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Moscoso CG, Xing L, Hui J, Hu J, Kalkhoran MB, Yenigun OM, Sun Y, Paavolainen L, Martin L, Vahlne A, Zambonelli C, Barnett SW, Srivastava IK, Cheng RH. Trimeric HIV Env provides epitope occlusion mediated by hypervariable loops. Sci Rep 2014; 4:7025. [PMID: 25395053 PMCID: PMC4231788 DOI: 10.1038/srep07025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Accepted: 08/26/2014] [Indexed: 12/17/2022] Open
Abstract
Hypervariable loops of HIV-1 Env protein gp120 are speculated to play roles in the conformational transition of Env to the receptor binding-induced metastable state. Structural analysis of full-length Env-based immunogens, containing the entire V2 loop, displayed tighter association between gp120 subunits, resulting in a smaller trimeric diameter than constructs lacking V2. A prominent basal quaternary location of V2 and V3′ that challenges previous reports would facilitate gp41-independent gp120-gp120 interactions and suggests a quaternary mechanism of epitope occlusion facilitated by hypervariable loops. Deletion of V2 resulted in dramatic exposure of basal, membrane-proximal gp41 epitopes, consistent with its predicted basal location. The structural features of HIV-1 Env characterized here provide grounds for a paradigm shift in loop exposure and epitope occlusion, while providing substantive rationale for epitope display required for elicitation of broadly neutralizing antibodies, as well as substantiating previous pertinent literature disregarded in recent reports.
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Affiliation(s)
- Carlos G Moscoso
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Li Xing
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Jinwen Hui
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Jeffrey Hu
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | | | - Onur M Yenigun
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Yide Sun
- Novartis Vaccines and Diagnostics Inc., 45 Sydney Street, Cambridge, MA 02139
| | - Lassi Paavolainen
- Department of Biological and Environmental Science/Nanoscience Center, University of Jyväskylä, FI-40351 Jyväskylä, Finland
| | - Loïc Martin
- Commissariat à l'énergie atomique et aux énergies alternatives, Institut de Biologie et Technologies de Saclay, Service d'Ingénierie Moléculaire des Protéines, Gif-sur-Yvette F-91191, France
| | - Anders Vahlne
- Karolinska Institutet, Structural Virology, Clinical Microbiology/University Hospital, 171 77 Stockholm, Sweden
| | - Carlo Zambonelli
- Novartis Vaccines and Diagnostics Inc., 45 Sydney Street, Cambridge, MA 02139
| | - Susan W Barnett
- Novartis Vaccines and Diagnostics Inc., 45 Sydney Street, Cambridge, MA 02139
| | | | - R Holland Cheng
- 1] Department of Molecular and Cellular Biology, University of California, Davis, CA 95616 [2] Karolinska Institutet, Structural Virology, Clinical Microbiology/University Hospital, 171 77 Stockholm, Sweden
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Stabilizing exposure of conserved epitopes by structure guided insertion of disulfide bond in HIV-1 envelope glycoprotein. PLoS One 2013; 8:e76139. [PMID: 24146829 PMCID: PMC3797752 DOI: 10.1371/journal.pone.0076139] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Accepted: 08/26/2013] [Indexed: 11/19/2022] Open
Abstract
Entry of HIV-1 into target cells requires binding of the viral envelope glycoprotein (Env) to cellular receptors and subsequent conformational changes that culminates in fusion of viral and target cell membranes. Recent structural information has revealed that these conformational transitions are regulated by three conserved but potentially flexible layers stacked between the receptor-binding domain (gp120) and the fusion arm (gp41) of Env. We hypothesized that artificial insertion of a covalent bond will ‘snap’ Env into a conformation that is less mobile and stably expose conserved sites. Therefore, we analyzed the interface between these gp120 layers (layers 1, 2 and 3) and identified residues that may form disulfide bonds when substituted with cysteines. We subsequently probed the structures of the resultant mutant gp120 proteins by assaying their binding to a variety of ligands using Surface Plasmon Resonance (SPR) assay. We found that a single disulfide bond strategically inserted between the highly conserved layers 1 and 2 (C65-C115) is able to ‘lock’ gp120 in a CD4 receptor bound conformation (in the absence of CD4), as indicated by the lower dissociation constant (Kd) for the CD4-induced (CD4i) epitope binding 17b antibody. When disulfide-stabilized monomeric (gp120) and trimeric (gp140) Envs were used to immunize rabbits, they were found to elicit a higher proportion of antibodies directed against both CD4i and CD4 binding site epitopes than the wild-type proteins. These results demonstrate that structure-guided stabilization of inter-layer interactions within HIV-1 Env can be used to expose conserved epitopes and potentially overcome the sequence diversity of these molecules.
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