Department of Microbiology, Tokushima University Graduate School of Biomedical Sciences, Tokushima, Tokushima, Japan.
Laboratory of Viral Genomics, Pathogen Genomics Center, National Institute of Infectious Diseases, Musashimurayama, Tokyo, Japan.
J Virol. 2021 Jun 10;95(13):e0217720. doi: 10.1128/JVI.02177-20.
Molecular interactions of the variable envelope gp120 subunit of HIV-1 with two cellular receptors are the first step of viral infection, thereby playing pivotal roles in determining viral infectivity and cell tropism. However, the underlying regulatory mechanisms for interactions under gp120 spontaneous variations largely remain unknown. Here, we show an allosteric mechanism in which a single gp120 mutation remotely controls the ternary interactions between gp120 and its receptors for the switch of viral cell tropism. Virological analyses showed that a G310R substitution at the tip of the gp120 V3 loop selectively abolished the viral replication ability in human cells, despite evoking enhancement of viral replication in macaque cells. Molecular dynamics (MD) simulations predicted that the G310R substitution at a site away from the CD4 interaction site selectively impeded the binding ability of gp120 to human CD4. Consistently, virions with the G310R substitution exhibited a reduced binding ability to human lymphocyte cells. Furthermore, the G310R substitution influenced the gp120-CCR5 interaction in a CCR5-type dependent manner as assessed by MD simulations and an infectivity assay using exogenously expressed CCR5s. Interestingly, an I198M mutation in human CCR5 restored the infectivity of the G310R virus in human cells. Finally, MD simulation predicted amino acid interplays that physically connect the V3 loop and gp120 elements for the CD4 and CCR5 interactions. Collectively, these results suggest that the V3 loop tip is a -allosteric regulator that remotely controls intra- and intermolecular interactions of HIV-1 gp120 for balancing ternary interactions with CD4 and CCR5. Understanding the molecular bases for viral entry into cells will lead to the elucidation of one of the major viral survival strategies, and thus to the development of new effective antiviral measures. As shown recently, HIV-1 is highly mutable and adaptable in growth-restrictive cells, such as those of macaque origin. HIV-1 initiates its infection by sequential interactions of Env-gp120 with two cell surface receptors, CD4 and CCR5. A recent epoch-making structural study has disclosed that CD4-induced conformation of gp120 is stabilized upon binding of CCR5 to the CD4-gp120 complex, whereas the biological significance of this remains totally unknown. Here, from a series of mutations found in our extensive studies, we identified a single-amino acid adaptive mutation at the V3 loop tip of Env-gp120 critical for its interaction with both CD4 and CCR5 in a host cell species-specific way. This remarkable finding could certainly provoke and accelerate studies to precisely clarify the HIV-1 entry mechanism.
HIV-1 的可变包膜 gp120 亚单位与两种细胞受体的分子相互作用是病毒感染的第一步，因此在决定病毒感染力和细胞嗜性方面起着关键作用。然而，gp120 自发变异下相互作用的潜在调节机制在很大程度上仍然未知。在这里，我们展示了一种变构机制，其中 gp120 的单个突变远程控制 gp120 与其受体之间的三元相互作用，从而改变病毒的细胞嗜性。病毒学分析表明，gp120 V3 环尖端的 G310R 取代选择性地消除了病毒在人类细胞中的复制能力，尽管在猕猴细胞中引发了病毒复制的增强。分子动力学 (MD) 模拟预测，远离 CD4 结合位点的 G310R 取代位点选择性地阻碍了 gp120 与人 CD4 的结合能力。一致地，带有 G310R 取代的病毒粒子显示出与人淋巴细胞结合能力降低。此外，通过 MD 模拟和使用外源性表达的 CCR5 进行的感染性测定，G310R 取代影响了 gp120-CCR5 相互作用，这种影响依赖于 CCR5 型。有趣的是，人类 CCR5 中的 I198M 突变恢复了 G310R 病毒在人类细胞中的感染性。最后，MD 模拟预测了连接 V3 环和 gp120 元素的用于 CD4 和 CCR5 相互作用的氨基酸相互作用。总的来说，这些结果表明，V3 环尖端是一种变构调节剂，可远程控制 HIV-1 gp120 的分子内和分子间相互作用，以平衡与 CD4 和 CCR5 的三元相互作用。 了解病毒进入细胞的分子基础将导致阐明病毒的主要生存策略之一，从而开发新的有效抗病毒措施。如最近所示，HIV-1 在生长受限细胞（如猕猴来源的细胞）中高度易变和适应。HIV-1 通过 Env-gp120 与两种细胞表面受体 CD4 和 CCR5 的顺序相互作用启动感染。最近的一项开创性结构研究揭示了 CD4 诱导的 gp120 构象在 CCR5 与 CD4-gp120 复合物结合时得到稳定，而其生物学意义尚完全未知。在这里，我们从广泛研究中发现的一系列突变中，鉴定出一个位于 Env-gp120 V3 环尖端的单个氨基酸适应性突变，该突变对其与宿主细胞物种特异性的 CD4 和 CCR5 的相互作用至关重要。这一显著发现肯定会引发并加速研究，以精确阐明 HIV-1 进入机制。
