Division of Immunology, Department of Pathology, University of Cape Town, Cape Town, South Africa.
Program in Molecular Medicine, The Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.
J Virol. 2018 Jun 29;92(14). doi: 10.1128/JVI.02261-17. Print 2018 Jul 15.
Understanding the mechanisms used by HIV-1 to evade antibody neutralization may contribute to the design of a high-coverage vaccine. The tier 3 virus 253-11 is poorly neutralized by subtype-matched and subtype C sera, even compared to other tier 3 viruses, and is also recognized poorly by V3/glycan-targeting monoclonal antibodies (MAbs). We found that sequence polymorphisms in the V3 loop and N-linked glycosylation sites contribute only minimally to the high neutralization resistance of 253-11. Interestingly, the 253-11 membrane-proximal external region (MPER) is rarely recognized by sera in the context of the wild-type virus but is commonly recognized in the context of an HIV-2 chimera, suggesting steric or kinetic hindrance of binding to MPER in the native envelope (Env). Mutations in the 253-11 MPER, which were previously reported to increase the lifetime of the prefusion Env conformation, affected the resistance of 253-11 to antibodies targeting various epitopes on HIV-1 Env, presumably destabilizing its otherwise stable, closed trimer structure. To gain insight into the structure of 253-11, we constructed and crystallized a recombinant 253-11 SOSIP trimer. The resulting structure revealed that the heptad repeat helices in gp41 are drawn in close proximity to the trimer axis and that gp120 protomers also showed a relatively compact disposition around the trimer axis. These observations give substantial insight into the molecular features of an envelope spike from a tier 3 virus and into possible mechanisms that may contribute to its unusually high neutralization resistance. HIV-1 isolates that are highly resistant to broadly neutralizing antibodies could limit the efficacy of an antibody-based vaccine. We studied 253-11, which is highly resistant to commonly elicited neutralizing antibodies. To further understand its resistance, we made mutations that are known to delay fusion and thus increase the time that the virus spends in the open conformation following CD4 binding. Interestingly, we found that these mutations affect the 253-11 envelope (Env) spike before CD4 binding, presumably by destabilizing the trimer structure. To gain further information about the structure of the 253-11 Env trimer, we generated a recombinant 253-11 SOSIP trimer. The crystal structure of the SOSIP trimer revealed that the gp41 helices and the gp120 protomers were drawn in toward the center of the molecule compared to most solved HIV-1 Env structures. These observations provide insight into the distinct molecular features of a tier 3 envelope spike.
了解 HIV-1 逃避抗体中和的机制可能有助于设计高覆盖率的疫苗。第三层病毒 253-11 与亚型匹配和 C 型血清的中和作用很差，甚至与其他第三层病毒相比也是如此，并且也很难被 V3/聚糖靶向单克隆抗体（mAb）识别。我们发现，V3 环和 N 连接糖基化位点的序列多态性仅对 253-11 的高中和抗性有很小的贡献。有趣的是，253-11 膜近端外区域（MPER）在野生型病毒的情况下很少被血清识别，但在 HIV-2 嵌合体的情况下经常被识别，这表明在天然包膜（Env）中结合 MPER 存在空间或动力学障碍。先前报道的 253-11 MPER 中的突变可增加融合前 Env 构象的寿命，影响 253-11 对针对 HIV-1 Env 上各种表位的抗体的抗性，可能使它原本稳定的、封闭的三聚体结构不稳定。为了深入了解 253-11 的结构，我们构建并结晶了重组 253-11 SOSIP 三聚体。得到的结构表明，gp41 的七螺旋重复螺旋被拉近到三聚体轴附近，gp120 原聚体也围绕三聚体轴呈现相对紧凑的排布。这些观察结果深入了解了来自第三层病毒的包膜刺突的分子特征，并深入了解了可能导致其异常高中和抗性的可能机制。高度抵抗广泛中和抗体的 HIV-1 分离株可能会限制基于抗体的疫苗的功效。我们研究了对常见诱导的中和抗体高度抵抗的 253-11。为了进一步了解其抗性，我们制造了已知会延迟融合的突变，从而增加了病毒在结合 CD4 后处于开放构象的时间。有趣的是，我们发现这些突变在结合 CD4 之前影响 253-11 包膜（Env）刺突，可能是通过破坏三聚体结构。为了进一步了解 253-11 Env 三聚体的结构，我们生成了重组 253-11 SOSIP 三聚体。SOSIP 三聚体的晶体结构表明，与大多数已解决的 HIV-1 Env 结构相比，gp41 螺旋和 gp120 原聚体被拉向分子的中心。这些观察结果提供了对第三层包膜刺突的独特分子特征的深入了解。
