HIV-1 gp120的构象控制机制

During the process of HIV-1 virus entry into the host cells, the viral envelope glycoprotein gp120 undergoes a series of conformational rearrangements that are proposed to be linked to the virus invasion and immune evasion. However, how many conformational states can the full-length gp120 assume in its isolated form or in the viral spike environment? Do the factors that cause conformational changes and their underlying mechanisms of control differ between the isolated gp120 and spike gp120? These two key questions have remained elusive. This project will construct the loop-truncated and full-length structural models for both the isolated and functional viral spike gp120, either in the unliganded or in the CD4-bound states. These models will be subjected to extensive molecular dynamics simulations followed by calculations and analyses of free energy landscapes of these protein-solvent systems. Our aims are to (i) cluster a variety of potential gp120 conformational states that co-exist in equilibrium and to analyze the conformational transition ability between them; (ii) analyze the effects of the V1/V2, V3 variable loops and gp41 interaction on the stability of distinct gp120 conformational states and on the transition between them. The expected results are that we would obtain the information about the conformational diversity of the full-length gp120 molecule in the functional viral spike environment, and would find out the structural factors capable of maintaining the conformational equilibrium or causing conformational transition between these equilibrium states. The results of this project will complement the data derived from the X-ray crystallographic and physicochemical studies, thus facilitating the understanding of the conformational control mechanism of gp120 and the mechanism of the immune evasion of HIV-1.

HIV-1病毒在进入宿主细胞过程中,其膜糖蛋白gp120的一系列构象重排与病毒的入侵以及免疫逃避密切相关。然而，全长gp120分子在孤立和病毒轴环境中究竟采取哪些构象状态？引起其构象变化的因素及其控制机制是否相同等关键问题尚不清楚。本项目拟在前期工作的基础上，构建不包含环区的、以及全长的、处于受体结合前后两种构象状态的gp120结构模型和病毒轴模型，通过分子动力学模拟和自由能全景图谱计算，归类、分析溶液环境中孤立gp120以及病毒轴中gp120的各种平衡构象状态及其之间的转换能力；分析V1/V2、V3环以及gp41相互作用对gp120构象稳定及转换的影响。本研究将获得病毒轴环境中全长gp120分子的构象多样性信息，并探明维持gp120构象平衡以及导致gp120构象变化的结构因素。研究结果将弥补晶体学和物理化学研究的不足，有助于揭示gp120的构象控制机制和HIV-1的免疫逃避机制。

HIV-1病毒包被三聚体（Env trimer）中gp120分子的构象变化在病毒侵染和免疫逃逸中扮演着关键角色。因此，研究gp120的结构动力学、分子运动、以及热力学和能力学性质，查明维持gp120构象平衡以及导致gp120构象转换的结构因素，这对深入理解HIV-1的侵染机制和免疫逃避机理具有重要意义。本项目在构建不包含环区的、以及接近全长的、处于unliganded和CD4-bound状态gp120结构模型的基础上，通过分子动力学模拟、元动力学模拟、主成分分析（或本质动力学分析）、以及自由能图谱重构等手段，深入研究了CD4结合前后不同状态gp120的动力学、分子运动及其构象分布和转换能力。主要发现为：（1）对于不包含V1/V2区域的gp120核心结构，CD4-bound态为其自由能最低的稳定基态，而对于包含V1/V2区域的全长gp120，unliganded状态为其自由能最低的稳定基态；（2）CD4的结合会导致V1/V2与V3环的分离以及二者的剧烈波动，最终导致CD4-complexed gp120构象柔性和构象多样性的增加；（3）gp120核心和全长结构的运动模式均表现为全局或局部结构区域的涡轮样旋转或平移，而V1/V2区域相对于V3环和桥片层组分的运动方向则与gp120不同状态间的转化密切相关；（4）CD4结合空腔的呼吸和扭转运动可能与CD4分子的结合、定位以及脱落有关；（5）在没有CD4诱导的情况下，抗体中和敏感毒株gp120比抗体中和抗性毒株gp120更倾向于采取CD4-bound状态。综合以上结果，我们认为，V1/V2区域是维持gp120不同构象状态平衡分布关键结构因素，V1/V2的运动能力及其动力学行为决定了gp120构象状态间的平衡分布、转换以及gp120的全局动力学行为；在病毒包被三聚体中，gp120亚单位通过V1/V2和V3环之间的四级非共价相互作用将gp120维持在unliganded状态的同时还隐藏了绝大部分抗体中和表位，CD4结合或高V1/V2运动能力会导致V1/V2的位置重排，使得gp120转变到CD4-bound态，最终导致了辅助受体结合位点和抗体表位的形成和暴露。