Structural basis for scaffolding-mediated assembly and maturation of a dsDNA virus
Structural basis for scaffolding-mediated assembly and maturation of a dsDNA virus
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DOI：
10.1073/pnas.1015739108
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发表时间：
2011-01-25
影响因子：
11.1
通讯作者：
Chiu, Wah
中科院分区：
文献类型：
--
作者：
Chen, Dong-Hua;Baker, Matthew L.;Chiu, Wah
许多dsDNA病毒的形成始于原衣壳的组装，原衣壳含有支架蛋白和多亚基门户但缺乏DNA，其成熟为感染性病毒体。这个过程在双链DNA病毒如疱疹病毒和噬菌体中是保守的，是形成感染性病毒体的关键。在过去的几十年中，噬菌体P22一直是这项研究的模型系统。然而，如何启动衣壳组装，支架蛋白结合在哪里和如何在原衣壳的外壳蛋白，以及衣壳成熟后的构象变化仍然是难以捉摸的。在这里，我们报告C α骨干模型的P22前衣壳和感染性病毒体来自电子冷冻显微镜密度图确定在3.8-和4.0埃的分辨率，分别和第一个前衣壳结构在亚纳米分辨率不施加对称性。原衣壳结构显示支架蛋白通过其C-末端螺旋-环-螺旋基序与外壳蛋白的N末端（N臂）静电相互作用，以及10个支架蛋白和位于独特顶点的12倍门户之间的意想不到的相互作用。这表明支架蛋白在启动门户顶点的衣壳组装和在T = 7的二十面体晶格上传播其生长中起着关键作用。比较原衣壳和病毒体骨架模型揭示了协调和复杂的构象变化。这些结构的观察使我们能够提出一个更详细的分子机制的支架介导的衣壳装配启动，包括门户网站纳入，释放支架蛋白后，DNA包装，成熟成感染性病毒粒子。
Formation of many dsDNA viruses begins with the assembly of a procapsid, containing scaffolding proteins and a multisubunit portal but lacking DNA, which matures into an infectious virion. This process, conserved among dsDNA viruses such as herpes viruses and bacteriophages, is key to forming infectious virions. Bacteriophage P22 has served as a model system for this study in the past several decades. However, how capsid assembly is initiated, where and how scaffolding proteins bind to coat proteins in the procapsid, and the conformational changes upon capsid maturation still remain elusive. Here, we report C alpha backbone models for the P22 procapsid and infectious virion derived from electron cryomicroscopy density maps determined at 3.8- and 4.0-angstrom resolution, respectively, and the first procapsid structure at subnanometer resolution without imposing symmetry. The procapsid structures show the scaffolding protein interacting electrostatically with the N terminus (N arm) of the coat protein through its C-terminal helix-loop-helix motif, as well as unexpected interactions between 10 scaffolding proteins and the 12-fold portal located at a unique vertex. These suggest a critical role for the scaffolding proteins both in initiating the capsid assembly at the portal vertex and propagating its growth on a T = 7 icosahedral lattice. Comparison of the procapsid and the virion backbone models reveals coordinated and complex conformational changes. These structural observations allow us to propose a more detailed molecular mechanism for the scaffolding-mediated capsid assembly initiation including portal incorporation, release of scaffolding proteins upon DNA packaging, and maturation into infectious virions.