Structure of a clade C HIV-1 gp120 bound to CD4 and CD4-induced antibody reveals anti-CD4 polyreactivity

Division of Biology, California Institute of Technology, Pasadena, California, USA.
Nature Structural & Molecular Biology (Impact Factor: 13.31). 03/2010; 17(5):608-13. DOI: 10.1038/nsmb.1796
Source: PubMed


Strategies to combat HIV-1 require structural knowledge of envelope proteins from viruses in HIV-1 clade C, the most rapidly
spreading subtype in the world. We present a crystal structure containing a clade C gp120 envelope. The structure, a complex
between gp120, the host receptor CD4 and the CD4-induced antibody 21c, reveals that the 21c epitope involves contacts with
gp120, a nonself antigen, and with CD4, an autoantigen. Binding studies using wild-type and mutant CD4 show that 21c Fab binds
CD4 in the absence of gp120, and that binding of 21c to clade C and HIV-2 gp120s requires the crystallographically observed
21c-CD4 interaction. Additional binding data suggest a role for the gp120 V1V2 loop in creating a high-affinity, but slow-forming,
epitope for 21c after CD4 binds. These results contribute to a molecular understanding of CD4-induced antibodies and provide the
first visualization to our knowledge of a potentially autoreactive antibody Fab complexed with both self and nonself antigens.

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    • "Secreted gp120 was captured on Ni 2+ -NTA resin (GE Healthcare) and further purified using Superdex 200 16/60 size exclusion chromatography. Soluble CD4 domains 1 and 2 (sCD4) and sCD4 K75T were produced as described previously by Diskin et al. (2010). Briefly, the pACgp67b vector encoding 63-His-tagged sCD4 or sCD4 K75T (residues 1–186 of mature CD4) was used to make infectious baculovirus particles using BaculoGold (BD Bioscience ). "
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    ABSTRACT: Broadly neutralizing antibodies (bNAbs) to HIV-1 envelope glycoprotein (Env) can prevent infection in animal models. Characterized bNAb targets, although key to vaccine and therapeutic strategies, are currently limited. We defined a new site of vulnerability by solving structures of bNAb 8ANC195 complexed with monomeric gp120 by X-ray crystallography and trimeric Env by electron microscopy. The site includes portions of gp41 and N-linked glycans adjacent to the CD4-binding site on gp120, making 8ANC195 the first donor-derived anti-HIV-1 bNAb with an epitope spanning both Env subunits. Rather than penetrating the glycan shield by using a single variable-region CDR loop, 8ANC195 inserted its entire heavy-chain variable domain into a gap to form a large interface with gp120 glycans and regions of the gp120 inner domain not contacted by other bNAbs. By isolating additional 8ANC195 clonal variants, we identified a more potent variant, which may be valuable for therapeutic approaches using bNAb combinations with nonoverlapping epitopes.
    Full-text · Article · Apr 2014 · Cell Reports
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    • "According to a recent study, when the V1V2 domain and gp41 contacts are removed, the native monomer gp120 core adopts a conformation similar to a CD4 bound monomer conformation [61]. In Table 1, we have listed several properties of these reactive peptide regions based on known X-ray structures of liganded gp120 [48-53]. Trends in properties, such as secondary structure and solvent exposure, are consistent among different peptide within a reactive region. "
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    ABSTRACT: Neutralizing and non-neutralizing antibodies to linear epitopes on HIV-1 envelope glycoproteins have potential to mediate antiviral effector functions that could be beneficial to vaccine-induced protection. Here, plasma IgG responses were assessed in three HIV-1 gp120 vaccine efficacy trials (RV144, Vax003, Vax004) and in HIV-1-infected individuals by using arrays of overlapping peptides spanning the entire consensus gp160 of all major genetic subtypes and circulating recombinant forms (CRFs) of the virus. In RV144, where 31.2% efficacy against HIV-1 infection was seen, dominant responses targeted the C1, V2, V3 and C5 regions of gp120. An analysis of RV144 case-control samples showed that IgG to V2 CRF01_AE significantly inversely correlated with infection risk (OR= 0.54, p=0.0042), as did the response to other V2 subtypes (OR=0.60-0.63, p=0.016-0.025). The response to V3 CRF01_AE also inversely correlated with infection risk but only in vaccine recipients who had lower levels of other antibodies, especially Env-specific plasma IgA (OR=0.49, p=0.007) and neutralizing antibodies (OR=0.5, p=0.008). Responses to C1 and C5 showed no significant correlation with infection risk. In Vax003 and Vax004, where no significant protection was seen, serum IgG responses targeted the same epitopes as in RV144 with the exception of an additional C1 reactivity in Vax003 and infrequent V2 reactivity in Vax004. In HIV-1 infected subjects, dominant responses targeted the V3 and C5 regions of gp120, as well as the immunodominant domain, heptad repeat 1 (HR-1) and membrane proximal external region (MPER) of gp41. These results highlight the presence of several dominant linear B cell epitopes on the HIV-1 envelope glycoproteins. They also generate the hypothesis that IgG to linear epitopes in the V2 and V3 regions of gp120 are part of a complex interplay of immune responses that contributed to protection in RV144.
    Full-text · Article · Sep 2013 · PLoS ONE
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    • "The anti-influenza antibody 2D1 contains a three-codon insertion in a HV4-like region of FR3 which, while not directly involved in antigen recognition, causes a critical conformational shift in nearby CDRs that is required for antigen recognition (Krause et al., 2011). A unique example of HV4-like contribution to antigen recognition is the anti-HIV antibody 21c (Diskin et al., 2010). 21c binds to the HIV co-receptor binding pocket, which is only exposed following binding of CD4, the primary host receptor. "
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    ABSTRACT: V(D)J recombination and somatic hypermutation (SHM) are the primary mechanisms for diversification of the human antibody repertoire. These mechanisms allow for rapid humoral immune responses to a wide range of pathogenic challenges. V(D)J recombination efficiently generate a virtually limitless diversity through random recombination of variable (V), diversity (D), and joining (J) genes with diverse non-templated junctions between the selected gene segments. Following antigen stimulation, affinity maturation by SHM produces antibodies with refined specificity mediated by mutations typically focused in complementarity determining regions (CDRs), which form the bulk of the antigen recognition site. While V(D)J recombination and SHM are responsible for much of the diversity of the antibody repertoire, there are several secondary mechanisms that, while less frequent, make substantial contributions to antibody diversity including V(DD)J recombination (or D-D fusion), SHM-associated insertions and deletions, and affinity maturation and antigen contact by non-CDR regions of the antibody. In addition to enhanced diversity, these mechanisms allow the production of antibodies that are critical to response to a variety of viral and bacterial pathogens but that would be difficult to generate using only the primary mechanisms of diversification.
    Full-text · Article · Mar 2013 · Frontiers in Immunology
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