Plevka Pavel, Tars Kaspars, Liljas Lars
Department of Cell and Molecular Biology, Uppsala University, SE-751 24 Uppsala, Sweden.
Protein Sci. 2008 Oct;17(10):1731-9. doi: 10.1110/ps.036905.108. Epub 2008 Jul 28.
A covalent dimer of the bacteriophage MS2 coat protein was created by performing genetic fusion of two copies of the gene while removing the stop codon of the first gene. The dimer was crystallized in the cubic F432 space group. The organization of the asymmetric unit together with the F432 symmetry results in an arrangement of subunits that corresponds to T = 3 octahedral particles. The octahedral particles are probably artifacts created by the particular crystal packing. When it is not crystallized in the F cubic crystal form, the coat protein dimer appears to assemble into T = 3 icosahedral particles indistinguishable from the wild-type particles. To form an octahedral particle with closed surface, the dimer subunits interact at sharper angles than in the icosahedral arrangement. The fold of the covalent dimer is almost identical to the wild-type dimer with differences located in loops and in the covalent linker region. The main differences in the subunit packing between the octahedral and icosahedral arrangements are located close to the fourfold and fivefold symmetry axes where different sets of loops mediate the contacts. The volume of the wild-type virions is 7 times bigger than that of the octahedral particles.
通过对噬菌体MS2外壳蛋白基因的两个拷贝进行基因融合,同时去除第一个基因的终止密码子,构建了该蛋白的共价二聚体。该二聚体在立方F432空间群中结晶。不对称单元的结构与F432对称性共同导致了亚基的排列,形成了对应于T = 3八面体颗粒的结构。这些八面体颗粒可能是由特定晶体堆积产生的假象。当外壳蛋白二聚体不以F立方晶体形式结晶时,它似乎会组装成与野生型颗粒无法区分的T = 3二十面体颗粒。为了形成具有封闭表面的八面体颗粒,二聚体亚基之间的相互作用角度比二十面体排列中的角度更尖锐。共价二聚体的折叠与野生型二聚体几乎相同,差异位于环区和共价连接区域。八面体和二十面体排列之间亚基堆积的主要差异位于四重和五重对称轴附近,不同的环介导了这些接触。野生型病毒粒子的体积比八面体颗粒大7倍。