Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 233 South 10th Street, Philadelphia, Pennsylvania 19107, USA.
Department of Biochemistry and Molecular Biology, Rutgers University, 683 Hoes lane, Piscataway, New Jersey 08854, USA.
Nat Commun. 2017 Jan 30;8:14310. doi: 10.1038/ncomms14310.
Tailed bacteriophages and herpesviruses assemble infectious particles via an empty precursor capsid (or 'procapsid') built by multiple copies of coat and scaffolding protein and by one dodecameric portal protein. Genome packaging triggers rearrangement of the coat protein and release of scaffolding protein, resulting in dramatic procapsid lattice expansion. Here, we provide structural evidence that the portal protein of the bacteriophage P22 exists in two distinct dodecameric conformations: an asymmetric assembly in the procapsid (PC-portal) that is competent for high affinity binding to the large terminase packaging protein, and a symmetric ring in the mature virion (MV-portal) that has negligible affinity for the packaging motor. Modelling studies indicate the structure of PC-portal is incompatible with DNA coaxially spooled around the portal vertex, suggesting that newly packaged DNA triggers the switch from PC- to MV-conformation. Thus, we propose the signal for termination of 'Headful Packaging' is a DNA-dependent symmetrization of portal protein.
长尾噬菌体和疱疹病毒通过由多个衣壳和支架蛋白以及一个十二聚体门户蛋白组成的空前体衣壳（或“原衣壳”）组装感染性颗粒。基因组包装会引发衣壳蛋白的重排和支架蛋白的释放，从而导致原衣壳晶格的剧烈扩张。在这里，我们提供了结构证据表明噬菌体 P22 的门户蛋白存在两种不同的十二聚体构象：原衣壳中的不对称组装（PC-门户），能够与大型末端酶包装蛋白高亲和力结合，以及成熟病毒粒子中的对称环（MV-门户），对包装马达几乎没有亲和力。建模研究表明，PC-门户的结构与围绕门户顶点同轴缠绕的 DNA 不兼容，这表明新包装的 DNA 触发了从 PC-到 MV-构象的转变。因此，我们提出终止“满载包装”的信号是门户蛋白的 DNA 依赖性对称化。
