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Changes in Structure and Antigenicity of HIV-1 Env Trimers Resulting from Removal of a Conserved CD4 Binding Site-Proximal Glycan.

ABSTRACT: The envelope glycoprotein (Env) is the major target for HIV-1 broadly neutralizing antibodies (bNAbs). One of the mechanisms that HIV has evolved to escape the host's immune response is to mask conserved epitopes on Env with dense glycosylation. Previous studies have shown that the removal of a particular conserved glycan at N197 increases the neutralization sensitivity of the virus to antibodies targeting the CD4 binding site (CD4bs), making it a site of significant interest from the perspective of vaccine design. At present, the structural consequences that result from the removal of the N197 glycan have not been characterized. Using native-like SOSIP trimers, we examine the effects on antigenicity and local structural dynamics resulting from the removal of this glycan. A large increase in the binding of CD4bs and V3-targeting antibodies is observed for the N197Q mutant in trimeric Env, while no changes are observed with monomeric gp120. While the overall structure and thermostability are not altered, a subtle increase in the flexibility of the variable loops at the trimeric interface of adjacent protomers is evident in the N197Q mutant by hydrogen-deuterium exchange mass spectrometry. Structural modeling of the glycan chains suggests that the spatial occupancy of the N197 glycan leads to steric clashes with CD4bs antibodies in the Env trimer but not monomeric gp120. Our results indicate that the removal of the N197 glycan enhances the exposure of relevant bNAb epitopes on Env with a minimal impact on the overall trimeric structure. These findings present a simple modification for enhancing trimeric Env immunogens in vaccines.The HIV-1 Env glycoprotein presents a dense patchwork of host cell-derived N-linked glycans. This so-called glycan shield is considered to be a major protective mechanism against immune recognition. While the positions of many N-linked glycans are isolate specific, some are highly conserved and are believed to play key functional roles. In this study, we examine the conserved, CD4 binding site-proximal N197 glycan and demonstrate that its removal both facilitates neutralizing antibody access to the CD4 binding site and modestly impacts the structural dynamics at the trimer crown without drastically altering global Env trimer stability. This indicates that surgical glycosylation site modification may be an effective way of sculpting epitope presentation in Env-based vaccines.

SUBMITTER: Liang Y

PROVIDER: S-EPMC5044814 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Changes in Structure and Antigenicity of HIV-1 Env Trimers Resulting from Removal of a Conserved CD4 Binding Site-Proximal Glycan.

Liang Yu Y Guttman Miklos M Williams James A JA Verkerke Hans H Alvarado Daniel D Hu Shiu-Lok SL Lee Kelly K KK

Journal of virology 20160929 20

<h4>Unlabelled</h4>The envelope glycoprotein (Env) is the major target for HIV-1 broadly neutralizing antibodies (bNAbs). One of the mechanisms that HIV has evolved to escape the host's immune response is to mask conserved epitopes on Env with dense glycosylation. Previous studies have shown that the removal of a particular conserved glycan at N197 increases the neutralization sensitivity of the virus to antibodies targeting the CD4 binding site (CD4bs), making it a site of significant interest ...[more]

PMID: 27489265

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Project description:Native-like trimers of the SOSIP design are being developed as immunogens in human immunodeficiency virus type 1 (HIV-1) vaccine development programs. These trimers display the epitopes for multiple broadly neutralizing antibodies (bNAbs) but can also expose binding sites for some types of nonneutralizing antibodies (non-NAbs). Among the latter are epitopes in the gp120 V3 region that are highly immunogenic when SOSIP trimers are evaluated in animal models. It is presently uncertain whether antibodies against V3 can interfere with the induction of NAbs, but there are good arguments in favor of suppressing such "off-target" immune responses. Accordingly, we have assessed how to minimize the exposure of V3 non-NAb epitopes and thereby reduce their immunogenicity by introducing N-glycans within the V3 region of BG505 SOSIP trimers. We found that inserting glycans at positions 306 and 314 (termed M1 and M7) markedly reduced V3 antigenicity while improving the presentation of trimer apex bNAb epitopes. Both added glycans were shown to be predominantly of the Man6GlcNAc2 form. The additional introduction of the E64K ground-state stabilizing substitution markedly reduced or ablated soluble CD4 (sCD4) induction of non-NAb epitopes in V3 and/or associated with the coreceptor binding site. When a V3 glycan- and E64K-modified trimer variant, BG505 SOSIP.664-E64K.M1M7, was tested in rabbits, V3 immunogenicity was eliminated while the autologous NAb response was unchanged.IMPORTANCE Trimeric proteins are being developed for future HIV-1 vaccine trials in humans, with the goal of eliciting broadly active neutralizing antibodies (NAbs) that are active against a wide variety of circulating strains. In animal models, the present generation of native-like trimer immunogens, exemplified by the BG505 SOSIP.664 construct, induces narrow-specificity antibodies against the neutralization-resistant (tier-2), sequence-matched virus and more broadly active antibodies against sequence-divergent atypically neutralization-sensitive (tier-1) viruses. A concern in the trimer immunogen design field has been whether the latter off-target antibodies might interfere with the induction of the more desired responses to tier-2 epitopes. Here, we have inserted two glycans into the dominant site for tier-1 NAbs, the gp120 V3 region, to block the induction of off-target antibodies. We characterized the new trimers, tested them as immunogens in rabbits, and found that the blocking glycans eliminated the induction of tier-1 NAbs to V3-epitopes.

Project description:Human immunodeficiency virus type 1 (HIV-1) envelope (Env), a heterotrimer of gp120-gp41 subunits, mediates fusion of the viral and host cell membranes after interactions with the host receptor CD4 and a coreceptor. CD4 binding induces rearrangements in Env trimer, resulting in a CD4-induced (CD4i) open Env conformation. Structural studies of antibodies isolated from infected donors have defined antibody-Env interactions, with one class of antibodies specifically recognizing the CD4i open Env conformation. In this study, we characterized a group of monoclonal antibodies isolated from HIV-1 infected donors (V2i MAbs) that displayed characteristics of CD4i antibodies. Binding experiments demonstrated that the V2i MAbs preferentially recognize CD4-bound open Env trimers. Structural characterizations of V2i MAb-Env-CD4 trimer complexes using single-particle cryo-electron microscopy showed recognition by V2i MAbs using different angles of approach to the gp120 V1V2 domain and the β2/β3 strands on a CD4i open conformation Env with no direct interactions of the MAbs with CD4. We also characterized CG10, a CD4i antibody that was raised in mice immunized with a gp120-CD4 complex, bound to an Env trimer plus CD4. CG10 exhibited characteristics similar to those of the V2i antibodies, i.e., recognition of the open Env conformation, but showed direct contacts to both CD4 and gp120. Structural comparisons of these and previously characterized CD4i antibody interactions with Env provide a suggested mechanism for how these antibodies are elicited during HIV-1 infection. IMPORTANCE The RV144 HIV-1 clinical vaccination trial showed modest protection against viral infection. Antibody responses to the V1V2 region of HIV-1 Env gp120 were correlated inversely with the risk of infection, and data from three other clinical vaccine trials suggested a similar signal. In addition, antibodies targeting V1V2 have been correlated with protections from simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus (SHIV) infections in nonhuman primates. We structurally characterized V2i antibodies directed against V1V2 isolated from HIV-1 infected humans in complex with open Env trimers bound to the host receptor CD4. We also characterized a CD4i antibody that interacts with CD4 as well as the gp120 subunit of an open Env trimer. Our study suggests how V2i and CD4i antibodies were elicited during HIV-1 infection.

Dataset Information

Changes in Structure and Antigenicity of HIV-1 Env Trimers Resulting from Removal of a Conserved CD4 Binding Site-Proximal Glycan.

Publications

Changes in Structure and Antigenicity of HIV-1 Env Trimers Resulting from Removal of a Conserved CD4 Binding Site-Proximal Glycan.

Similar Datasets

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