Spencer J V, Newcomb W W, Thomsen D R, Homa F L, Brown J C
Department of Microbiology and Cancer Center, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
J Virol. 1998 May;72(5):3944-51. doi: 10.1128/JVI.72.5.3944-3951.1998.
The herpes simplex virus type 1 (HSV-1) capsid is a T=16 icosahedral shell that forms in the nuclei of infected cells. Capsid assembly also occurs in vitro in reaction mixtures created from insect cell extracts containing recombinant baculovirus-expressed HSV-1 capsid proteins. During capsid formation, the major capsid protein, VP5, and the scaffolding protein, pre-VP22a, condense to form structures that are extended into procapsids by addition of the triplex proteins, VP19C and VP23. We investigated whether triplex proteins bind to the major capsid-scaffold protein complexes as separate polypeptides or as preformed triplexes. Assembly products from reactions lacking one triplex protein were immunoprecipitated and examined for the presence of the other. The results showed that neither triplex protein bound unless both were present, suggesting that interaction between VP19C and VP23 is required before either protein can participate in the assembly process. Sucrose density gradient analysis was employed to determine the sedimentation coefficients of VP19C, VP23, and VP19C-VP23 complexes. The results showed that the two proteins formed a complex with a sedimentation coefficient of 7.2S, a value that is consistent with formation of a VP19C-VP23(2) heterotrimer. Furthermore, VP23 was observed to have a sedimentation coefficient of 4.9S, suggesting that this protein exists as a dimer in solution. Deletion analysis of VP19C revealed two domains that may be required for attachment of the triplex to major capsid-scaffold protein complexes; none of the deletions disrupted interaction of VP19C with VP23. We propose that preformed triplexes (VP19C-VP23(2) heterotrimers) interact with major capsid-scaffold protein complexes during assembly of the HSV-1 capsid.
单纯疱疹病毒1型（HSV-1）衣壳是一种T=16的二十面体外壳，在受感染细胞的细胞核中形成。衣壳组装也可在体外由含有重组杆状病毒表达的HSV-1衣壳蛋白的昆虫细胞提取物制成的反应混合物中发生。在衣壳形成过程中，主要衣壳蛋白VP5和支架蛋白前VP22a凝聚形成结构，通过添加三聚体蛋白VP19C和VP23扩展为原衣壳。我们研究了三聚体蛋白是作为单独的多肽还是作为预先形成的三聚体与主要衣壳-支架蛋白复合物结合。对缺乏一种三聚体蛋白的反应的组装产物进行免疫沉淀，并检查另一种蛋白的存在情况。结果表明，除非两种三聚体蛋白都存在，否则它们都不会结合，这表明VP19C和VP23之间的相互作用是两种蛋白参与组装过程之前所必需的。采用蔗糖密度梯度分析来确定VP19C、VP23和VP19C-VP23复合物的沉降系数。结果表明，这两种蛋白形成了一种沉降系数为7.2S的复合物，该值与VP19C-VP23(2)异源三聚体的形成一致。此外，观察到VP23的沉降系数为4.9S，这表明该蛋白在溶液中以二聚体形式存在。VP19C的缺失分析揭示了两个可能是三聚体与主要衣壳-支架蛋白复合物结合所必需的结构域；没有一个缺失破坏VP19C与VP23的相互作用。我们提出，在HSV-1衣壳组装过程中，预先形成的三聚体（VP19C-VP23(2)异源三聚体）与主要衣壳-支架蛋白复合物相互作用。
