The hallmark of a virus is its capsid, which harbors the viral genome and is formed from protein subunits, which assemble following precise geometric rules. dsRNA viruses use an unusual protein multiplicity (120 copies) to form their closed capsids. We have determined the atomic structure of the capsid protein (P1) from the dsRNA cystovirus Φ8. In the crystal P1 forms pentamers, very similar in shape to facets of empty procapsids, suggesting an unexpected assembly pathway that proceeds via a pentameric intermediate. Unlike the elongated proteins used by dsRNA mammalian reoviruses, P1 has a compact trapezoid-like shape and a distinct arrangement in the shell, with two near-identical conformers in nonequivalent structural environments. Nevertheless, structural similarity with the analogous protein from the mammalian viruses suggests a common ancestor. The unusual shape of the molecule may facilitate dramatic capsid expansion during phage maturation, allowing P1 to switch interaction interfaces to provide capsid plasticity.

译文

病毒的标志是它的衣壳,它藏有病毒基因组,由蛋白质亚基形成,这些亚基按照精确的几何规则组装。dsRNA病毒使用一种不寻常的蛋白质多样性 (120个拷贝) 来形成它们的封闭衣壳类。我们已经确定了dsRNA囊病毒 Φ8的衣壳蛋白 (P1) 的原子结构。在晶体中,P1形成五聚体,其形状与空的前五胞体的小面非常相似,这表明通过五聚体中间体进行的意外组装途径。与dsRNA哺乳动物reoviruses使用的细长蛋白不同,P1具有紧凑的梯形形状和在壳中的独特排列,在非等效结构环境中具有两个几乎相同的构象体。尽管如此,与哺乳动物病毒类似蛋白的结构相似,表明有共同的祖先。分子的异常形状可能会在噬菌体成熟过程中促进衣壳的急剧膨胀,从而允许P1切换相互作用界面以提供衣壳可塑性。

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