Garcea R L, Salunke D M, Caspar D L
Nature. 1987;329(6134):86-7. doi: 10.1038/329086a0.
Nonequivalent bonding of identical protein subunits occurs in the polyomavirus capsid were identical pentameric capsomeres occupy both hexavalent and pentavalent positions in the icosahedral surface lattice. The polyomavirus major capsid protein VP1, purified after expression of the recombinant gene in Escherichia coli, has been isolated as capsomeres that self-assemble into capsid-like structures in vitro. The ability to switch bonding specificity in different symmetry environments therefore must be intrinsic to the VP1 molecule. In vitro self-assembly provides an assay for VP1 mutations affecting capsomere and capsid formation. We report here that a directed mutation in the VP1 expression vector, leading to a protein truncated at the carboxy terminus, results in a mutant VP1 that forms capsomeres, but not capsids, in the in vitro assembly assay. The carboxy terminus of VP1 therefore appears to be involved in the specific bonding responsible for the non-equivalent association of capsomeres.
在多瘤病毒衣壳中，相同蛋白质亚基存在不等价结合，相同的五聚体壳粒在二十面体表面晶格中占据六价和五价位置。在大肠杆菌中表达重组基因后纯化得到的多瘤病毒主要衣壳蛋白VP1，已作为壳粒分离出来，这些壳粒在体外能自组装成类似衣壳的结构。因此，在不同对称环境中切换结合特异性的能力必定是VP1分子所固有的。体外自组装为影响壳粒和衣壳形成的VP1突变提供了一种检测方法。我们在此报告，VP1表达载体中的一个定向突变导致蛋白质在羧基末端被截断，产生了一种突变VP1，在体外组装试验中它能形成壳粒，但不能形成衣壳。因此，VP1的羧基末端似乎参与了负责壳粒不等价缔合的特异性结合。
