Structure of the immature retroviral capsid at 8 Å resolution by cryo-electron microscopy
Structure of the immature retroviral capsid at 8 Å resolution by cryo-electron microscopy
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DOI：
10.1038/nature11169
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发表时间：
2012-07-19
期刊：
影响因子：
64.8
通讯作者：
Briggs, John A. G.
中科院分区：
文献类型：
--
作者：
Bharat, Tanmay A. M.;Davey, Norman E.;Briggs, John A. G.
逆转录病毒如HIV-1的组装是由其主要结构蛋白Gag的寡聚化驱动的。Gag是一种多结构域多蛋白，包括三个保守的折叠结构域：MA（基质）、CA（衣壳）和NC（核衣壳）（1）。感染性病毒粒子的组装分为两个阶段（2）。在第一阶段中，Gag寡聚化成六聚体蛋白质晶格导致形成不完整的大致球形的蛋白质壳，该蛋白质壳通过感染细胞的质膜出芽以释放有包膜的未成熟病毒颗粒。在第二阶段，病毒蛋白酶切割Gag导致颗粒内部重排，将非感染性未成熟病毒颗粒转化为成熟感染性病毒体。不成熟的Gag壳是组装过程中的关键中间体，并且是抗逆转录病毒药物抑制病毒组装和破坏病毒成熟的潜在靶点（3）。然而，关于未成熟的加格壳的详细结构信息以前没有。由于这个原因，目前还不清楚什么样的蛋白质构象和界面介导结构域之间的相互作用，因此逆转录病毒颗粒的组装，以及什么样的结构转变与逆转录病毒成熟有关。在这里，我们解决了梅森-辉瑞猴病毒的未成熟逆转录病毒Gag外壳的结构，结合冷冻电子显微镜和断层扫描。8埃的分辨率结构允许在未成熟的逆转录病毒中推导出CA的伪原子模型，其定义了介导逆转录病毒组装的蛋白质界面。我们发现，一个不成熟的逆转录病毒到其成熟的感染形式的过渡涉及显着的旋转和翻译的CA域，CA的氨基末端和羧基末端结构域在组装的不成熟和成熟的六聚体晶格的作用交换，CA的相互作用，稳定的不成熟和成熟的病毒几乎是完全不同的。
The assembly of retroviruses such as HIV-1 is driven by oligomerization of their major structural protein, Gag. Gag is a multidomain polyprotein including three conserved folded domains: MA (matrix), CA (capsid) and NC (nucleocapsid)(1). Assembly of an infectious virion proceeds in two stages(2). In the first stage, Gag oligomerization into a hexameric protein lattice leads to the formation of an incomplete, roughly spherical protein shell that buds through the plasma membrane of the infected cell to release an enveloped immature virus particle. In the second stage, cleavage of Gag by the viral protease leads to rearrangement of the particle interior, converting the non-infectious immature virus particle into a mature infectious virion. The immature Gag shell acts as the pivotal intermediate in assembly and is a potential target for anti-retroviral drugs both in inhibiting virus assembly and in disrupting virus maturation(3). However, detailed structural information on the immature Gag shell has not previously been available. For this reason it is unclear what protein conformations and interfaces mediate the interactions between domains and therefore the assembly of retrovirus particles, and what structural transitions are associated with retrovirus maturation. Here we solve the structure of the immature retroviral Gag shell from Mason-Pfizer monkey virus by combining cryo-electron microscopy and tomography. The 8-angstrom resolution structure permits the derivation of a pseudo-atomic model of CA in the immature retrovirus, which defines the protein interfaces mediating retrovirus assembly. We show that transition of an immature retrovirus into its mature infectious form involves marked rotations and translations of CA domains, that the roles of the amino-terminal and carboxy-terminal domains of CA in assembling the immature and mature hexameric lattices are exchanged, and that the CA interactions that stabilize the immature and mature viruses are almost completely distinct.