The remarkable diversity, glycosylation and conformational flexibility of the human immunodeficiency virus type 1 (HIV-1) envelope (Env), including substantial rearrangement of the gp120 glycoprotein upon binding the CD4 receptor, allow it to evade antibody-mediated neutralization. Despite this complexity, the HIV-1 Env must retain conserved determinants that mediate CD4 binding. To evaluate how these determinants might provide opportunities for antibody recognition, we created variants of gp120 stabilized in the CD4-bound state, assessed binding of CD4 and of receptor-binding-site antibodies, and determined the structure at 2.3 Å resolution of the broadly neutralizing antibody b12 in complex with gp120. b12 binds to a conformationally invariant surface that overlaps a distinct subset of the CD4-binding site. This surface is involved in the metastable attachment of CD4, before the gp120 rearrangement required for stable engagement. A site of vulnerability, related to a functional requirement for efficient association with CD4, can therefore be targeted by antibody to neutralize HIV-1.

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We thank B. Graham, D. Hamer, S. Harrison, R. Pantophlet, W. Schief, L. Shapiro, I. Wilson and members of the Structural Biology Section, VRC, for discussions and comments on the manuscript; M. Gao for assistance with PDB deposit; H. Katinger for antibody 2G12; G. Lin for suggesting the use of swainsonine; S. Majeed for preparation of Fab 17b; J. Nelson for assistance with b12 ELISAs; M. Posner for antibody F105; J. Robinson for antibodies 17b, 1.5e and F91; J. Stuckey for assistance with figures; M. Venturi for assistance with gp120 production methodology; and the NIH AIDS Research and Reference Reagent Program for CD4. Support for this work was provided by the Intramural Research Program of the NIH, by the International AIDS Vaccine Initiative, by a grant from the Bill and Melinda Gates Foundation Grand Challenges in Global Heath Initiative, and by grants from the NIH. Use of SER-CAT at the Advanced Photon Source was supported by the US Department of Energy, Basic Energy Sciences, Office of Science.

Author Contributions T.Z. and P.D.K. carried out structure-based stabilization, SPR analyses and structural determinations; L.X. and G.J.N. constructed gp120 substitutions and developed and implemented a high-throughput gp120-production system suitable for crystallization; B.D. and R.W. carried out ITC characterizations; A.J.H., M.B.Z. and D.R.B. provided b12, b3, b6, b11 and b13, and mutant b12 binding; D.V.R. and J.A. provided D1D2-Igαtp and associated SPR analyses; S.-H.X., X.Y. and J.S. provided OD1 and preliminary design and antigenic analyses; and M.-Y.Z. and D.S.D. provided m6, m14 and m18. All authors contributed to the manuscript preparation.

Coordinates and structure factors have been deposited in the Protein Data Bank and may be obtained from the authors (accession codes 2nxy–2ny6 for the nine variant gp120 molecules with CD4 and 17b; accession code 2ny7 for the b12–gp120 complex)

Author information


  1. Vaccine Research Center, and,

    • Tongqing Zhou
    • , Ling Xu
    • , Barna Dey
    • , Richard Wyatt
    • , Gary J. Nabel
    •  & Peter D. Kwong
  2. Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA

    • Donald Van Ryk
    •  & James Arthos
  3. Departments of Immunology and Molecular Biology, Scripps Research Institute, La Jolla, California 92037, USA

    • Ann J. Hessell
    • , Michael B. Zwick
    •  & Dennis R. Burton
  4. Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA

    • Shi-Hua Xiang
    • , Xinzhen Yang
    •  & Joseph Sodroski
  5. Center for Cancer Research, National Cancer Institute, Frederick, Maryland 21702, USA

    • Mei-Yun Zhang
    •  & Dimiter S. Dimitrov


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Competing interests

Coordinates and structure factors have been deposited in the Protein Data Bank and may be obtained from the authors (accession codes 2nxy–2ny6 for the nine variant gp120 molecules with CD4 and 17b; accession code 2ny7 for the b12–gp120 complex). Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

Corresponding author

Correspondence to Peter D. Kwong.

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