Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo, 679-5148, Japan.
Plant Pathology Laboratory, Faculty of Agriculture, Iwate University, Ueda 3-chome 18-8, Morioka, Iwate, 020-8550, Japan.
Commun Biol. 2020 Sep 4;3(1):488. doi: 10.1038/s42003-020-01217-4.
Picorna-like plant viruses are non-enveloped RNA spherical viruses of ~30 nm. Part of the survival of these viruses depends on their capsid being stable enough to harbour the viral genome and yet malleable enough to allow its release. However, molecular mechanisms remain obscure. Here, we report a structure of a picorna-like plant virus, apple latent spherical virus, at 2.87 Å resolution by single-particle cryo-electron microscopy (cryo-EM) with a cold-field emission beam. The cryo-EM map reveals a unique structure composed of three capsid proteins Vp25, Vp20, and Vp24. Strikingly Vp25 has a long N-terminal extension, which substantially stabilises the capsid frame of Vp25 and Vp20 subunits. Cryo-EM images also resolve RNA genome leaking from a pentameric protrusion of Vp24 subunits. The structures and observations suggest that genome release occurs through occasional opening of the Vp24 subunits, possibly suppressed to a low frequency by the rigid frame of the other subunits.
类微小 RNA 植物病毒是无包膜的 RNA 球形病毒，直径约 30nm。这些病毒的部分存活取决于其衣壳足够稳定以容纳病毒基因组，同时又具有足够的柔韧性以允许其释放。然而，分子机制仍不清楚。在这里，我们通过使用冷场发射束的单颗粒冷冻电镜（cryo-EM）以 2.87Å 的分辨率报告了一种类微小 RNA 植物病毒，即苹果潜隐球形病毒的结构。冷冻电镜图谱揭示了一种由三个衣壳蛋白 Vp25、Vp20 和 Vp24 组成的独特结构。引人注目的是，Vp25 具有长的 N 端延伸，这大大稳定了 Vp25 和 Vp20 亚基的衣壳框架。冷冻电镜图像还解析了从 Vp24 亚基的五聚体突出部泄漏的 RNA 基因组。这些结构和观察结果表明，基因组的释放是通过 Vp24 亚基的偶尔打开发生的，这种打开可能被其他亚基的刚性框架抑制在低频率。
