Mayo Keith, McDermott Jason, Barklis Eric
Vollum Institute and Department of Microbiology, Oregon Health Sciences University, Portland 97201-3098, USA.
Virology. 2002 Jun 20;298(1):30-8. doi: 10.1006/viro.2002.1452.
To help elucidate the mechanisms by which retrovirus structural proteins associate to form virus particles, we have examined membrane-bound assemblies of Moloney murine leukemia virus (M-MuLV) capsid (CA) proteins. Electron microscopy and image reconstruction techniques showed that CA dimers appear to function as organizational subunits of the cage-like, membrane-bound protein arrays. However, new three-dimensional (3D) data also were consistent with hexagonal (p6) assembly models. The p6 3D reconstructions of membrane-bound M-MuLV CA proteins gave unit cells of a = b = 80.3 A, c = 110 A, gamma = 120 degrees, in which six dimer units formed a cage lattice. Neighbor cage hole-to-hole distances were 45 A, while distances between hexagonal cage holes corresponded to unit cell lengths (80.3 A). The hexagonal model predicts two types of cage holes (trimer and hexamer holes), uses symmetric head-to-head dimer building blocks, and permits the introduction of lattice curvature by conversion of hexamer to pentamer units. The M-MuLV CA lattice is similar to those formed in helical tubes by HIV CA in that hexamer units surround cage holes of 25-30 A, but differs in that M-MuLV hexamer units appear to be CA dimers, whereas HIV CA units appear to be monomers. These results suggest that while general assembly principles apply to different retroviruses, clear assembly distinctions exist between these virus types.
为了帮助阐明逆转录病毒结构蛋白缔合形成病毒颗粒的机制，我们研究了莫洛尼鼠白血病病毒（M-MuLV）衣壳（CA）蛋白的膜结合聚集体。电子显微镜和图像重建技术表明，CA二聚体似乎作为笼状膜结合蛋白阵列的组织亚基发挥作用。然而，新的三维（3D）数据也与六边形（p6）组装模型一致。膜结合的M-MuLV CA蛋白的p6 3D重建给出了晶胞参数a = b = 80.3 Å，c = 110 Å，γ = 120°，其中六个二聚体单元形成一个笼状晶格。相邻笼孔之间的孔间距为45 Å，而六边形笼孔之间的距离对应于晶胞长度（80.3 Å）。六边形模型预测了两种类型的笼孔（三聚体孔和六聚体孔），使用对称的头对头二聚体构建块，并允许通过将六聚体单元转化为五聚体单元来引入晶格曲率。M-MuLV CA晶格与HIV CA在螺旋管中形成的晶格相似，即六聚体单元围绕25 - 30 Å的笼孔，但不同之处在于M-MuLV六聚体单元似乎是CA二聚体，而HIV CA单元似乎是单体。这些结果表明，虽然一般的组装原则适用于不同的逆转录病毒，但这些病毒类型之间存在明显的组装差异。
