The importance of the V1/V2 domain as a target in HIV-1 vaccines has been shown by demonstrations that epitopes to potently neutralizing antibodies are localized to this region, that binding between a site in V1/V2 and 4 7 receptors facilitates infection of primary CD4-positive T cells, and that the presence of antibodies binding to a fusion glycoprotein expressing the isolated V1/V2 domain correlates with protection in the RV144 vaccine trial. The native V1/V2 domain of the CaseA2 clade B Env sequence was expressed by fusion to the C-terminus of a 273 amino acid fragment of the MuLV gp70 domain. This fusion glycoprotein was characterized by SDS-PAGE after radioimmunoprecipitation with a panel of mAbs directed against V1/V2-specific epitopes, and by MALDI-TOF analysis of immunologically fractionated forms. SDS-PAGE analysis of this protein after deglycosylation under non-reducing conditions revealed the presence of a closely migrating doublet, and the two forms reacted differentially with a panel of V1/V2-specific antibodies and various polyclonal sera. Mass-spec analysis of the immunologically fractionated forms suggested that these consisted of different disulfide-linked conformers. These studies demonstrate a conformational heterogeneity in the V1/V2 domain that is due to alternative disulfide bonding patterns. These conformations profoundly affect the immunoreactivity of this region, and will presumably influence their immunogenicity as well. This structural heterogeneity may impact the immunogenicity of standard Env-based immunogens, and methods for resolving this heterogeneity may improve the efficacy of induction of relevant antibodies to this region by HIV Env vaccines.
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