Trus Benes L, Newcomb William W, Cheng Naiqian, Cardone Giovanni, Marekov Lyuben, Homa Fred L, Brown Jay C, Steven Alasdair C
Laboratory of Structural Biology Research, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Mol Cell. 2007 May 25;26(4):479-89. doi: 10.1016/j.molcel.2007.04.010.
UL25 and UL17 are two essential minor capsid proteins of HSV-1, implicated in DNA packaging and capsid maturation. We used cryo-electron microscopy to examine their binding to capsids, whose architecture observes T = 16 icosahedral geometry. C-capsids (mature DNA-filled capsids) have an elongated two-domain molecule present at a unique, vertex-adjacent site that is not seen at other quasiequivalent sites or on unfilled capsids. Using SDS-PAGE and mass spectrometry to analyze wild-type capsids, UL25 null capsids, and denaturant-extracted capsids, we conclude that (1) the C-capsid-specific component is a heterodimer of UL25 and UL17, and (2) capsids have additional populations of UL25 and UL17 that are invisible in reconstructions because of sparsity and/or disorder. We infer that binding of the ordered population reflects structural changes induced on the outer surface as pressure builds up inside the capsid during DNA packaging. Its binding may signal that the C-capsid is ready to exit the nucleus.
UL25和UL17是单纯疱疹病毒1型（HSV-1）的两种重要的小衣壳蛋白，与DNA包装和衣壳成熟有关。我们使用冷冻电子显微镜来检查它们与衣壳的结合情况，衣壳结构遵循T = 16二十面体几何形状。C型衣壳（充满成熟DNA的衣壳）在一个独特的、与顶点相邻的位点存在一个细长的双结构域分子，在其他准等效位点或未填充的衣壳上未见此结构。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）和质谱分析野生型衣壳、UL25缺失衣壳和变性剂提取的衣壳，我们得出以下结论：（1）C型衣壳特异性成分是UL25和UL17的异二聚体；（2）衣壳中存在额外的UL25和UL17群体，由于稀疏性和/或无序性，在重建中不可见。我们推断，有序群体的结合反映了在DNA包装过程中衣壳内部压力增加时在外表面诱导的结构变化。其结合可能表明C型衣壳已准备好离开细胞核。
