PGT121) and quaternary, cleavage-dependent epitopes centered at the gp41-gp120 interface on intact HIV-1 Env trimers (PGT151). These results identify novel substitutions in gp120 that regulate the expression of alternative conformations of Env and differentially affect the exposure of different classes of epitopes, thereby influencing the neutralization phenotype of primary HIV-1 isolates.IMPORTANCE A better understanding of the mechanisms that determine the wide range of neutralization sensitivity of circulating primary HIV-1 isolates would provide important information about the natural structural and conformational diversity of HIV-1 Env and how this affects the neutralization phenotype. A useful way of studying this is to determine the molecular basis for the unusually high neutralization sensitivities of the limited number of available tier 1a viruses. This study localized the neutralization sensitivity of MW965.26, an extremely sensitive subtype C-derived primary isolate, to two rare substitutions in the C3 and C5 domains and demonstrated that the sequences at these positions differentially affect the presentation of epitopes recognized by different classes of standard and conformation-dependent broadly neutralizing antibodies. These results provide novel insight into how these regions regulate the neutralization phenotype and provide tools for controlling the Env conformation that could have applications both for structural studies and in vaccine design.
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S. Coulibaly F, N. Thomas D, C. Youan BB. Anti-HIV lectins and current delivery strategies. AIMS MOLECULAR SCIENCE 2018. [DOI: 10.3934/molsci.2018.1.96] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
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10
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Snapp EL, McCaul N, Quandte M, Cabartova Z, Bontjer I, Källgren C, Nilsson I, Land A, von Heijne G, Sanders RW, Braakman I. Structure and topology around the cleavage site regulate post-translational cleavage of the HIV-1 gp160 signal peptide. eLife 2017; 6:26067. [PMID: 28753126 PMCID: PMC5577925 DOI: 10.7554/elife.26067] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Accepted: 07/26/2017] [Indexed: 12/29/2022] Open
Abstract
Like all other secretory proteins, the HIV-1 envelope glycoprotein gp160 is targeted to the endoplasmic reticulum (ER) by its signal peptide during synthesis. Proper gp160 folding in the ER requires core glycosylation, disulfide-bond formation and proline isomerization. Signal-peptide cleavage occurs only late after gp160 chain termination and is dependent on folding of the soluble subunit gp120 to a near-native conformation. We here detail the mechanism by which co-translational signal-peptide cleavage is prevented. Conserved residues from the signal peptide and residues downstream of the canonical cleavage site form an extended alpha-helix in the ER membrane, which covers the cleavage site, thus preventing cleavage. A point mutation in the signal peptide breaks the alpha helix allowing co-translational cleavage. We demonstrate that postponed cleavage of gp160 enhances functional folding of the molecule. The change to early cleavage results in decreased viral fitness compared to wild-type HIV.
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Affiliation(s)
- Erik Lee Snapp
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States
| | - Nicholas McCaul
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, Netherlands
| | - Matthias Quandte
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, Netherlands
| | - Zuzana Cabartova
- National Institute of Public Health, National Reference Laboratory for Viral Hepatitis, Prague, Czech Republic
| | - Ilja Bontjer
- Department of Medical Microbiology, Laboratory of Experimental Virology, Center for Infection and Immunity Amsterdam, Academic Medical Center, Amsterdam, Netherlands
| | - Carolina Källgren
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.,Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - IngMarie Nilsson
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.,Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Aafke Land
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, Netherlands
| | - Gunnar von Heijne
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.,Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Rogier W Sanders
- Department of Medical Microbiology, Laboratory of Experimental Virology, Center for Infection and Immunity Amsterdam, Academic Medical Center, Amsterdam, Netherlands
| | - Ineke Braakman
- Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Faculty of Science, Utrecht University, Utrecht, Netherlands
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11
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Henzy JE, Gifford RJ, Kenaley CP, Johnson WE. An Intact Retroviral Gene Conserved in Spiny-Rayed Fishes for over 100 My. Mol Biol Evol 2017; 34:634-639. [PMID: 28039384 PMCID: PMC5939848 DOI: 10.1093/molbev/msw262] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We have identified a retroviral envelope gene with a complete, intact open reading frame (ORF) in 20 species of spiny-rayed fishes (Acanthomorpha). The taxonomic distribution of the gene, "percomORF", indicates insertion into the ancestral lineage >110 Ma, making it the oldest known conserved gene of viral origin in a vertebrate genome. Underscoring its ancient provenence, percomORF exists as an isolated ORF within the intron of a widely conserved host gene, with no discernible proviral sequence nearby. Despite its remarkable age, percomORF retains canonical features of a retroviral glycoprotein, and tests for selection strongly suggest cooption for a host function. Retroviral envelope genes have been coopted for a role in placentogenesis by numerous lineages of mammals, including eutherians and marsupials, representing a variety of placental structures. Therefore percomORF's presence within the group Percomorpha-unique among spiny-finned fishes in having evolved placentation and live birth-is especially intriguing.
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Affiliation(s)
| | - Robert J. Gifford
- MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
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12
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Haddox HK, Dingens AS, Bloom JD. Experimental Estimation of the Effects of All Amino-Acid Mutations to HIV's Envelope Protein on Viral Replication in Cell Culture. PLoS Pathog 2016; 12:e1006114. [PMID: 27959955 PMCID: PMC5189966 DOI: 10.1371/journal.ppat.1006114] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 12/27/2016] [Accepted: 12/07/2016] [Indexed: 11/18/2022] Open
Abstract
HIV is notorious for its capacity to evade immunity and anti-viral drugs through rapid sequence evolution. Knowledge of the functional effects of mutations to HIV is critical for understanding this evolution. HIV's most rapidly evolving protein is its envelope (Env). Here we use deep mutational scanning to experimentally estimate the effects of all amino-acid mutations to Env on viral replication in cell culture. Most mutations are under purifying selection in our experiments, although a few sites experience strong selection for mutations that enhance HIV's replication in cell culture. We compare our experimental measurements of each site's preference for each amino acid to the actual frequencies of these amino acids in naturally occurring HIV sequences. Our measured amino-acid preferences correlate with amino-acid frequencies in natural sequences for most sites. However, our measured preferences are less concordant with natural amino-acid frequencies at surface-exposed sites that are subject to pressures absent from our experiments such as antibody selection. Our data enable us to quantify the inherent mutational tolerance of each site in Env. We show that the epitopes of broadly neutralizing antibodies have a significantly reduced inherent capacity to tolerate mutations, rigorously validating a pervasive idea in the field. Overall, our results help disentangle the role of inherent functional constraints and external selection pressures in shaping Env's evolution.
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Affiliation(s)
- Hugh K. Haddox
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
- Molecular and Cellular Biology PhD Program, University of Washington, Seattle, Washington, United States of America
| | - Adam S. Dingens
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
- Molecular and Cellular Biology PhD Program, University of Washington, Seattle, Washington, United States of America
| | - Jesse D. Bloom
- Basic Sciences Division and Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
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13
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HIV-1 Escape from a Peptidic Anchor Inhibitor through Stabilization of the Envelope Glycoprotein Spike. J Virol 2016; 90:10587-10599. [PMID: 27654295 DOI: 10.1128/jvi.01616-16] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 08/31/2016] [Indexed: 12/17/2022] Open
Abstract
The trimeric HIV-1 envelope glycoprotein spike (Env) mediates viral entry into cells by using a spring-loaded mechanism that allows for the controlled insertion of the Env fusion peptide into the target membrane, followed by membrane fusion. Env is the focus of vaccine research aimed at inducing protective immunity by antibodies as well as efforts to develop drugs that inhibit the viral entry process. The molecular factors contributing to Env stability and decay need to be understood better in order to optimally design vaccines and therapeutics. We generated viruses with resistance to VIR165, a peptidic inhibitor that binds the fusion peptide of the gp41 subunit and prevents its insertion into the target membrane. Interestingly, a number of escape viruses acquired substitutions in the C1 domain of the gp120 subunit (A60E, E64K, and H66R) that rendered these viruses dependent on the inhibitor. These viruses could infect target cells only when VIR165 was present after CD4 binding. Furthermore, the VIR165-dependent viruses were resistant to soluble CD4-induced Env destabilization and decay. These data suggest that VIR165-dependent Env proteins are kinetically trapped in the unliganded state and require the drug to negotiate CD4-induced conformational changes. These studies provide mechanistic insight into the action of the gp41 fusion peptide and its inhibitors and provide new ways to stabilize Env trimer vaccines. IMPORTANCE Because of the rapid development of HIV-1 drug resistance, new drug targets need to be explored continuously. The fusion peptide of the envelope glycoprotein can be targeted by anchor inhibitors. Here we describe virus escape from the anchor inhibitor VIR165. Interestingly, some escape viruses became dependent on the inhibitor for cell entry. We show that the identified escape mutations stabilize the ground state of the envelope glycoprotein and should thus be useful in the design of stabilized envelope-based HIV vaccines.
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14
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van den Kerkhof TLGM, de Taeye SW, Boeser-Nunnink BD, Burton DR, Kootstra NA, Schuitemaker H, Sanders RW, van Gils MJ. HIV-1 escapes from N332-directed antibody neutralization in an elite neutralizer by envelope glycoprotein elongation and introduction of unusual disulfide bonds. Retrovirology 2016; 13:48. [PMID: 27388013 PMCID: PMC4936165 DOI: 10.1186/s12977-016-0279-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 06/21/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Current HIV-1 immunogens are unable to induce antibodies that can neutralize a broad range of HIV-1 (broadly neutralizing antibodies; bNAbs). However, such antibodies are elicited in 10-30 % of HIV-1 infected individuals, and the co-evolution of the virus and the humoral immune responses in these individuals has attracted attention, because they can provide clues for vaccine design. RESULTS Here we characterized the NAb responses and envelope glycoprotein evolution in an HIV-1 infected "elite neutralizer" of the Amsterdam Cohort Studies on HIV-1 infection and AIDS who developed an unusually potent bNAb response rapidly after infection. The NAb response was dependent on the N332-glycan and viral resistance against the N332-glycan dependent bNAb PGT135 developed over time but viral escape did not occur at or near this glycan. In contrast, the virus likely escaped by increasing V1 length, with up to 21 amino acids, accompanied by the introduction of 1-3 additional glycans, as well as 2-4 additional cysteine residues within V1. CONCLUSIONS In the individual studied here, HIV-1 escaped from N332-glycan directed NAb responses without changing the epitope itself, but by elongating a variable loop that shields this epitope.
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Affiliation(s)
- Tom L G M van den Kerkhof
- Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands.,Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands
| | - Steven W de Taeye
- Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands
| | - Brigitte D Boeser-Nunnink
- Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands
| | - Dennis R Burton
- Department of Immunology and Microbial Science and IAVI Neutralizing Antibody Center, The Scripps Research Institute, La Jolla, CA, 92037, USA.,Ragon Institute of MGH, MIT, and Harvard, Cambridge, MA, 02139, USA
| | - Neeltje A Kootstra
- Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands
| | - Hanneke Schuitemaker
- Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands.,Janssen Pharmaceuticals, 2333 CN, Leiden, The Netherlands
| | - Rogier W Sanders
- Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands. .,Department of Microbiology and Immunology, Weill Medical College, Cornell University, New York, NY, 10065, USA.
| | - Marit J van Gils
- Department of Microbiology and Immunology, Weill Medical College, Cornell University, New York, NY, 10065, USA.
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15
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Ellgaard L, McCaul N, Chatsisvili A, Braakman I. Co- and Post-Translational Protein Folding in the ER. Traffic 2016; 17:615-38. [PMID: 26947578 DOI: 10.1111/tra.12392] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2015] [Revised: 02/26/2016] [Accepted: 03/03/2016] [Indexed: 12/19/2022]
Abstract
The biophysical rules that govern folding of small, single-domain proteins in dilute solutions are now quite well understood. The mechanisms underlying co-translational folding of multidomain and membrane-spanning proteins in complex cellular environments are often less clear. The endoplasmic reticulum (ER) produces a plethora of membrane and secretory proteins, which must fold and assemble correctly before ER exit - if these processes fail, misfolded species accumulate in the ER or are degraded. The ER differs from other cellular organelles in terms of the physicochemical environment and the variety of ER-specific protein modifications. Here, we review chaperone-assisted co- and post-translational folding and assembly in the ER and underline the influence of protein modifications on these processes. We emphasize how method development has helped advance the field by allowing researchers to monitor the progression of folding as it occurs inside living cells, while at the same time probing the intricate relationship between protein modifications during folding.
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Affiliation(s)
- Lars Ellgaard
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Nicholas McCaul
- Cellular Protein Chemistry, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Anna Chatsisvili
- Cellular Protein Chemistry, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Ineke Braakman
- Cellular Protein Chemistry, Faculty of Science, Utrecht University, Utrecht, The Netherlands
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16
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Reiser K, Mathys L, Curbo S, Pannecouque C, Noppen S, Liekens S, Engman L, Lundberg M, Balzarini J, Karlsson A. The Cellular Thioredoxin-1/Thioredoxin Reductase-1 Driven Oxidoreduction Represents a Chemotherapeutic Target for HIV-1 Entry Inhibition. PLoS One 2016; 11:e0147773. [PMID: 26816344 PMCID: PMC4729491 DOI: 10.1371/journal.pone.0147773] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Accepted: 01/07/2016] [Indexed: 11/30/2022] Open
Abstract
Background The entry of HIV into its host cell is an interesting target for chemotherapeutic intervention in the life-cycle of the virus. During entry, reduction of disulfide bridges in the viral envelope glycoprotein gp120 by cellular oxidoreductases is crucial. The cellular thioredoxin reductase-1 plays an important role in this oxidoreduction process by recycling electrons to thioredoxin-1. Therefore, thioredoxin reductase-1 inhibitors may inhibit gp120 reduction during HIV-1 entry. In this present study, tellurium-based thioredoxin reductase-1 inhibitors were investigated as potential inhibitors of HIV entry. Results The organotellurium compounds inhibited HIV-1 and HIV-2 replication in cell culture at low micromolar concentrations by targeting an early event in the viral infection cycle. Time-of-drug-addition studies pointed to virus entry as the drug target, more specifically: the organotellurium compound TE-2 showed a profile similar or close to that of the fusion inhibitor enfuvirtide (T-20). Surface plasmon resonance-based interaction studies revealed that the compounds do not directly interact with the HIV envelope glycoproteins gp120 and gp41, nor with soluble CD4, but instead, dose-dependently bind to thioredoxin reductase-1. By inhibiting the thioredoxin-1/thioredoxin reductase-1-directed oxidoreduction of gp120, the organotellurium compounds prevent conformational changes in the viral glycoprotein which are necessary during viral entry. Conclusion Our findings revealed that thioredoxin-1/thioredoxin reductase-1 acts as a cellular target for the inhibition of HIV entry.
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Affiliation(s)
- Kathrin Reiser
- Karolinska Institute, Department of Laboratory Medicine, Division of Clinical Microbiology, F68, Huddinge, Sweden
- * E-mail:
| | - Leen Mathys
- KU Leuven, Rega Institute for Medical Research, Minderbroederstraat 10, Leuven, Belgium
| | - Sophie Curbo
- Karolinska Institute, Department of Laboratory Medicine, Division of Clinical Microbiology, F68, Huddinge, Sweden
| | | | - Sam Noppen
- KU Leuven, Rega Institute for Medical Research, Minderbroederstraat 10, Leuven, Belgium
| | - Sandra Liekens
- KU Leuven, Rega Institute for Medical Research, Minderbroederstraat 10, Leuven, Belgium
| | - Lars Engman
- Uppsala University, Department of Chemistry–BMC, BOX 576, Uppsala, Sweden
| | - Mathias Lundberg
- Karolinska Institute, Department of Laboratory Medicine, Division of Clinical Microbiology, F68, Huddinge, Sweden
| | - Jan Balzarini
- KU Leuven, Rega Institute for Medical Research, Minderbroederstraat 10, Leuven, Belgium
| | - Anna Karlsson
- Karolinska Institute, Department of Laboratory Medicine, Division of Clinical Microbiology, F68, Huddinge, Sweden
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17
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Bailey LD, Kalyana Sundaram RV, Li H, Duffy C, Aneja R, Rosemary Bastian A, Holmes AP, Kamanna K, Rashad AA, Chaiken I. Disulfide Sensitivity in the Env Protein Underlies Lytic Inactivation of HIV-1 by Peptide Triazole Thiols. ACS Chem Biol 2015; 10:2861-73. [PMID: 26458166 DOI: 10.1021/acschembio.5b00381] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We investigated the mode of action underlying lytic inactivation of HIV-1 virions by peptide triazole thiol (PTT), in particular the relationship between gp120 disulfides and the C-terminal cysteine-SH required for virolysis. Obligate PTT dimer obtained by PTT SH cross-linking and PTTs with serially truncated linkers between pharmacophore isoleucine-ferrocenyltriazole-proline-tryptophan and cysteine-SH were synthesized. PTT variants showed loss of lytic activity but not binding and infection inhibition upon SH blockade. A disproportionate loss of lysis activity vs binding and infection inhibition was observed upon linker truncation. Molecular docking of PTT onto gp120 argued that, with sufficient linker length, the peptide SH could approach and disrupt several alternative gp120 disulfides. Inhibition of lysis by gp120 mAb 2G12, which binds at the base of the V3 loop, as well as disulfide mutational effects, argued that PTT-induced disruption of the gp120 disulfide cluster at the base of the V3 loop is an important step in lytic inactivation of HIV-1. Further, PTT-induced lysis was enhanced after treating virus with reducing agents dithiothreitol and tris (2-carboxyethyl)phosphine. Overall, the results are consistent with the view that the binding of PTT positions the peptide SH group to interfere with conserved disulfides clustered proximal to the CD4 binding site in gp120, leading to disulfide exchange in gp120 and possibly gp41, rearrangement of the Env spike, and ultimately disruption of the viral membrane. The dependence of lysis activity on thiol-disulfide interaction may be related to intrinsic disulfide exchange susceptibility in gp120 that has been reported previously to play a role in HIV-1 cell infection.
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Affiliation(s)
- Lauren D. Bailey
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Ramalingam Venkat Kalyana Sundaram
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
- School
of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania 19104, United States
| | - Huiyuan Li
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Caitlin Duffy
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Rachna Aneja
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | | | - Andrew P. Holmes
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Kantharaju Kamanna
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Adel A. Rashad
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Irwin Chaiken
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
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18
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Mathys L, Balzarini J. Several N-Glycans on the HIV Envelope Glycoprotein gp120 Preferentially Locate Near Disulphide Bridges and Are Required for Efficient Infectivity and Virus Transmission. PLoS One 2015; 10:e0130621. [PMID: 26121645 PMCID: PMC4488071 DOI: 10.1371/journal.pone.0130621] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 05/21/2015] [Indexed: 12/24/2022] Open
Abstract
The HIV envelope glycoprotein gp120 contains nine disulphide bridges and is highly glycosylated, carrying on average 24 N-linked glycans. Using a probability calculation, we here demonstrate that there is a co-localization of disulphide bridges and N-linked glycans in HIV-1 gp120, with a predominance of N-linked glycans in close proximity to disulphide bridges, at the C-terminal side of the involved cysteines. Also, N-glycans are frequently found immediately adjacent to disulphide bridges in gp120 at the N-terminal side of the involved cysteines. In contrast, N-glycans at positions close to, but not immediately neighboring disulphide bridges seem to be disfavored at the N-terminal side of the involved cysteines. Such a pronounced co-localization of disulphide bridges and N-glycans was also found for the N-glycans on glycoprotein E1 of the hepatitis C virus (HCV) but not for other heavily glycosylated proteins such as E2 from HCV and the surface GP from Ebola virus. The potential functional role of the presence of N-glycans near disulphide bridges in HIV-1 gp120 was studied using site-directed mutagenesis, either by deleting conserved N-glycans or by inserting new N-glycosylation sites near disulphide bridges. The generated HIV-1NL4.3 mutants were subjected to an array of assays, determining the envelope glycoprotein levels in mutant viral particles, their infectivity and the capture and transmission efficiencies of mutant virus particles by DC-SIGN. Three N-glycans located nearby disulphide bridges were found to be crucial for the preservation of several of these functions of gp120. In addition, introduction of new N-glycans upstream of several disulphide bridges, at locations where there was a significant absence of N-glycans in a broad variety of virus strains, was found to result in a complete loss of viral infectivity. It was shown that the N-glycan environment around well-defined disulphide bridges of gp120 is highly critical to allow efficient viral infection and transmission.
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Affiliation(s)
- Leen Mathys
- Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
| | - Jan Balzarini
- Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
- * E-mail:
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19
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Nguyen HNP, Steede NK, Robinson JE, Landry SJ. Conformational instability governed by disulfide bonds partitions the dominant from subdominant helper T-cell responses specific for HIV-1 envelope glycoprotein gp120. Vaccine 2015; 33:2887-96. [PMID: 25944298 DOI: 10.1016/j.vaccine.2015.04.082] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 03/30/2015] [Accepted: 04/22/2015] [Indexed: 01/07/2023]
Abstract
Most individuals infected with human immunodeficiency virus type 1 (HIV-1) generate a CD4(+) T-cell response that is dominated by a few epitopes. Immunodominance may be counterproductive because a broad CD4(+) T-cell response is associated with reduced viral load. Previous studies indicated that antigen three-dimensional structure controls antigen processing and presentation and therefore CD4(+) T-cell epitope dominance. Dominant epitopes occur adjacent to the V1-V2, V3, and V4 loops because proteolytic antigen processing in the loops promotes presentation of adjacent sequences. In this study, three gp120 (strain JR-FL) variants were constructed, in which deletions of single outer-domain disulfide bonds were expected to introduce local conformational flexibility and promote presentation of additional CD4(+) T-cell epitopes. Following mucosal immunization of C57BL/6 mice with wild-type or variant gp120 lacking the V3-flanking disulfide bond, the typical pattern of dominant epitopes was observed, suggesting that the disulfide bond posed no barrier to antigen presentation. In mice that lacked gamma interferon-inducible lysosomal thioreductase (GILT), proliferative responses to the typically dominant epitopes of gp120 were selectively depressed, and the dominance pattern was rearranged. Deletion of the V3-flanking disulfide bond or one of the V4-flanking disulfide bonds partially restored highly proliferative responses to the typically dominant epitopes. These results reveal an acute dependence of dominant CD4(+) T-cell responses on the native gp120 conformation.
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Affiliation(s)
- Hong-Nam P Nguyen
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112, USA
| | - N Kalaya Steede
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112, USA
| | - James E Robinson
- Department of Pediatrics, Tulane University School of Medicine, New Orleans, LA, USA
| | - Samuel J Landry
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112, USA.
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20
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Haworth NL, Wouters MA. Cross-strand disulfides in the non-hydrogen bonding site of antiparallel β-sheet (aCSDns): poised for biological switching. RSC Adv 2015. [DOI: 10.1039/c5ra10672a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
aCSDns are forbidden disulfides with protein redox-activity. Within the aCSDn structural motif, a cognate substrate of Trx-like enzymes, the disulfide bonds are strained and metastable, facilitating their role as redox-regulated protein switches.
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Affiliation(s)
- Naomi L. Haworth
- Life and Environmental Sciences
- Deakin University
- Geelong 3217
- Australia
- Victor Chang Cardiac Research Institute
| | - Merridee A. Wouters
- Olivia Newton-John Cancer Research Institute
- Heidelberg 3084
- Australia
- School of Cancer Medicine
- La Trobe University
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21
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Costantini LM, Irvin SC, Kennedy SC, Guo F, Goldstein H, Herold BC, Snapp EL. Engineering and exploitation of a fluorescent HIV-1 gp120 for live cell CD4 binding assays. Virology 2014; 476:240-248. [PMID: 25555152 DOI: 10.1016/j.virol.2014.12.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Revised: 10/08/2014] [Accepted: 12/09/2014] [Indexed: 10/24/2022]
Abstract
The HIV-1 envelope glycoprotein, gp120, binds the host cell receptor, CD4, in the initial step of HIV viral entry and infection. This process is an appealing target for the development of inhibitory drugs and neutralizing antibodies. To study gp120 binding and intracellular trafficking, we engineered a fluorescent fusion of the humanized gp120 JRFL HIV-1 variant and GFP. Gp120-sfGFP is glycosylated with human sugars, robustly expressed, and secreted from cultured human cells. Protein dynamics, quality control, and trafficking can be visualized in live cells. The fusion protein can be readily modified with different gp120 variants or fluorescent proteins. Finally, secreted gp120-sfGFP enables a sensitive and easy binding assay that can quantitatively screen potential inhibitors of gp120-CD4 binding on live cells via fluorescence imaging or laser scanning cytometry. This adaptable research tool should aid in studies of gp120 cell biology and the development of novel anti-HIV drugs.
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Affiliation(s)
- Lindsey M Costantini
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
| | - Susan C Irvin
- Department of Pediatrics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA; Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
| | - Steven C Kennedy
- Department of Pediatrics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
| | - Feng Guo
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
| | - Harris Goldstein
- Department of Pediatrics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA; Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
| | - Betsy C Herold
- Department of Pediatrics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA; Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
| | - Erik L Snapp
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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22
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Mathys L, Balzarini J. The role of N-glycans of HIV-1 gp41 in virus infectivity and susceptibility to the suppressive effects of carbohydrate-binding agents. Retrovirology 2014; 11:107. [PMID: 25499264 PMCID: PMC4269863 DOI: 10.1186/s12977-014-0107-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Accepted: 11/11/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Carbohydrate-binding agents (CBAs) are potent antiretroviral compounds that target the N-glycans on the HIV-1 envelope glycoproteins. The development of phenotypic resistance to CBAs by the virus is accompanied by the deletion of multiple N-linked glycans of the surface envelope glycoprotein gp120. Recently, also an N-glycan on the transmembrane envelope glycoprotein gp41 was shown to be deleted during CBA resistance development. RESULTS We generated HIV-1 mutants lacking gp41 N-glycans and determined the influence of these glycan deletions on the viral phenotype (infectivity, CD4 binding, envelope glycoprotein incorporation in the viral particle and on the transfected cell, virus capture by DC-SIGN(+) cells and transmission of DC-SIGN-captured virions to CD4(+) T-lymphocytes) and on the phenotypic susceptibility of HIV-1 to a selection of CBAs. It was shown that some gp41 N-glycans are crucial for the infectivity of the virus. In particular, lack of an intact N616 glycosylation site was shown to result in the loss of viral infectivity of several (i.e. the X4-tropic IIIB and NL4.3 strains, and the X4/R5-tropic HE strain), but not all (i.e. the R5-tropic ADA strain) studied HIV-1 strains. In accordance, we found that the gp120 levels in the envelope of N616Q mutant gp41 strains NL4.3, IIIB and HE were severely decreased. In contrast, N616Q gp41 mutant HIV-1ADA contained gp120 levels similar to the gp120 levels in WT HIV-1ADA virus. Concomitantly deleting multiple gp41 N-glycans was often highly detrimental for viral infectivity. Using surface plasmon resonance technology we showed that CBAs have a pronounced affinity for both gp120 and gp41. However, the antiviral activity of CBAs is not dependent on the concomitant presence of all gp41 glycans. Single gp41 glycan deletions had no marked effects on CBA susceptibility, whereas some combinations of two to three gp41 glycan-deletions had a minor effect on CBA activity. CONCLUSIONS We revealed the importance of some gp41 N-linked glycans, in particular the N616 glycan which was shown to be absolutely indispensable for the infectivity potential of several virus strains. In addition, we demonstrated that the deletion of up to three gp41 N-linked glycans only slightly affected CBA susceptibility.
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Affiliation(s)
- Leen Mathys
- Rega Institute for Medical Research, KU Leuven, Minderbroedersstraat 10, B-3000, Leuven, Belgium.
| | - Jan Balzarini
- Rega Institute for Medical Research, KU Leuven, Minderbroedersstraat 10, B-3000, Leuven, Belgium.
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Comprehensive analysis of contributions from protein conformational stability and major histocompatibility complex class II-peptide binding affinity to CD4+ epitope immunogenicity in HIV-1 envelope glycoprotein. J Virol 2014; 88:9605-15. [PMID: 24920818 DOI: 10.1128/jvi.00789-14] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
UNLABELLED Helper T-cell epitope dominance in human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 is not adequately explained by peptide binding to major histocompatibility complex (MHC) proteins. Antigen processing potentially influences epitope dominance, but few, if any, studies have attempted to reconcile the influences of antigen processing and MHC protein binding for all helper T-cell epitopes of an antigen. Epitopes of gp120 identified in both humans and mice occur on the C-terminal flanks of flexible segments that are likely to be proteolytic cleavage sites. In this study, the influence of gp120 conformation on the dominance pattern in gp120 from HIV strain 89.6 was examined in CBA mice, whose MHC class II protein has one of the most well defined peptide-binding preferences. Only one of six dominant epitopes contained the most conserved element of the I-Ak binding motif, an aspartic acid. Destabilization of the gp120 conformation by deletion of single disulfide bonds preferentially enhanced responses to the cryptic I-Ak motif-containing sequences, as reported by T-cell proliferation or cytokine secretion. Conversely, inclusion of CpG in the adjuvant with gp120 enhanced responses to the dominant CD4+ T-cell epitopes. The gp120 destabilization affected secretion of some cytokines more than others, suggesting that antigen conformation could modulate T-cell functions through mechanisms of antigen processing. IMPORTANCE CD4+ helper T cells play an essential role in protection against HIV and other pathogens. Thus, the sites of helper T-cell recognition, the dominant epitopes, are targets for vaccine design; and the corresponding T cells may provide markers for monitoring infection and immunity. However, T-cell epitopes are difficult to identify and predict. It is also unclear whether CD4+ T cells specific for one epitope are more protective than T cells specific for other epitopes. This work shows that the three-dimensional (3D) structure of an HIV protein partially determines which epitopes are dominant, most likely by controlling the breakdown of HIV into peptides. Moreover, some types of signals from CD4+ T cells are affected by the HIV protein 3D structure; and thus the protectiveness of a particular peptide vaccine could be related to its location in the 3D structure.
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Isik G, van Montfort T, Boot M, Cobos Jiménez V, Kootstra NA, Sanders RW. Chimeric HIV-1 envelope glycoproteins with potent intrinsic granulocyte-macrophage colony-stimulating factor (GM-CSF) activity. PLoS One 2013; 8:e60126. [PMID: 23565193 PMCID: PMC3615126 DOI: 10.1371/journal.pone.0060126] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Accepted: 02/21/2013] [Indexed: 11/18/2022] Open
Abstract
HIV-1 acquisition can be prevented by broadly neutralizing antibodies (BrNAbs) that target the envelope glycoprotein complex (Env). An ideal vaccine should therefore be able to induce BrNAbs that can provide immunity over a prolonged period of time, but the low intrinsic immunogenicity of HIV-1 Env makes the elicitation of such BrNAbs challenging. Co-stimulatory molecules can increase the immunogenicity of Env and we have engineered a soluble chimeric Env trimer with an embedded granulocyte-macrophage colony-stimulating factor (GM-CSF) domain. This chimeric molecule induced enhanced B and helper T cell responses in mice compared to Env without GM-CSF. We studied whether we could optimize the activity of the embedded GM-CSF as well as the antigenic structure of the Env component of the chimeric molecule. We assessed the effect of truncating GM-CSF, removing glycosylation-sites in GM-CSF, and adjusting the linker length between GM-CSF and Env. One of our designed Env(GM-CSF) chimeras improved GM-CSF-dependent cell proliferation by 6-fold, reaching the same activity as soluble recombinant GM-CSF. In addition, we incorporated GM-CSF into a cleavable Env trimer and found that insertion of GM-CSF did not compromise Env cleavage, while Env cleavage did not compromise GM-CSF activity. Importantly, these optimized Env(GM-CSF) proteins were able to differentiate human monocytes into cells with a macrophage-like phenotype. Chimeric Env(GM-CSF) should be useful for improving humoral immunity against HIV-1 and these studies should inform the design of other chimeric proteins.
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Affiliation(s)
- Gözde Isik
- Department of Medical Microbiology, Laboratory of Experimental Virology, Center for Infection and Immunity Amsterdam, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Thijs van Montfort
- Department of Medical Microbiology, Laboratory of Experimental Virology, Center for Infection and Immunity Amsterdam, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Maikel Boot
- Department of Medical Microbiology, Laboratory of Experimental Virology, Center for Infection and Immunity Amsterdam, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Viviana Cobos Jiménez
- Department of Experimental Immunology, Sanquin Research, Landsteiner Laboratory, Center for Infection and Immunity Amsterdam, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Neeltje A. Kootstra
- Department of Experimental Immunology, Sanquin Research, Landsteiner Laboratory, Center for Infection and Immunity Amsterdam, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Rogier W. Sanders
- Department of Medical Microbiology, Laboratory of Experimental Virology, Center for Infection and Immunity Amsterdam, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, United States of America
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Wahid A, Helle F, Descamps V, Duverlie G, Penin F, Dubuisson J. Disulfide bonds in hepatitis C virus glycoprotein E1 control the assembly and entry functions of E2 glycoprotein. J Virol 2013; 87:1605-17. [PMID: 23175356 PMCID: PMC3554189 DOI: 10.1128/jvi.02659-12] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Accepted: 11/09/2012] [Indexed: 12/24/2022] Open
Abstract
Class II membrane fusion proteins have been described in viruses in which the envelope proteins are derived from a precursor polyprotein containing two transmembrane glycoproteins arranged in tandem. Although the second protein, which carries the membrane fusion function, is in general well characterized, the companion protein, which is a protein chaperone for the folding of the fusion protein, is less well characterized for some viruses, like hepatitis C virus (HCV). To investigate the role of the class II companion glycoprotein E1 of HCV, we chose to target conserved cysteine residues in the protein, and we systematically mutated them in a full-length infectious HCV clone by reverse genetics. All the mutants were infectious, albeit with lower titers than the wild-type virus. The reduced infectivity was in part due to a decrease in viral assembly, as revealed by measurement of intracellular infectivity and by quantification of core protein released from cells transfected with mutant genomes. Analyses of mutated proteins did not show any major defect in folding. However, the mutations reduced virus stability, and they could also affect the density of infectious viral particles. Mutant viruses also showed a defect in cell-to-cell transmission. Finally, our data indicate that HCV glycoprotein E1 can also affect the fusion protein E2 by modulating its recognition by the cellular coreceptor CD81. Therefore, in the context of HCV, our data identify an additional function of a class II companion protein as a molecule that can control the binding capacity of the fusion protein.
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Affiliation(s)
- Ahmed Wahid
- Center for Infection and Immunity of Lille (CIIL), INSERM U1019, CNRS UMR8204, Institut Pasteur de Lille, Université Lille Nord de France, Lille, France
- Department of Biochemistry, Faculty of Pharmacy, Minia, University, Minia, Egypt
| | - François Helle
- Laboratoire de Virologie EA4294, Centre Hospitalier Universitaire d'Amiens, Université de Picardie Jules Verne, Amiens, France
| | - Véronique Descamps
- Laboratoire de Virologie EA4294, Centre Hospitalier Universitaire d'Amiens, Université de Picardie Jules Verne, Amiens, France
| | - Gilles Duverlie
- Laboratoire de Virologie EA4294, Centre Hospitalier Universitaire d'Amiens, Université de Picardie Jules Verne, Amiens, France
| | - François Penin
- Institut de Biologie et Chimie des Protéines, Bases Moléculaires et Structurales des Systèmes Infectieux, UMR-5086-CNRS, Université de Lyon, Lyon, France
| | - Jean Dubuisson
- Center for Infection and Immunity of Lille (CIIL), INSERM U1019, CNRS UMR8204, Institut Pasteur de Lille, Université Lille Nord de France, Lille, France
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26
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Haworth NL, Wouters MA. Between-strand disulfides: forbidden disulfides linking adjacent β-strands. RSC Adv 2013. [DOI: 10.1039/c3ra42486c] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
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Stantchev TS, Paciga M, Lankford CR, Schwartzkopff F, Broder CC, Clouse KA. Cell-type specific requirements for thiol/disulfide exchange during HIV-1 entry and infection. Retrovirology 2012. [PMID: 23206338 PMCID: PMC3526565 DOI: 10.1186/1742-4690-9-97] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND The role of disulfide bond remodeling in HIV-1 infection is well described, but the process still remains incompletely characterized. At present, the data have been predominantly obtained using established cell lines and/or CXCR4-tropic laboratory-adapted virus strains. There is also ambiguity about which disulfide isomerases/reductases play a major role in HIV-1 entry, as protein disulfide isomerase (PDI) and/or thioredoxin (Trx) have emerged as the two enzymes most often implicated in this process. RESULTS We have extended our previous findings and those of others by focusing on CCR5-using HIV-1 strains and their natural targets--primary human macrophages and CD4+ T lymphocytes. We found that the nonspecific thiol/disulfide exchange inhibitor, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), significantly reduced HIV-1 entry and infection in cell lines, human monocyte-derived macrophages (MDM), and also phytohemagglutinin (PHA)-stimulated peripheral blood mononuclear cells (PBMC). Subsequent studies were performed using specific anti-PDI or Trx monoclonal antibodies (mAb) in HIV-1 envelope pseudotyped and wild type (wt) virus infection systems. Although human donor-to-donor variability was observed as expected, Trx appeared to play a greater role than PDI in HIV-1 infection of MDM. In contrast, PDI, but not Trx, was predominantly involved in HIV-1 entry and infection of the CD4+/CCR5+ T cell line, PM-1, and PHA-stimulated primary human T lymphocytes. Intriguingly, both PDI and Trx were present on the surface of MDM, PM-1 and PHA-stimulated CD4+ T cells. However, considerably lower levels of Trx were detected on freshly isolated CD4+ lymphocytes, compared to PHA-stimulated cells. CONCLUSIONS Our findings clearly demonstrate the role of thiol/disulfide exchange in HIV-1 entry in primary T lymphocytes and MDM. They also establish a cell-type specificity regarding the involvement of particular disulfide isomerases/reductases in this process and may provide an explanation for differences among previously published studies. More importantly, from an in vivo perspective, the preferential utilization of PDI may be relevant to the HIV-1 entry and establishment of virus reservoirs in resting CD4+ cells, while the elevated levels of Trx reported in the chronic stages of HIV-1 infection may facilitate the virus entry in macrophages and help to sustain high viremia during the decline of T lymphocytes.
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Affiliation(s)
- Tzanko S Stantchev
- Laboratory of Cell Biology, Division of Monoclonal Antibodies, U.S. Food and Drug Administration, Bethesda, MD 20892, USA
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Soleimani P, Barzegar A, Movafeghi A. Phylogenetic study of SIVcpz MT145 virus based on proteome and genome analysis. J Biomol Struct Dyn 2012; 30:328-37. [DOI: 10.1080/07391102.2012.680032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Transient transfection coupled to baculovirus infection for rapid protein expression screening in insect cells. J Struct Biol 2012; 179:46-55. [PMID: 22580066 DOI: 10.1016/j.jsb.2012.04.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Revised: 04/20/2012] [Accepted: 04/24/2012] [Indexed: 12/13/2022]
Abstract
Baculovirus infected insect cells are widely used for heterologous protein expression. Despite the power of this system, the use of baculovirus techniques for protein expression screening is hampered by the time and resources needed to generate each recombinant baculovirus. Here, we show that a transfection/infection based expression system is suitable for screening of expression constructs in insect cells and represents a valid alternative to other traditional screening methodologies using recombinant baculovirus. The described method is based on gene delivery by transfection coupled to the induction of protein expression by non-recombinant baculovirus infection. Vectors that control expression by a combination of the baculovirus promoters ie1 and p10 and the enhancer element hr5 are among the ones suitable for this method. Infection with non-recombinant baculovirus drastically increases the basal activity of these elements, leading to protein over-expression. Multiple vectors can be simultaneously co-transfected/infected, making transfection/infection amenable for screening of multiple co-expressed proteins and protein complexes. Taken together, our results prove that the transfection/infection protocol is a valid and innovative approach for increasing speed and reducing costs of protein expression screening for structural and functional studies.
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McCaffrey K, Boo I, Tewierek K, Edmunds ML, Poumbourios P, Drummer HE. Role of conserved cysteine residues in hepatitis C virus glycoprotein e2 folding and function. J Virol 2012; 86:3961-74. [PMID: 22278231 PMCID: PMC3302498 DOI: 10.1128/jvi.05396-11] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Accepted: 01/11/2012] [Indexed: 01/22/2023] Open
Abstract
Hepatitis C virus glycoprotein E2 contains 18 conserved cysteines predicted to form nine disulfide pairs. In this study, a comprehensive cysteine-alanine mutagenesis scan of all 18 cysteine residues was performed in E1E2-pseudotyped retroviruses (HCVpp) and recombinant E2 receptor-binding domain (E2 residues 384 to 661 [E2(661)]). All 18 cysteine residues were absolutely required for HCVpp entry competence. The phenotypes of individual cysteines and pairwise mutation of disulfides were largely the same for retrovirion-incorporated E2 and E2(661), suggesting their disulfide arrangements are similar. However, the contributions of each cysteine residue and the nine disulfides to E2 structure and function varied. Individual Cys-to-Ala mutations revealed discordant effects, where removal of one Cys within a pair had minimal effect on H53 recognition and CD81 binding (C486 and C569) while mutation of its partner abolished these functions (C494 and C564). Removal of disulfides at C581-C585 and C452-C459 significantly reduced the amount of E1 coprecipitated with E2, while all other disulfides were absolutely required for E1E2 heterodimerization. Remarkably, E2(661) tolerates the presence of four free cysteines, as simultaneous mutation of C452A, C486A, C569A, C581A, C585A, C597A, and C652A (M+C597A) retained wild-type CD81 binding. Thus, only one disulfide from each of the three predicted domains, C429-C552 (DI), C503-C508 (DII), and C607-C644 (DIII), is essential for the assembly of the E2(661) CD81-binding site. Furthermore, the yield of total monomeric E2 increased to 70% in M+C597A. These studies reveal the contribution of each cysteine residue and the nine disulfide pairs to E2 structure and function.
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Affiliation(s)
- Kathleen McCaffrey
- Burnet Institute, Melbourne, Australia
- Department of Microbiology and Immunology, University of Melbourne, Parkville, Australia
| | - Irene Boo
- Burnet Institute, Melbourne, Australia
| | | | | | - Pantelis Poumbourios
- Burnet Institute, Melbourne, Australia
- Department of Microbiology, Monash University, Clayton, Australia
| | - Heidi E. Drummer
- Burnet Institute, Melbourne, Australia
- Department of Microbiology and Immunology, University of Melbourne, Parkville, Australia
- Department of Microbiology, Monash University, Clayton, Australia
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31
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Thioredoxin-1 and protein disulfide isomerase catalyze the reduction of similar disulfides in HIV gp120. Int J Biochem Cell Biol 2012; 44:556-62. [PMID: 22230366 DOI: 10.1016/j.biocel.2011.12.015] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2011] [Revised: 12/13/2011] [Accepted: 12/22/2011] [Indexed: 12/29/2022]
Abstract
HIV-1 enters cells via interaction of the viral glycoprotein gp120, the host cell surface receptor CD4 and the co-receptors CCR5 or CXCR4. For entry, gp120 undergoes conformational changes that depend on the reduction of one or more disulfides. Previous studies indicate that protein disulfide isomerase (PDI), thioredoxin-1 (Trx1), and glutaredoxin-1 (Grx1) catalyze gp120 reduction, but their specific disulfide targets are not known. Here, it was demonstrated that PDI and Trx1 have similar gp120 disulfide targets as determined by labeling after reduction, but with some pattern differences, including overall stronger labeling with Trx1 than with PDI. Furthermore, uneven labeling of the residues of a disulfide may reflect altered accessibility by conformational changes upon the reduction process. Since both PDI and Trx1 may be involved in viral entry, compounds that target the host redox system or the viral gp120 were tested in vitro to investigate whether redox regulation is a target for anti-HIV therapy. Carbohydrate binding agents (CBAs), previously shown to bind gp120 and inhibit HIV entry, were now demonstrated to inhibit gp120 disulfide reduction. Auranofin, an inhibitor of thioredoxin reductase 1 (TrxR1), also showed inhibitory activity towards HIV infection, although close to its cytotoxic concentration. Our results demonstrate that both the host redox system and the viral surface glycoproteins are of interest for the development of new generations of anti-HIV therapeutics.
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Alternative coreceptor requirements for efficient CCR5- and CXCR4-mediated HIV-1 entry into macrophages. J Virol 2011; 85:10699-709. [PMID: 21835796 DOI: 10.1128/jvi.05510-11] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Macrophage tropism of human immunodeficiency virus type 1 (HIV-1) is distinct from coreceptor specificity of the viral envelope glycoproteins (Env), but the virus-cell interactions that contribute to efficient HIV-1 entry into macrophages, particularly via CXCR4, are not well understood. Here, we characterized a panel of HIV-1 Envs that use CCR5 (n = 14) or CXCR4 (n = 6) to enter monocyte-derived macrophages (MDM) with various degrees of efficiency. Our results show that efficient CCR5-mediated MDM entry by Env-pseudotyped reporter viruses is associated with increased tolerance of several mutations within the CCR5 N terminus. In contrast, efficient CXCR4-mediated MDM entry was associated with reduced tolerance of a large deletion within the CXCR4 N terminus. Env sequence analysis and structural modeling identified amino acid variants at positions 261 and 263 within the gp41-interactive region of gp120 and a variant at position 326 within the gp120 V3 loop that were associated with efficient CXCR4-mediated MDM entry. Mutagenesis studies showed that the gp41 interaction domain variants exert a significant but strain-specific influence on CXCR4-mediated MDM entry, suggesting that the structural integrity of the gp120-gp41 interface is important for efficient CXCR4-mediated MDM entry of certain HIV-1 strains. However, the presence of Ile326 in the gp120 V3 loop stem, which we show by molecular modeling is located at the gp120-coreceptor interface and predicted to interact with the CXCR4 N terminus, was found to be critical for efficient CXCR4-mediated MDM entry of divergent CXCR4-using Envs. Together, the results of our study provide novel insights into alternative mechanisms of Env-coreceptor engagement that are associated with efficient CCR5- and CXCR4-mediated HIV-1 entry into macrophages.
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Martin G, Burke B, Thaï R, Dey AK, Combes O, Ramos OHP, Heyd B, Geonnotti AR, Montefiori DC, Kan E, Lian Y, Sun Y, Abache T, Ulmer JB, Madaoui H, Guérois R, Barnett SW, Srivastava IK, Kessler P, Martin L. Stabilization of HIV-1 envelope in the CD4-bound conformation through specific cross-linking of a CD4 mimetic. J Biol Chem 2011; 286:21706-16. [PMID: 21487012 DOI: 10.1074/jbc.m111.232272] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CD4 binding on gp120 leads to the exposure of highly conserved regions recognized by the HIV co-receptor CCR5 and by CD4-induced (CD4i) antibodies. A covalent gp120-CD4 complex was shown to elicit CD4i antibody responses in monkeys, which was correlated with control of the HIV virus infection (DeVico, A., Fouts, T., Lewis, G. K., Gallo, R. C., Godfrey, K., Charurat, M., Harris, I., Galmin, L., and Pal, R. (2007) Proc. Natl. Acad. Sci. U.S.A. 104, 17477-17482). Because the inclusion of CD4 in a vaccine formulation should be avoided, due to potential autoimmune reactions, we engineered small sized CD4 mimetics (miniCD4s) that are poorly immunogenic and do not induce anti-CD4 antibodies. We made covalent complexes between such an engineered miniCD4 and gp120 or gp140, through a site-directed coupling reaction. These complexes were recognized by CD4i antibodies as well as by the HIV co-receptor CCR5. In addition, they elicit CD4i antibody responses in rabbits and therefore represent potential vaccine candidates that mimic an important HIV fusion intermediate, without autoimmune hazard.
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Affiliation(s)
- Grégoire Martin
- Commissariat à l'Energie Atomique, iBiTecS, Service d'Ingénierie Moléculaire des Protéines, Gif-sur-Yvette F-91191, France
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Adaptation of subtype a human immunodeficiency virus type 1 envelope to pig-tailed macaque cells. J Virol 2011; 85:4409-20. [PMID: 21325401 DOI: 10.1128/jvi.02244-10] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The relevance of simian/human immunodeficiency virus (SHIV) infection of macaques to HIV-1 infection in humans depends on how closely SHIVs mimic HIV-1 transmission, pathogenesis, and diversity. Circulating HIV-1 strains are predominantly subtypes C and A and overwhelmingly require CCR5 for entry, yet most SHIVs incorporate CXCR4-using subtype B envelopes (Envs). While pathogenic subtype C-based SHIVs have been constructed, the subtype A-based SHIVs (SHIV-As) constructed to date have been unable to replicate in macaque cells. To understand the barriers to SHIV-A replication in macaque cells, HIVA(Q23)/SIV(vif) was constructed by engineering a CCR5-tropic subtype A provirus to express SIV vif, which counters the macaque APOBEC3G restriction. HIVA(Q23)/SIV(vif) replicated poorly in pig-tailed macaque (Ptm) lymphocytes, but viruses were adapted to Ptm lymphocytes. Two independent mutations in gp120, G312V (V3 loop) and A204E (C2 region), were identified that increased peak virus levels by >100-fold. Introduction of G312V and A204E to multiple subtype A Envs and substitution of G312 and A204 with other residues increased entry into Ptm cells by 10- to 100-fold. G312V and A204E Env variants continued to require CCR5 for entry but were up to 50- and 200-fold more sensitive to neutralization by IgG1b12 and soluble CD4 and had a 5- to 50-fold increase in their ability to utilize Ptm CD4 compared to their wild-type counterparts. These findings identify the inefficient use of Ptm CD4 as an unappreciated restriction to subtype A HIV-1 replication in Ptm cells and reveal amino acid changes to gp120 that can overcome this barrier.
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Cerutti N, Mendelow BV, Napier GB, Papathanasopoulos MA, Killick M, Khati M, Stevens W, Capovilla A. Stabilization of HIV-1 gp120-CD4 receptor complex through targeted interchain disulfide exchange. J Biol Chem 2010; 285:25743-52. [PMID: 20538591 PMCID: PMC2919137 DOI: 10.1074/jbc.m110.144121] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 06/09/2010] [Indexed: 12/17/2022] Open
Abstract
HIV-1 enters cells via interaction between the trimeric envelope (Env) glycoprotein gp120/gp41 and the host cell surface receptor molecule CD4. The requirement of CD4 for viral entry has rationalized the development of recombinant CD4-based proteins as competitive viral attachment inhibitors and immunotherapeutic agents. In this study, we describe a novel recombinant CD4 protein designed to bind gp120 through a targeted disulfide-exchange mechanism. According to structural models of the gp120-CD4 receptor complex, substitution of Ser(60) on the CD4 domain 1 alpha-helix with Cys positions a thiol in proximity of the gp120 V1/V2 loop disulfide (Cys(126)-Cys(196)), satisfying the stereochemical and geometric conditions for redox exchange between CD4 Cys(60) and gp120 Cys(126), and the consequent formation of an interchain disulfide bond. In this study, we provide experimental evidence for this effect by describing the expression, purification, refolding, receptor binding and antiviral activity analysis of a recombinant two-domain CD4 variant containing the S60C mutation (2dCD4-S60C). We show that 2dCD4-S60C binds HIV-1 gp120 with a significantly higher affinity than wild-type protein under conditions that facilitate disulfide exchange and that this translates into a corresponding increase in the efficacy of CD4-mediated viral entry inhibition. We propose that targeted redox exchange between conserved gp120 disulfides and nucleophilic moieties positioned strategically on CD4 (or CD4-like scaffolds) conceptualizes a new strategy in the development of high affinity HIV-1 Env ligands, with important implications for therapy and vaccine development. More generally, this chalcogen substitution approach provides a general means of stabilizing receptor-ligand complexes where the structural and biophysical conditions for disulfide exchange are satisfied.
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Affiliation(s)
- Nichole Cerutti
- Elevation Biotech, 8 Blackwood Avenue, Parktown 2193, Johannesburg, and
| | - Barry V. Mendelow
- From the Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, Johannesburg
| | - Grant B. Napier
- Elevation Biotech, 8 Blackwood Avenue, Parktown 2193, Johannesburg, and
| | - Maria A. Papathanasopoulos
- From the Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, Johannesburg
- Elevation Biotech, 8 Blackwood Avenue, Parktown 2193, Johannesburg, and
| | - Mark Killick
- Elevation Biotech, 8 Blackwood Avenue, Parktown 2193, Johannesburg, and
| | - Makobetsa Khati
- the Council for Scientific and Industrial Research, P. O. Box 395, Pretoria 0001, South Africa
| | - Wendy Stevens
- From the Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, Johannesburg
| | - Alexio Capovilla
- From the Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, Johannesburg
- Elevation Biotech, 8 Blackwood Avenue, Parktown 2193, Johannesburg, and
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Baculovirus GP64 disulfide bonds: the intermolecular disulfide bond of Autographa californica multicapsid nucleopolyhedrovirus GP64 is not essential for membrane fusion and virion budding. J Virol 2010; 84:8584-95. [PMID: 20573818 DOI: 10.1128/jvi.00264-10] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The GP64 envelope glycoprotein of the Autographa californica nucleopolyhedrovirus (AcMNPV) is a class III viral membrane fusion protein that is triggered by low pH during entry. Unlike most other viral fusion protein trimers, the monomers of GP64 are covalently linked to each other within the trimer by a single intermolecular disulfide bond (Cys24 Cys372). Single or paired alanine substitutions for Cys24 and Cys372 resulted in lower-efficiency transport of GP64 to the cell surface. Surprisingly, these mutated GP64s induced syncytium formation, and normalized fusion activities were approximately 30% of that from wild-type (WT) GP64. Heat treatment (37 degrees C) did not further reduce fusion activity of GP64 constructs with a disrupted intermolecular disulfide bond, suggesting that the GP64 trimers were relatively thermostable in the absence of the intermolecular disulfide bond. In addition, analysis of binding by a conformation-specific monoclonal antibody (MAb) suggested that the low-pH-induced refolding of those GP64 constructs was generally similar to that of WT GP64. In addition to its critical role in membrane fusion, GP64 is also necessary for efficient budding. When GP64 constructs containing a disrupted intermolecular disulfide bond (Cys24 Cys372) were displayed at the cell surface at levels comparable to those of WT GP64, virion budding efficiency ranged from approximately 39 to 88%, indicating that the intermolecular disulfide bond is not required for virion budding. However, GP64 proteins with a disrupted intermolecular disulfide could not rescue a GP64-null bacmid. We also examined the 6 conserved intramolecular disulfide bonds using single and paired alanine substitution mutations. None of the GP64 constructs with disrupted intramolecular disulfide bonds were capable of mediating pH-triggered membrane fusion, indicating that the intramolecular disulfide bonds are all necessary for membrane fusion. Thus, while the intramolecular disulfide bonds of GP64 appear to serve critical roles in membrane fusion, the unusual intermolecular disulfide bond was not critical for membrane fusion or virion budding yet appears to play an unknown role in viral infectivity.
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Influence of disulfide-stabilized structure on the specificity of helper T-cell and antibody responses to HIV envelope glycoprotein gp120. J Virol 2010; 84:3303-11. [PMID: 20089653 DOI: 10.1128/jvi.02242-09] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
CD4(+) helper T cells specific for human immunodeficiency virus type 1 (HIV-1) are associated with control of viremia. Nevertheless, vaccines have had limited effectiveness thus far, in part because sequence variability and other structural features of the HIV envelope glycoprotein deflect the immune response. Previous studies indicated that CD4(+) T-cell epitope dominance is controlled by antigen three-dimensional structure through its influence on antigen processing and presentation. In this work, three disulfide bonds in the outer domain of gp120 were individually deleted in order to destabilize the local three-dimensional structure and enhance the presentation of nearby weakly immunogenic epitopes. However, upon immunization of groups of BALB/c mice, the CD4(+) T-cell response was broadly reduced for all three variants, and distinct epitope profiles emerged. For one variant, antibody titers were sharply increased, and the antibody exhibited significant CD4-blocking activity.
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Sanders RW, Hsu STD, van Anken E, Liscaljet IM, Dankers M, Bontjer I, Land A, Braakman I, Bonvin AMJJ, Berkhout B. Evolution rescues folding of human immunodeficiency virus-1 envelope glycoprotein GP120 lacking a conserved disulfide bond. Mol Biol Cell 2008; 19:4707-16. [PMID: 18753405 PMCID: PMC2575144 DOI: 10.1091/mbc.e08-07-0670] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2008] [Accepted: 08/19/2008] [Indexed: 11/11/2022] Open
Abstract
The majority of eukaryotic secretory and membrane proteins contain disulfide bonds, which are strongly conserved within protein families because of their crucial role in folding or function. The exact role of these disulfide bonds during folding is unclear. Using virus-driven evolution we generated a viral glycoprotein variant, which is functional despite the lack of an absolutely conserved disulfide bond that links two antiparallel beta-strands in a six-stranded beta-barrel. Molecular dynamics simulations revealed that improved hydrogen bonding and side chain packing led to stabilization of the beta-barrel fold, implying that beta-sheet preference codirects glycoprotein folding in vivo. Our results show that the interactions between two beta-strands that are important for the formation and/or integrity of the beta-barrel can be supported by either a disulfide bond or beta-sheet favoring residues.
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Affiliation(s)
- Rogier W Sanders
- Laboratory of Experimental Virology, Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
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Optimization of human immunodeficiency virus type 1 envelope glycoproteins with V1/V2 deleted, using virus evolution. J Virol 2008; 83:368-83. [PMID: 18922866 DOI: 10.1128/jvi.01404-08] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human immunodeficiency virus type 1 envelope glycoprotein (Env) complex is the principal focus of neutralizing antibody-based vaccines. The functional Env complex is a trimer consisting of six individual subunits: three gp120 molecules and three gp41 molecules. The individual subunits have proven unsuccessful as vaccines presumably because they do not resemble the functional Env complex. Variable domains and carbohydrates shield vulnerable neutralization epitopes on the functional Env complex. The deletion of variable loops has been shown to improve gp120's immunogenicity; however, problems have been encountered when introducing such modifications in stabilized Env trimer constructs. To address these issues, we have created a set of V1/V2 and V3 loop deletion variants in the context of complete virus to allow optimization by forced virus evolution. Compensatory second-site substitutions included the addition and/or removal of specific carbohydrates, changes in the disulfide-bonded architecture of the V1/V2 stem, the replacement of hydrophobic residues by hydrophilic and charged residues, and changes in distal parts of gp120 and gp41. These viruses displayed increased sensitivity to neutralizing antibodies, demonstrating the improved exposure of conserved domains. The results show that we can select for functionally improved Env variants with loop deletions through forced virus evolution. Selected evolved Env variants were transferred to stabilized Env trimer constructs and were shown to improve trimer expression and secretion. Based on these findings, we can make recommendations on how to delete the V1/V2 domain from recombinant Env trimers for vaccine and X-ray crystallography studies. In general, virus evolution may provide a powerful tool to optimize Env vaccine antigens.
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