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      HIV-1 R5 Macrophage-Tropic Envelope Glycoprotein Trimers Bind CD4 with High Affinity, while the CD4 Binding Site on Non-macrophage-tropic, T-Tropic R5 Envelopes Is Occluded

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          HIV-1 R5 variants exploit CCR5 as a coreceptor to infect both T cells and macrophages. R5 viruses that are transmitted or derived from immune tissue and peripheral blood are mainly inefficient at mediating infection of macrophages. In contrast, highly macrophage-tropic (mac-tropic) R5 viruses predominate in brain tissue and can be detected in cerebrospinal fluid but are infrequent in immune tissue or blood even in late disease. These mac-tropic R5 variants carry envelope glycoproteins (Envs) adapted to exploit low levels of CD4 on macrophages to induce infection. However, it is unclear whether this adaptation is conferred by an increased affinity of the Env trimer for CD4 or is mediated by postbinding structural rearrangements in the trimer that enhance the exposure of the coreceptor binding site and facilitate events leading to fusion and virus entry. In this study, we investigated CD4 binding to mac-tropic and non-mac-tropic Env trimers and showed that CD4-IgG binds efficiently to mac-tropic R5 Env trimers, while binding to non-mac-tropic trimers was undetectable. Our data indicated that the CD4 binding site (CD4bs) is highly occluded on Env trimers of non-mac-tropic R5 viruses. Such viruses may therefore infect T cells via viral synapses where Env and CD4 become highly concentrated. This environment will enable high-avidity interactions that overcome extremely low Env-CD4 affinities.

          IMPORTANCE HIV R5 variants bind to CD4 and CCR5 receptors on T cells and macrophages to initiate infection. Transmitted HIV variants infect T cells but not macrophages, and these viral strains persist in immune tissue even in late disease. Here we show that the binding site for CD4 present on HIV's envelope protein is occluded on viruses replicating in immune tissue. This occlusion likely prevents antibody binding to this site and neutralization of the virus, but it makes it difficult for virus-CD4 interactions to occur. Such viruses probably pass from T cell to T cell via cell contacts where CD4 is highly concentrated and allows infection via inefficient envelope-CD4 binding. Our data are highly relevant for vaccines that aim to induce antibodies targeting the CD4 binding site on the envelope protein.

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          Author and article information

          Role: Editor
          J Virol
          J. Virol
          Journal of Virology
          American Society for Microbiology (1752 N St., N.W., Washington, DC )
          8 November 2017
          2 January 2018
          15 January 2018
          : 92
          : 2
          [a ]Program in Molecular Medicine, University of Massachusetts Medical School, Biotech 2, Worcester, Massachusetts, USA
          [b ]Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA
          Ulm University Medical Center
          Author notes
          Address correspondence to Paul R. Clapham, paul.clapham@ 123456umassmed.edu .

          Present address: Paul J. Peters, Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, Massachusetts, USA; Aaron Wallace, MassBiologics, Mattapan, Massachusetts, USA.

          Citation Quitadamo B, Peters PJ, Repik A, O'Connell O, Mou Z, Koch M, Somasundaran M, Brody R, Luzuriaga K, Wallace A, Wang S, Lu S, McCauley S, Luban J, Duenas-Decamp M, Gonzalez-Perez MP, Clapham PR. 2018. HIV-1 R5 macrophage-tropic envelope glycoprotein trimers bind CD4 with high affinity, while the CD4 binding site on non-macrophage-tropic, T-tropic R5 envelopes is occluded. J Virol 92:e00841-17. https://doi.org/10.1128/JVI.00841-17.

          PMC5752949 PMC5752949 5752949 00841-17
          Copyright © 2018 American Society for Microbiology.
          Page count
          Figures: 4, Tables: 2, Equations: 0, References: 54, Pages: 14, Words: 8426
          Funded by: HHS | NIH | National Institute of Allergy and Infectious Diseases (NIAID), https://doi.org/10.13039/100000060;
          Award ID: AI089334
          Award ID: AI082274
          Award ID: AI097267
          Award ID: AI111804
          Award ID: AI127231
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          Funded by: HHS | NIH | National Institute on Drug Abuse (NIDA), https://doi.org/10.13039/100000026;
          Award ID: DA034990
          Award Recipient : Award Recipient :
          Funded by: HHS | NIH | National Institute of Neurological Disorders and Stroke (NINDS), https://doi.org/10.13039/100000065;
          Award ID: NS095749
          Award ID: NS084910
          Award ID: NS097145
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          Virus-Cell Interactions
          Custom metadata
          January 2018

          envelope glycoprotein, macrophage tropism, HIV, CD4, CD4bs, CCR5


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