Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA.
J Virol. 2011 Oct;85(19):9974-83. doi: 10.1128/JVI.05013-11. Epub 2011 Jul 20.
During cell entry, native poliovirus (160S) converts to a cell-entry intermediate (135S) particle, resulting in the externalization of capsid proteins VP4 and the amino terminus of VP1 (residues 1 to 53). Externalization of these entities is followed by release of the RNA genome (uncoating), leaving an empty (80S) particle. The antigen-binding fragment (Fab) of a monospecific peptide 1 (P1) antibody, which was raised against a peptide corresponding to amino-terminal residues 24 to 40 of VP1, was utilized to track the location of the amino terminus of VP1 in the 135S and 80S states of poliovirus particles via cryogenic electron microscopy (cryo-EM) and three-dimensional image reconstruction. On 135S, P1 Fabs bind to a prominent feature on the external surface known as the "propeller tip." In contrast, our initial 80S-P1 reconstruction showed P1 Fabs also binding to a second site, at least 50 Å distant, at the icosahedral 2-fold axes. Further analysis showed that the overall population of 80S-P1 particles consisted of three kinds of capsids: those with P1 Fabs bound only at the propeller tips, P1 Fabs bound only at the 2-fold axes, or P1 Fabs simultaneously bound at both positions. Our results indicate that, in 80S particles, a significant fraction of VP1 can deviate from icosahedral symmetry. Hence, this portion of VP1 does not change conformation synchronously when switching from the 135S state. These conclusions are compatible with previous observations of multiple conformations of the 80S state and suggest that movement of the amino terminus of VP1 has a role in uncoating. Similar deviations from icosahedral symmetry may be biologically significant during other viral transitions.
在细胞进入过程中，天然脊髓灰质炎病毒（160S）转化为细胞进入中间物（135S）颗粒，导致衣壳蛋白 VP4 和 VP1 氨基末端（残基 1 至 53）的外化。这些实体的外化之后是 RNA 基因组的释放（脱壳），留下空的（80S）颗粒。针对 VP1 氨基末端残基 24 至 40 的肽 1（P1）肽的单特异性肽抗体的抗原结合片段（Fab）被用于通过低温电子显微镜（cryo-EM）和三维图像重建来跟踪 135S 和 80S 状态的脊髓灰质炎病毒颗粒中 VP1 氨基末端的位置。在 135S 上，P1 Fab 结合到外部表面上称为“推进器尖端”的明显特征上。相比之下，我们最初的 80S-P1 重建显示 P1 Fab 也结合到第二个位点，至少 50 Å 远，在二十面体 2 倍轴上。进一步的分析表明，80S-P1 颗粒的总体群体由三种衣壳组成：那些仅在推进器尖端结合 P1 Fab 的衣壳，仅在 2 倍轴上结合 P1 Fab 的衣壳，或同时在两个位置结合 P1 Fab 的衣壳。我们的结果表明，在 80S 颗粒中，VP1 的很大一部分可以偏离二十面体对称性。因此，当从 135S 状态切换时，VP1 的这一部分不会同步改变构象。这些结论与之前观察到的 80S 状态的多种构象一致，并表明 VP1 氨基末端的移动在脱壳中起作用。在其他病毒转变过程中，类似的偏离二十面体对称性可能具有生物学意义。
