Booy F P, Trus B L, Newcomb W W, Brown J C, Conway J F, Steven A C
Laboratory of Structural Biology, National Institute of Arthritis, Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892.
Proc Natl Acad Sci U S A. 1994 Jun 7;91(12):5652-6. doi: 10.1073/pnas.91.12.5652.
Macromolecular complexes that consist of homopolymeric protein frameworks with additional proteins attached at strategic sites for a variety of structural and functional purposes are widespread in subcellular biology. One such complex is the capsid of herpes simplex virus type 1 whose basic framework consists of 960 copies of the viral protein, VP5 (149 kDa), arranged in an icosahedrally symmetric shell. This shell also contains major amounts of three other proteins, including VP26 (12 kDa), a small protein that is approximately equimolar with VP5 and accounts for approximately 6% of the capsid mass. With a view to inferring the role of VP26 in capsid assembly, we have localized it by quantitative difference imaging based on three-dimensional reconstructions calculated from cryo-electron micrographs. Purified capsids from which VP26 had been removed in vitro by treatment with guanidine hydrochloride were compared with preparations of the same depleted capsids to which purified VP26 had been rebound and with native (undepleted) capsids. The resulting three-dimensional density maps indicate that six VP26 subunits are distributed symmetrically around the outer tip of each hexon protrusion on VP26-containing capsids. Because VP26 may be readily dissociated from and reattached to the capsid, it does not appear to contribute significantly to structural stabilization. Rather, its exposed location suggests that VP26 may be involved in linking the capsid to the surrounding tegument and envelope at a later stage of viral assembly.
由均聚物蛋白质框架组成的大分子复合物，在其特定位置附着有其他蛋白质以实现各种结构和功能目的，这种复合物在亚细胞生物学中广泛存在。一种这样的复合物是单纯疱疹病毒1型的衣壳，其基本框架由960个病毒蛋白VP5（149 kDa）拷贝组成，排列成二十面体对称外壳。这个外壳还包含大量的其他三种蛋白质，包括VP26（12 kDa），一种与VP5摩尔数大致相等且约占衣壳质量6%的小蛋白质。为了推断VP26在衣壳组装中的作用，我们基于从冷冻电子显微照片计算得到的三维重建，通过定量差异成像对其进行了定位。将通过用盐酸胍处理在体外去除了VP26的纯化衣壳，与相同的去除了VP26的衣壳制剂以及重新结合了纯化VP26的制剂和天然（未去除）衣壳进行比较。所得的三维密度图表明，六个VP26亚基对称分布在含VP26衣壳上每个六邻体突起的外尖端周围。由于VP26很容易从衣壳上解离并重新附着，它似乎对结构稳定没有显著贡献。相反，其暴露的位置表明VP26可能在病毒组装的后期参与将衣壳与周围的被膜和包膜连接起来。
