Thuman-Commike P A, Greene B, Malinski J A, King J, Chiu W
Department of Computational and Applied Mathematics, W. M. Keck Center for Computational Biology, Rice University, Houston, Texas 77005-1892, USA.
Biophys J. 1998 Jan;74(1):559-68. doi: 10.1016/S0006-3495(98)77814-2.
Assembly of bacteriophage P22 procapsids requires the participation of approximately 300 molecules of scaffolding protein in addition to the 420 coat protein subunits. In the absence of the scaffolding, the P22 coat protein can assemble both wild-type-size and smaller size closed capsids. Both sizes of procapsid assembled in the absence of the scaffolding protein have been studied by electron cryomicroscopy. These structural studies show that the larger capsids have T = 7 icosahedral lattices and appear the same as wild-type procapsids. The smaller capsids possess T = 4 icosahedral symmetry. The two procapsids consist of very similar penton and hexon clusters, except for an increased curvature present in the T = 4 hexon. In particular, the pronounced skewing of the hexons is conserved in both sizes of capsid. The T = 7 procapsid has a local non-icosahedral twofold axis in the center of the hexon and thus contains four unique quasi-equivalent coat protein conformations that are the same as those in the T = 4 procapsid. Models of how the scaffolding protein may direct these four coat subunit types into a T = 7 rather than a T = 4 procapsid are presented.
噬菌体P22前衣壳的组装除了需要420个衣壳蛋白亚基外，还需要大约300个分子的支架蛋白参与。在没有支架蛋白的情况下，P22衣壳蛋白可以组装成野生型大小和较小尺寸的封闭衣壳。通过电子冷冻显微镜对在没有支架蛋白的情况下组装的两种大小的前衣壳进行了研究。这些结构研究表明，较大的衣壳具有T = 7的二十面体晶格，外观与野生型前衣壳相同。较小的衣壳具有T = 4的二十面体对称性。这两种前衣壳由非常相似的五聚体和六聚体簇组成，只是T = 4的六聚体中存在更大的曲率。特别是，六聚体明显的扭曲在两种大小的衣壳中都是保守的。T = 7的前衣壳在六聚体中心有一个局部非二十面体的二重轴，因此包含四种独特的准等效衣壳蛋白构象，与T = 4的前衣壳中的构象相同。本文提出了支架蛋白如何将这四种衣壳亚基类型引导到T = 7而不是T = 4的前衣壳中的模型。
