Biochemistry of HIV-1 Budding

描述(申请人提供)：以前的研究发现，HIV-1利用TSG101/ESCRT-I和MVB囊泡形成的细胞途径从细胞到芽。我们的研究还概述了MVB途径的各个组成部分，它们的成对相互作用，以及一系列MVB蛋白和复合体的三维结构，包括：TSG101 UEV/PTAP复合体，Alix YPXL结合域，Vps4 MIT和ATPase结构域，以及具有TSG101 UEV，Npl4 NZF和EAP45胶域的泛素复合体。然而，我们还不了解大多数基本途径功能的基本机制，包括调节、蛋白质分类、膜变形和膜分裂。我们现在建议对三种不同的MVB复合体进行生化、机制和结构研究，这三种复合体在HIV-1萌芽中发挥作用。目标1的研究将集中在人ESGRT-I的生物化学上。ESCRT-I直接与HIV-1 Gag的PTAP晚期结构域结合，促进病毒释放。我们最近开发了表达和纯化重组ESCRT-I复合体的系统，并发现了以前未描述的ESCRT-I亚单位的第四个家族。我们现在将在这些观察的基础上定义ESCRT-I的准确组成，测试ESCRT-I的激活和调节模型，并表征一系列ESCRT-I结合蛋白。Aim 2的研究将集中在Alix/AIP1蛋白的结构和功能上，该蛋白直接与YPXL晚期结构域结合，促进病毒萌发。我们已经建立了分析Alix在HIV-1释放中的作用的系统，并确定了Alix中心YPXL结合区的晶体结构。我们现在将绘制YPXL结合位点图，测试晚期结构域引起构象变化从而激活Alix的假设，并表征Alix结合伙伴在病毒萌发中的作用。目标3的研究将集中于了解Vps4 ATPase如何与ESCRT-III晶格相互作用，并从膜上释放组装的MVB机械。VPS4A和VPS4B是MVB途径中仅有的已知酶，它们的ATPase活性是释放HIV-1和许多其他病毒所必需的。我们现在建议确定Vps4是如何识别ESCRT-III底物的，并测试Vps4作为一种特殊的伴侣蛋白发挥作用的模型，该伴侣利用ATP水解的能量来展开ESCRT-III亚基，将它们从膜上释放出来，并可能还驱动囊泡/病毒的释放。

DESCRIPTION (provided by applicant): Previous research led to the discovery that HIV-1 utilizes TSG101/ESCRT-I and the cellular pathway of MVB vesicle formation to bud from cells. Our studies also provided a general overview of the individual components of the MVB pathway, their pairwise interactions, and three dimensional structures of a series of MVB proteins and complexes, including: the TSG101 UEV/PTAP complex, the ALIX YPXL binding domain, VPS4 MIT and ATPase domains, and ubiquitin complexes with the TSG101 UEV, Npl4 NZF, and EAP45 GLUE domains. Nevertheless, we do not yet understand the basic mechanisms that underlie most essential pathway functions including regulation, protein sorting, membrane deformation, and membrane fission. We now propose biochemical, mechanistic, and structural studies of three different MVB complexes that function in HIV-1 budding. Studies in Aim 1 will focus on the biochemistry of human ESGRT-I. ESCRT-I binds directly to the PTAP late domain of HIV-1 Gag and facilitates virus release. We have recently developed systems for expressing and purifying recombinant ESCRT-I complexes and discovered a fourth family of previously uncharacterized ESCRT-I subunits. We will now build on these observations to define the precise composition of ESCRT-I, test models for ESCRT-I activation and regulation, and characterize a series of ESCRT-I binding proteins. Studies in Aim 2 will focus on the structure and function of the ALIX/AIP1 protein, which binds directly to YPXL late domains and faciliates virus budding. We have developed systems for analyzing the role of ALIX in HIV-1 release and determined the crystal structure of the central YPXL binding region of ALIX. We will now map the YPXL binding site, test the hypothesis that late domains induce conformational changes that activate ALIX, and characerize the roles of ALIX binding partners in virus budding. Studies in Aim 3 will focus on understanding how the VPS4 ATPases interact with the ESCRT-III lattice and release the assembled MVB machinery from the membrane. VPS4A and VPS4B are the only known enzymes in the MVB pathway, and their ATPase activity is required for release of HIV-1 and many other viruses. We now propose to determine how VPS4 recognizes ESCRT-III substrates and to test the model that VPS4 functions as a specialized chaperone that uses the energy of ATP hydrolysis to unfold ESCRT-III subunits, release them from the membrane, and possibly also drive vesicle/virus release.