Is the HIV-1 capsid modulated by a pentamer switch?

项目摘要/摘要 HIV-1 CA蛋白的12个五聚体具有塑造富勒烯锥体几何形状的关键功能 通过占据六角形衣壳晶格中的倾斜点或锐曲点， 从而允许组装的蛋白质外壳关闭。除了这种结构性作用，没有其他功能具有 之前被归因于CA五聚体。在这里，我们提出了HIV-1 CA的一个新的功能角色 五聚体。我们的前提是五聚体有两种截然不同的构象状态，一开始是一种 通过体外组装系统鉴定，第二种观察到的是平均五聚体构型 在病毒粒子中。已发表的研究和我们的初步数据表明，这两种五聚体形式有以下区别 两个配体结合位点的构型：一个与IP6结合，另一个与苯丙氨酸-甘氨酸(Fg)结合 含有宿主蛋白，如NUP153和其他核孔蛋白、CPSF6和SEC24C。我们建议， 不同的五聚体状态定义了一个分子开关，它调节衣壳进入后的结构。我们 进一步提出，我们的五聚体开关假说可以解释鲜为人知的衣壳性质和 功能，如作为衣壳稳定、脱壳和衣壳抑制的机制。在这 探索性R21项目，我们的主要目标是定义结构和生化特性 提出了五聚体开关，并验证了构象开关与配体偶联的关键预测 有约束力的。在两个特定的目标中，我们将应用蛋白质热分析和冷冻EM的现代实现， 从可溶性五聚体到组装的新型和建立的体外衣壳模型体系 衣壳状颗粒。如果得到证实，我们新颖而创新的五聚体开关假说将显著扩展 了解HIV-1衣壳功能的分子基础，有助于新型药物的开发 衣壳蛋白靶向抗病毒药物。

Project Summary/Abstract Twelve pentamers of the HIV-1 CA protein have the critical function of shaping the fullerene cone geometry of the mature capsid, by occupying declinations or sharp points of curvature in the hexagonal capsid lattice, and thereby allowing the assembling protein shell to close. Apart from this structural role, no other function has been previously ascribed to the CA pentamer. Here, we propose a novel functional role for the HIV-1 CA pentamer. Our premise is that there are two distinct conformational states of the pentamer, one initially identified through in vitro assembly systems and the second observed as the average pentamer configuration in virions. Published studies and our preliminary data indicate that the two pentamer forms are distinguished by the configurations of two ligand binding sites: one for IP6, and another for phenylalanine-glycine (FG) containing host proteins such as NUP153 and other nucleoporins, CPSF6 and SEC24C. We propose that the distinct pentamer states define a molecular switch that modulates the post-entry structure of the capsid. We further propose that our pentamer switch hypothesis can explain poorly-understood capsid properties and functions, such as mechanisms that underlie capsid stability, uncoating and capsid inhibition. In this exploratory R21 project, our major goals are to define the structural and biochemical properties of the proposed pentamer switch and test the key prediction that conformational switching is coupled to ligand binding. In two Specific Aims, we will apply modern implementations of protein thermal profiling and cryoEM, on novel and established in vitro capsid model systems that range from soluble pentamers to assembled capsid-like particles. If proven, our novel and innovative pentamer switch hypothesis would significantly expand understanding of the molecular basis of HIV-1 capsid function and could inform the development of novel capsid-targeted antivirals.