Asymmetric recognition of HIV-1 Envelope trimer by V1V2 loop-targeting antibodies

Creators: Wang, Haoqing; Gristick, Harry B.; Scharf, Louise; West, Anthony P., Jr.; Galimidi, Rachel P.; Seaman, Michael S.; Freund, Natalia T.; Nussenzweig, Michel C.; Bjorkman, Pamela J.

Abstract

The HIV-1 envelope (Env) glycoprotein binds to host cell receptors to mediate membrane fusion. The prefusion Env trimer is stabilized by V1V2 loops that interact at the trimer apex. Broadly neutralizing antibodies (bNAbs) against V1V2 loops, exemplified by PG9, bind asymmetrically as a single Fab to the apex of the symmetric Env trimer using a protruding CDRH3 to penetrate the Env glycan shield. Here we characterized a distinct mode of V1V2 epitope recognition by the new bNAb BG1 in which two Fabs bind asymmetrically per Env trimer using a compact CDRH3. Comparisons between cryo-EM structures of Env trimer complexed with BG1 (6.2 Å resolution) and PG9 (11.5 Å resolution) revealed a new V1V2-targeting strategy by BG1. Analyses of the EM structures provided information relevant to vaccine design including molecular details for different modes of asymmetric recognition of Env trimer and a binding model for BG1 recognition of V1V2 involving glycan flexibility.

Additional Information

© 2017, Wang et al. This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited. Received April 01, 2017; Accepted May 24, 2017; Published May 26, 2017. We thank Zhiheng Yu, Chuan Hong, and Rick Huang (Janelia Farm) and Mark Yeager and Kelly Dryden (University of Virginia) for assistance with cryo-EM data collection and motion correction, Alasdair McDowall and Songye Chen for training in cryo-EM techniques and data processing, and the Gordon and Betty Moore and Beckman Foundations for gifts to Caltech to support electron microscopy and to the Caltech Molecular Observatory to support X-ray crystallography. Cryo-EM data for the PG9-Env-8ANC195 complex structure was collected at the Molecular Electron Microscopy Core facility at the University of Virginia, which is supported by the School of Medicine and an NIH grant (G20-RR31199). The Titan Krios microscope and Falcon II direct detector used for data collection at University of Virginia was supported by NIH SIG grant S10-RR025067 and NIH SIG S10-OD018149. Operations at the Stanford Synchrotron Radiation Lightsource are supported by the US Department of Energy and the National Institutes of Health. We also thank Jost Vielmetter and the Caltech Protein Expression Center for transfections and protein expression, and members of the P.J.B. and M.C.N. laboratories for helpful discussions and critical reading of the manuscript. This research was supported by the National Institutes of Health Grant 2 P50 GM082545-06 (to P.J.B.), National Institute Of Allergy and Infectious Diseases of the National Institutes of Health Grant HIVRAD P01 AI100148 (to P.J.B. and M.C.N.), the Bill and Melinda Gates Foundation Collaboration for AIDS Vaccine Discovery Grant 1040753 (to M.C.N. and P.J.B.), and a Comprehensive Antibody-Vaccine Immune Monitoring Consortium Grant 1032144 (M.S.S.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Author contributions: HW, Data curation, Formal analysis, Validation, Investigation, Visualization, Writing—original draft, Writing—review and editing, Solved and analyzed EM structures; HBG, Conceptualization, Data curation, Formal analysis, Validation, Investigation, Visualization, Writing—review and editing, Analyzed SEC-MALS experiments; LS, Data curation, Formal analysis, Validation, Investigation, Visualization, Solved the BG1 Fab crystal structure; APW, Conceptualization, Data curation, Formal analysis, Validation, Investigation, Visualization, Writing—review and editing, Performed computational and bioinformatics analyses. Analyzed MNR data; RPG, Data curation, Formal analysis, Investigation, Analyzed MNR data; MSS, Data curation, Conducted in vitro neutralization assays; NTF, Resources, Writing—review and editing, Isolated and characterized the BG1 IgG bNAb; MCN, Conceptualization, Resources, Data curation, Formal analysis, Supervision, Funding acquisition, Investigation, Writing—review and editing, Isolated and characterized the BG1 IgG bNAb; PJB, Conceptualization, Data curation, Formal analysis, Supervision, Funding acquisition, Validation, Investigation, Visualization, Methodology, Writing—original draft, Project administration, Writing—review and editing. No competing interests declared.

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