Antibody 2G12 uniquely neutralizes a broad range of HIV-1 isolates by binding the high-mannose glycans on the HIV-1 surface glycoprotein, gp120. Antigens that resemble these natural epitopes of 2G12 would be highly desirable components for an HIV-1 vaccine. However, host-produced (self)-carbohydrate motifs have been unsuccessful so far at eliciting 2G12-like antibodies that cross-react with gp120. Based on the surprising observation that 2G12 binds nonproteinaceous monosaccharide D-fructose with higher affinity than D-mannose, we show here that a designed set of nonself, synthetic monosaccharides are potent antigens. When introduced to the terminus of the D1 arm of protein glycans recognized by 2G12, their antigenicity is significantly enhanced. Logical variation of these unnatural sugars pinpointed key modifications, and the molecular basis of this increased antigenicity was elucidated using high-resolution crystallographic analyses. Virus-like particle protein conjugates containing such nonself glycans are bound more tightly by 2G12. As immunogens they elicit higher titers of antibodies than those immunogenic conjugates containing the self D1 glycan motif. These antibodies generated from nonself immunogens also cross-react with this self motif, which is found in the glycan shield, when it is presented in a range of different conjugates and glycans. However, these antibodies did not bind this glycan motif when present on gp120.
抗体2G12通过结合HIV-1表面糖蛋白gp120上的高甘露糖基糖来独特地中和广泛范围的HIV-1分离株。类似于2G12这些天然抗原表位的抗原将是HIV-1疫苗中非常理想的组分。然而,迄今为止,宿主产生的(自身)糖基图案未能引发与gp120交叉反应的2G12类抗体。基于令人惊讶的观察结果,即2G12比D-甘露糖更具亲和力地结合非蛋白单糖D-果糖,我们在这里展示了一组设计的非自身合成单糖是强效抗原。当引入到2G12识别的蛋白糖基的D1臂末端时,它们的抗原性显著增强。对这些非天然糖的逻辑变化指出了关键的修饰,通过高分辨率晶体学分析阐明了这种增加的抗原性的分子基础。含有这种非自身糖的病毒样颗粒蛋白共轭物被2G12更牢固地结合。作为免疫原,它们引发的抗体滴度比包含自身D1糖基图案的免疫原共轭物更高。从非自身免疫原引发的这些抗体也与在多种共轭物和糖基中呈现的这种自身图案交叉反应,然而,当它出现在gp120上时,这些抗体不结合这种糖基图案。