IAVI Neutralizing Antibody Center at TSRI, The Scripps Research Institute, La Jolla, CA 92037, USA.
J Virol. 2011 Aug;85(16):8217-26. doi: 10.1128/JVI.00756-11. Epub 2011 Jun 8.
On the prereceptor-engaged HIV-1 envelope glycoprotein (Env) spike, epitope access by the membrane-proximal external region (MPER)-directed broadly neutralizing antibodies 2F5 and 4E10 remains unresolved. Data on binding to cell surface Env and entry data using primary isolates suggest inaccessibility of the 2F5 and 4E10 epitopes on the viral spike prior to receptor engagement, but trimer gel shift analysis and slow kinetics of shedding induced by 2F5 and 4E10 indicate otherwise. Therefore, it remains unclear if the epitopes themselves are formed in their antibody-bound state (or at least sampled) prior to receptor/coreceptor engagement or if receptor interactions both expose and form the MPER epitopes, presumably in the putative prefusion transitional intermediate. Here, we performed antibody-virus "washout experiments" using both lab-adapted and a panel of clade B primary isolates to analyze MPER accessibility. The neutralization activity of 2F5 and 4E10 against lab-adapted viruses and sensitive and moderately resistant viruses was largely unaffected by relatively rapid antibody-virus washing, suggesting direct interaction with the "static" spike. However, for more neutralization-resistant viruses, the 2F5 and 4E10 antibodies could neutralize only under the "no antibody-virus wash" conditions, implying that the MPER epitopes were not accessible prior to receptor engagement. Accessibility in the washout conditions could be precisely predicted by the relative resistance to neutralization in a standard neutralization format. These data are consistent with a model in which the local MPER antibody epitope conformations may be sampled on the native spike but are occluded to antibody by local steric or distal quaternary constraints adopted by highly resistant HIV-1 isolates.
在与前受体结合的 HIV-1 包膜糖蛋白 (Env) 刺突上，膜近端外区 (MPER) 定向的广谱中和抗体 2F5 和 4E10 的表位可及性仍未得到解决。关于结合细胞表面 Env 和使用原发性分离物的进入数据表明，在受体结合之前，病毒刺突上的 2F5 和 4E10 表位不可及，但是三聚体凝胶迁移分析和 2F5 和 4E10 诱导的缓慢脱落动力学表明并非如此。因此，目前尚不清楚这些表位本身是否在受体/共受体结合之前就以其抗体结合状态（或至少被采样）形成，或者受体相互作用是否既暴露又形成 MPER 表位，推测在假定的预融合过渡中间体中形成。在这里，我们使用实验室适应的和一组 B 群原发性分离物进行了抗体-病毒“洗脱实验”，以分析 MPER 的可及性。2F5 和 4E10 对实验室适应的病毒以及敏感和中度耐药病毒的中和活性在相对快速的抗体-病毒洗涤后基本不受影响，这表明其与“静态”刺突的直接相互作用。然而，对于更具中和抗性的病毒，只有在“无抗体-病毒洗脱”条件下，2F5 和 4E10 抗体才能中和，这意味着在受体结合之前 MPER 表位不可及。在洗脱条件下的可及性可以通过在标准中和格式中对中和的相对抗性进行精确预测。这些数据与以下模型一致：局部 MPER 抗体表位构象可能在天然刺突上被采样，但由于高度耐药的 HIV-1 分离物采用的局部空间位阻或远程四级约束，而被抗体封闭。
