Powell Rebecca L R, Totrov Maxim, Itri Vincenza, Liu Xiaomei, Fox Alisa, Zolla-Pazner Susan
Department of Medicine, Division of Infectious Diseases, Icahn School of Medicine at Mount Sinai, New York, New York, USA
Molsoft, LLC, San Diego, California, USA.
J Virol. 2017 Aug 10;91(17). doi: 10.1128/JVI.00410-17. Print 2017 Sep 1.
We recently showed that mutations in the HIV-1 envelope (Env) destabilize the V3 loop, rendering neutralization-resistant viruses sensitive to V3-directed monoclonal antibodies (MAbs). Here, we investigated the propagation of this effect on other Env epitopes, with special emphasis on V2 loop exposure. Wild-type JR-FL and 19 mutant JR-FL pseudoviruses were tested for neutralization sensitivity to 21 MAbs specific for epitopes in V2, the CD4 binding site (CD4bs), and the CD4-induced (CD4i) region. Certain glycan mutants, mutations in the gp120 hydrophobic core, and mutations in residues involved in intraprotomer interactions exposed epitopes in the V2i region (which overlies the α4β7 integrin binding site) and the V3 crown, suggesting general destabilization of the distal region of the trimer apex. In contrast, other glycan mutants, mutations affecting interprotomer interactions, and mutations affecting the CD4bs exposed V3 but not V2i epitopes. These data indicate for the first time that V3 can move independently of V2, with V3 pivoting out from its "tucked" position in the trimer while apparently leaving the V2 apex intact. Notably, none of the mutations exposed V2 epitopes without also exposing V3, suggesting that movement of V2 releases V3. Most mutations increased sensitivity to CD4bs-directed MAbs without exposure of the CD4i epitope, implying these mutations facilitate the trimers' maintenance of an intermediate energy state between open and closed conformations. Taken together, these data indicate that several transient Env epitopes can be rendered more accessible to antibodies (Abs) via specific mutations, and this may facilitate the design of V1V2-targeting immunogens. Many epitopes of the HIV envelope (Env) spike are relatively inaccessible to antibodies (Abs) compared to their exposure in the open Env conformation induced by receptor binding. However, the reduced infection rate that resulted from the vaccine used in the RV144 HIV-1 vaccine trial was correlated with the elicitation of V2- and V3-directed antibodies. Previously, we identified various mechanisms responsible for destabilizing the V3 loop; here, we determined, via mutation of numerous Env residues, which of these elements maintain the V1V2 loop in an inaccessible state and which expose V1V2 and/or V3 epitopes. Notably, our data indicate that V3 can move independently of V2, but none of the mutations studied expose V2 epitopes without also exposing V3. Additionally, V1V2 can be rendered more accessible to Abs via specific mutations, facilitating the development of engineered V2 immunogens.
我们最近发现，HIV-1包膜（Env）中的突变会使V3环不稳定，从而使中和抗性病毒对V3导向的单克隆抗体（MAb）敏感。在此，我们研究了这种效应在其他Env表位上的传播情况，特别关注V2环的暴露情况。对野生型JR-FL和19种突变型JR-FL假病毒进行了测试，以检测它们对21种针对V2、CD4结合位点（CD4bs）和CD4诱导（CD4i）区域表位的MAb的中和敏感性。某些聚糖突变体、gp120疏水核心中的突变以及原聚体内相互作用所涉及残基的突变，会暴露V2i区域（覆盖α4β7整合素结合位点）和V3冠中的表位，这表明三聚体顶端远端区域普遍不稳定。相比之下，其他聚糖突变体、影响原聚体间相互作用的突变以及影响CD4bs的突变会暴露V3，但不会暴露V2i表位。这些数据首次表明，V3可以独立于V2移动，V3从三聚体中其“缩进”位置向外旋转，而V2顶端显然保持完整。值得注意的是，没有一种突变在不暴露V3的情况下暴露V2表位，这表明V2的移动会释放V3。大多数突变增加了对CD4bs导向MAb的敏感性，而未暴露CD4i表位，这意味着这些突变有助于三聚体维持开放和封闭构象之间的中间能量状态。综上所述，这些数据表明，通过特定突变可使几个瞬时Env表位更容易被抗体（Ab）识别，这可能有助于设计靶向V1V2的免疫原。与受体结合诱导的开放Env构象中相比，HIV包膜（Env）刺突的许多表位相对难以被抗体（Ab）识别。然而，RV144 HIV-1疫苗试验中使用的疫苗导致的感染率降低与V2和V3导向抗体的诱导有关。此前，我们确定了导致V3环不稳定的各种机制；在此，我们通过对众多Env残基进行突变，确定了哪些元件使V1V2环处于难以接近的状态，哪些元件暴露了V1V2和/或V3表位。值得注意的是，我们的数据表明V3可以独立于V2移动，但所研究的突变中没有一种在不暴露V3的情况下暴露V2表位。此外，通过特定突变可使V1V2更容易被Ab识别，这有助于开发工程化V2免疫原。
