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Quaternary contact in the initial interaction of CD4 with the HIV-1 envelope trimer.

ABSTRACT: Binding of the gp120 envelope (Env) glycoprotein to the CD4 receptor is the first step in the HIV-1 infectious cycle. Although the CD4-binding site has been extensively characterized, the initial receptor interaction has been difficult to study because of major CD4-induced structural rearrangements. Here we used cryogenic electron microscopy (cryo-EM) to visualize the initial contact of CD4 with the HIV-1 Env trimer at 6.8-Å resolution. A single CD4 molecule is embraced by a quaternary HIV-1-Env surface formed by coalescence of the previously defined CD4-contact region with a second CD4-binding site (CD4-BS2) in the inner domain of a neighboring gp120 protomer. Disruption of CD4-BS2 destabilized CD4-trimer interaction and abrogated HIV-1 infectivity by preventing the acquisition of coreceptor-binding competence. A corresponding reduction in HIV-1 infectivity occurred after the mutation of CD4 residues that interact with CD4-BS2. Our results document the critical role of quaternary interactions in the initial HIV-Env-receptor contact, with implications for treatment and vaccine design.

SUBMITTER: Liu Q

PROVIDER: S-EPMC5798227 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Quaternary contact in the initial interaction of CD4 with the HIV-1 envelope trimer.

Liu Qingbo Q Acharya Priyamvada P Dolan Michael A MA Zhang Peng P Guzzo Christina C Lu Jacky J Kwon Alice A Gururani Deepali D Miao Huiyi H Bylund Tatsiana T Chuang Gwo-Yu GY Druz Aliaksandr A Zhou Tongqing T Rice William J WJ Wigge Christoph C Carragher Bridget B Potter Clinton S CS Kwong Peter D PD Lusso Paolo P

Nature structural & molecular biology 20170220 4

Binding of the gp120 envelope (Env) glycoprotein to the CD4 receptor is the first step in the HIV-1 infectious cycle. Although the CD4-binding site has been extensively characterized, the initial receptor interaction has been difficult to study because of major CD4-induced structural rearrangements. Here we used cryogenic electron microscopy (cryo-EM) to visualize the initial contact of CD4 with the HIV-1 Env trimer at 6.8-Å resolution. A single CD4 molecule is embraced by a quaternary HIV-1-Env ...[more]

PMID: 28218750

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Project description:The first step in HIV-1 entry is the attachment of the envelope (Env) trimer to target cell CD4. As such, the CD4-binding site (CD4bs) remains one of the few universally accessible sites for antibodies (Abs). We recently described a method of isolating Abs directly from the circulating plasma and described a panel of broadly neutralizing Abs (bnAbs) from an HIV-1 "elite neutralizer" referred to as patient N49 (N49 Ab lineage [M. M. Sajadi, A. Dashti, Z. R. Tehrani, W. D. Tolbert, et al., Cell 173:1783-1795.e14, 2018, https://doi.org/10.1016/j.cell.2018.03.061]). Here, we describe the molecular details of antigen recognition by N49P6, an Ab of the N49 lineage that recapitulates most of the neutralization breadth and potency of the donor's plasma IgG. Our studies done in the context of monomeric and trimeric antigens indicate that N49P6 combines many characteristics of known CD4bs-specific bnAbs with features that are unique to the N49 Ab lineage to achieve its remarkable neutralization breadth. These include the omission of the CD4 Phe43 cavity and dependence instead on interactions with highly conserved gp120 inner domain layer 3. Interestingly, when bound to BG505 SOSIP, N49P6 closely mimics the initial contact of host receptor CD4 to the adjacent promoter of the HIV-1 Env trimer to lock the trimer in the closed conformation. Altogether, N49P6 defines a new class of near-pan-neutralizing, plasma deconvoluted CD4bs Abs that we refer to as the N49P series. The details of the mechanisms of action of this new Ab class pave the way for the next generation of HIV-1 bnAbs that can be used as vaccine components of therapeutics. IMPORTANCE Binding to target cell CD4 is the first crucial step required for HIV-1 infection. Thus, the CD4-binding site (CD4bs) is one of the most accessible sites for antibodies (Abs). However, due to steric constraints, only a few Abs are capable of targeting this site. Here, we show that the exceptional neutralization breadth and potency of N49P6, a near-pan-neutralizing Ab targeting the CD4bs isolated from the plasma of an HIV-1 "elite neutralizer," patient N49, are due to its signature combination of more typical CD4bs Ab-binding characteristics with unique interactions with the highly conserved gp120 inner domain. In addition, we also present a structural analysis of N49P6 in complex with the BG505 SOSIP trimer to show that N49P6 exhibits remarkable breadth in part by mimicking CD4's quaternary interaction with the neighboring gp120 protomer. In its mode of antigen interaction, N49P6 is unique and represents a new class of CD4bs-specific bnAbs.

Project description:Chimeric simian immunodeficiency virus (SIV)/human immunodeficiency virus (HIV) (SHIV) infection of macaques is commonly used to model HIV type 1 (HIV-1) transmission and pathogenesis in humans. Despite the fact that SHIVs encode SIV antagonists of the known macaque host restriction factors, these viruses require additional adaptation for replication in macaques to establish a persistent infection. Additional adaptation may be required in part because macaque CD4 (mCD4) is a suboptimal receptor for most HIV-1 envelope glycoprotein (Env) variants. This requirement raises the possibility that adaptation of HIV-1 Env to the macaque host leads to selection of variants that lack important biological and antigenic properties of the viruses responsible for the HIV-1 pandemic in humans. Here, we investigated whether this adaptation process leads to changes in the antigenicity and structure of HIV-1 Env. For this purpose, we examined how two independent mutations that enhance mCD4-mediated entry, A204E and G312V, impact antibody recognition in the context of seven different parental HIV-1 Env proteins from diverse subtypes. We also examined HIV-1 Env variants from three SHIVs that had been adapted for increased replication in macaques. Our results indicate that these different macaque-adapted variants had features in common, including resistance to antibodies directed to quaternary epitopes and sensitivity to antibodies directed to epitopes in the variable domains (V2 and V3) that are buried in the parental, unadapted Env proteins. Collectively, these findings suggest that adaptation to mCD4 results in conformational changes that expose epitopes in the variable domains and disrupt quaternary epitopes in the native Env trimer.These findings indicate the antigenic consequences of adapting HIV-1 Env to mCD4. They also suggest that to best mimic HIV-1 infection in humans when using the SHIV/macaque model, HIV-1 Env proteins should be identified that use mCD4 as a functional receptor and preserve quaternary epitopes characteristic of HIV-1 Env.

Project description:The HIV-1 envelope trimer (Env) is the target of broadly neutralizing antibodies and is being explored as a vaccine candidate to elicit protective antibodies. One of the most promising antigenic and structural mimics of HIV-1 Env is the SOSIP.664-stabilized soluble trimer from the clade A strain BG505, which is preferentially recognized by broadly neutralizing antibodies. Trimer immunization elicits high-titer neutralization of the autologous tier 2 BG505 strain; however, breadth is limited, and substantial interest has focused on understanding and improving trimer immunogenicity. We sought to improve the antigenic specificity of BG505 SOSIP.664 by reducing recognition of the variable loop 3 (V3) region, which elicits only weakly neutralizing antibodies. To stabilize the trimer in its prefusion closed conformation, we complexed trimeric BG505 SOSIP.664 with the antigen-binding fragment (Fab) of PGT145, a broadly neutralizing quaternary-structure-specific antibody. Compared to the ligand-free trimer, the PGT145 Fab-BG505 SOSIP.664 complex displayed increased melting temperature stability and reduced V3 recognition. In guinea pigs, immunization with the PGT145 Fab-BG505 SOSIP.664 complex elicited ?100-fold lower V3-directed binding and neutralization titers than those obtained with ligand-free BG505 SOSIP.664. Both complexed and ligand-free BG505 SOSIP.664 elicited comparable neutralization of the autologous BG505 virus, and in both cases, BG505 neutralization mapped to the outer domain of gp120 for some guinea pigs. Our results indicate that it is possible to reduce immune recognition of the V3 region of the trimer while maintaining the antigenic profile needed to induce autologous neutralizing antibodies. These data suggest that appropriate modifications of trimer immunogens could further focus the immune response on key neutralization epitopes.HIV-1 Env trimers have been proposed as preferred HIV-1 vaccine immunogens. One version, BG505 SOSIP.664, a soluble stabilized trimer, was recently shown to elicit high-titer autologous neutralizing antibodies (NAbs) in rabbits. Here we compared two immunogens: the ligand-free BG505 SOSIP.664 trimer and the same trimer bound to the antigen-binding fragment (Fab) of the PGT145 antibody, a broadly neutralizing antibody which recognizes the trimer at its membrane-distal apex. We hypothesized that the Fab-bound complex would stabilize BG505 SOSIP.664 in its prefusion closed conformation and limit reactivity to weakly neutralizing antibodies targeting the variable loop 3 (V3) region. In guinea pigs, the Fab-complexed trimer induced 100-fold lower responses to the V3 region, while both ligand-free and Fab-complexed trimers elicited similar levels of autologous NAbs. Our findings demonstrate the potential to reduce "off-target" immunogenicity while maintaining the capacity to generate autologous NAbs.

Dataset Information

Quaternary contact in the initial interaction of CD4 with the HIV-1 envelope trimer.

Publications

Quaternary contact in the initial interaction of CD4 with the HIV-1 envelope trimer.

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