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: 11.63). 03/2010; 17(5):608-13. DOI: 10.1038/nsmb.1796
Source: PubMed

ABSTRACT 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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    • "Although our study does not provide data on the physical structure of the V1V2 domain per se, it offers new information on the quaternary organization of the V1V2 loop in the context of the Env trimer. The results of our analysis fit well with currently available structural data of gp120 and proposed models of the quaternary geometry of gp120 subunits within the trimeric spike (Kwong et al., 1998, 2000; Chen et al., 2005; Huang et al., 2005; Zanetti et al., 2006; Zhu et al., 2006; Liu et al., 2008a; Chen et al., 2009; Diskin et al., 2010; Finzi et al., 2010; Kong et al., 2010; Pancera et al., 2010; White et al., 2010; Xiang et al., 2010; Hu et al., 2011). A potential interaction of the V1V2 domain with the adjacent monomer's V3 loop has been considered for long (Kwong et al., 2000; Chen et al., 2005) but until to date could not be confirmed in the absence of the definition of a high-resolution trimer structure. "
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    • "Lipid polyreactivity of gp41 nAbs is required for neutralization (Alam et al., 2009). An antibody binding to the CD4-inducible CCR5 binding site on gp120 has been found that also uses adjacent bound CD4 as a part of the CD4i epitope (Diskin et al., 2010). Because of the low number of Env trimer spikes on the HIV-1 virion, the likelihood of bivalent antibody-virion binding in the absence of antibody polyreactivity is small (Klein and Bjorkman, 2010). "
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