Stabilizing the HIV-1 envelope glycoprotein State 2A conformation

• Published in: Journal of virology Vol. 95; no. 5
• Main Authors: Vézina, Dani, Gong, Shang Yu, Tolbert, William D, Ding, Shilei, Nguyen, Dung, Richard, Jonathan, Gendron-Lepage, Gabrielle, Melillo, 3rd, Bruno, Smith, Amos B, Pazgier, Marzena, Finzi, Andrés
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.03.2021
• Subjects: Pathogenesis and Immunity; HIV-1; soluble CD4; small CD4 mimetics; CD4-induced antibodies; nonneutralizing antibodies; State 2A; cluster A; envelope glycoproteins; gp120; Env conformation; coreceptor binding site
• ISSN: 0022-538X; 1098-5514
• DOI: 10.1128/JVI.01620-20

The HIV-1 envelope glycoprotein (Env) trimer [(gp120/gp41) ] is a metastable complex expressed at the surface of viral particles and infected cells that samples different conformations. Before engaging CD4, Env adopts an antibody-resistant "closed" conformation (State 1). CD4 binding triggers an intermediate conformation (State 2) and then a more "open" conformation (State 3) that can be recognized by non-neutralizing antibodies (nnAbs) such as those that recognize the coreceptor binding site (CoRBS). Binding of antibodies to the CoRBS permits another family of nnAbs, the anti-cluster A family of Abs which target the gp120 inner domain, to bind and stabilize an asymmetric conformation (State 2A). Cells expressing Env in this conformation are susceptible to antibody-dependent cellular cytotoxicity (ADCC). This conformation can be stabilized by small-molecule CD4 mimetics (CD4mc) or soluble CD4 (sCD4) in combination with anti-CoRBS Ab and anti-cluster A antibodies. The precise stoichiometry of each component that permits this sequential opening of Env remains unknown. Here, we used a cell-based ELISA (CBE) assay to evaluate each component individually. In this assay we used a "trimer mixing" approach by combining wild-type (wt) subunits with subunits impaired for CD4 or CoRBS Ab binding. This enabled us to show that State 2A requires all three gp120 subunits to be bound by sCD4/CD4mc and anti-CoRBS Abs. Two of these subunits can then bind anti-cluster A Abs. Altogether, our data suggests how this antibody vulnerable Env conformation is stabilized. Stabilization of HIV-1 Env State 2A has been shown to sensitize infected cells to ADCC. State 2A can be stabilized by a "cocktail" composed of CD4mc, anti-CoRBS and anti-cluster A Abs. We present evidence that optimal State 2A stabilization requires all three gp120 subunits to be bound by both CD4mc and anti-CoRBS Abs. Our study provides valuable information on how to stabilize this ADCC-vulnerable conformation. Strategies aimed at stabilizing State 2A might have therapeutic utility.