Department of Medicinal Chemistry, University of Washington School of Pharmacy, H172 Health Sciences Building, Campus Box 357610, Seattle, WA 98195-7610, USA.
J Mol Biol. 2010 Sep 3;401(5):813-30. doi: 10.1016/j.jmb.2010.06.060. Epub 2010 Jul 8.
Viral capsids are robust structures designed to protect the genome from environmental insults and deliver it to the host cell. The developmental pathway for complex double-stranded DNA viruses is generally conserved in the prokaryotic and eukaryotic groups and includes a genome packaging step where viral DNA is inserted into a pre-formed procapsid shell. The procapsids self-assemble from monomeric precursors to afford a mature icosahedron that contains a single "portal" structure at a unique vertex; the portal serves as the hole through which DNA enters the procapsid during particle assembly and exits during infection. Bacteriophage lambda has served as an ideal model system to study the development of the large double-stranded DNA viruses. Within this context, the lambda procapsid assembly pathway has been reported to be uniquely complex involving protein cross-linking and proteolytic maturation events. In this work, we identify and characterize the protease responsible for lambda procapsid maturation and present a structural model for a procapsid-bound protease dimer. The procapsid protease possesses autoproteolytic activity, it is required for degradation of the internal "scaffold" protein required for procapsid self-assembly, and it is responsible for proteolysis of the portal complex. Our data demonstrate that these proteolytic maturation events are not required for procapsid assembly or for DNA packaging into the structure, but that proteolysis is essential to late steps in particle assembly and/or in subsequent infection of a host cell. The data suggest that the lambda-like proteases and the herpesvirus-like proteases define two distinct viral protease folds that exhibit little sequence or structural homology but that provide identical functions in virus development. The data further indicate that procapsid assembly and maturation are strongly conserved in the prokaryotic and eukaryotic virus groups.
病毒衣壳是坚固的结构，旨在保护基因组免受环境侵害，并将其递送至宿主细胞。复杂双链 DNA 病毒的发育途径在原核生物和真核生物群体中普遍保守，包括基因组包装步骤，其中病毒 DNA 插入预先形成的原衣壳壳中。原衣壳自组装单体前体以提供成熟的二十面体，其中在独特顶点处存在单一“门户”结构；门户作为 DNA 在颗粒组装过程中进入原衣壳并在感染过程中退出的孔。噬菌体 λ 已成为研究大型双链 DNA 病毒发育的理想模型系统。在这种情况下，已报道 λ 原衣壳组装途径独特复杂，涉及蛋白质交联和蛋白水解成熟事件。在这项工作中，我们鉴定并表征了负责 λ 原衣壳成熟的蛋白酶，并提出了原衣壳结合蛋白酶二聚体的结构模型。原衣壳蛋白酶具有自蛋白水解活性，它是原衣壳自组装所需的内部“支架”蛋白降解所必需的，并且负责门户复合物的蛋白水解。我们的数据表明，这些蛋白水解成熟事件不是原衣壳组装或 DNA 包装到结构所必需的，但蛋白水解对于颗粒组装的后期步骤和/或随后的宿主细胞感染是必需的。数据表明，λ 样蛋白酶和疱疹病毒样蛋白酶定义了两种不同的病毒蛋白酶折叠，它们具有很少的序列或结构同源性，但在病毒发育中提供相同的功能。数据还表明，原衣壳组装和成熟在原核生物和真核生物病毒群体中得到了强烈的保守。
