Thuman-Commike P A, Greene B, Jakana J, Prasad B V, King J, Prevelige P E, Chiu W
Program in Structural & Computational Biology & Molecular Biophysics, Baylor College of Medicine, Houston, TX 77030, USA.
J Mol Biol. 1996 Jul 5;260(1):85-98. doi: 10.1006/jmbi.1996.0383.
The procapsids of bacterial viruses are the products of the polymerization of coat and scaffolding subunits, as well as the precursors in DNA packaging. Electron cryo-microscopy has been used to study the three-dimensional structures of bacteriophage P22 procapsids containing wild-type and mutant scaffolding proteins. The scaffolding mutant structure has been resolved to 19 A resolution and agrees with the 22 A resolution wild-type procapsid reconstruction. Both procapsid reconstructions contain an outer icosahedral coat protein shell and an inner scaffolding protein core. The outer core protein forms a T = 7 icosahedral lattice with distinctive channels present at the centers of the pentons and hexons. In addition, the hexons display a prominent skew. Computational isolation of the skewed hexon shows the presence of a local 2-fold axis that reduces the number of unique conformations in the asymmetric unit to four at this resolution. We have classified the four unique subunits into three distinct classes, based upon the shape of the upper domain and the presence of a channel leading to the inner coat protein surface. In addition, at the inner surface of the coat protein, finger-like regions that extend towards the scaffolding protein core are present in two of the subunits. The finger-like regions suggest the presence of an ordered interaction between the inner coat protein and the scaffolding protein. However, an icosahedral scaffolding protein shell is not formed, and the innermost scaffolding protein core does not pack with icosahedral symmetry.
细菌病毒的原衣壳是衣壳亚基和支架亚基聚合的产物，也是DNA包装的前体。电子冷冻显微镜已被用于研究含有野生型和突变型支架蛋白的噬菌体P22原衣壳的三维结构。支架突变体结构已解析到19埃分辨率，与22埃分辨率的野生型原衣壳重建结果一致。两种原衣壳重建都包含一个二十面体的外壳蛋白壳和一个内部支架蛋白核心。外部核心蛋白形成一个T = 7的二十面体晶格，在五聚体和六聚体的中心有独特的通道。此外，六聚体呈现出明显的倾斜。对倾斜六聚体的计算分离显示存在一个局部2次轴，在该分辨率下，不对称单元中独特构象的数量减少到四个。根据上结构域的形状和通向内部衣壳蛋白表面的通道的存在，我们将这四个独特的亚基分为三个不同的类别。此外，在衣壳蛋白的内表面，两个亚基中存在朝向支架蛋白核心延伸的指状区域。这些指状区域表明内部衣壳蛋白和支架蛋白之间存在有序的相互作用。然而，没有形成二十面体的支架蛋白壳，最内层的支架蛋白核心也没有以二十面体对称方式堆积。
