Banna virus (BAV) is the prototype Seadornavirus, a class of reoviruses for which there has been little structural study. Here, we report atomic cryo-EM structures of three states of BAV virions—surrounded by 120 spikes (full virions), 60 spikes (partial virions), or no spikes (cores). BAV cores are double-layered particles similar to the cores of other non-turreted reoviruses, except for an additional protein component in the outer capsid shell, VP10. VP10 was identified to be a cementing protein that plays a pivotal role in the assembly of BAV virions by directly interacting with VP2 (inner capsid), VP8 (outer capsid), and VP4 (spike). Viral spikes (VP4/VP9 heterohexamers) are situated on top of VP10 molecules in full or partial virions. Asymmetrical electrostatic interactions between VP10 monomers and VP4 trimers are disrupted by high pH treatment, which is thus a simple way to produce BAV cores. Low pH treatment of BAV virions removes only the flexible receptor binding protein VP9 and triggers significant conformational changes in the membrane penetration protein VP4. BAV virions adopt distinct spatial organization of their surface proteins compared with other well-studied reoviruses, suggesting that BAV may have a unique mechanism of penetration of cellular endomembranes.

版纳病毒 (BAV) 是海藻病毒的原型，是一类呼肠孤病毒，对其结构研究很少。在这里，我们报告了 BAV 病毒体三种状态的原子冷冻电镜结构——被 120 个尖峰（完整病毒体）、60 个尖峰（部分病毒体）或无尖峰（核心）包围。 BAV 核心是双层颗粒，与其他无塔呼肠孤病毒的核心相似，除了衣壳外壳中的额外蛋白质成分 VP10 之外。 VP10 被鉴定为一种胶结蛋白，通过直接与 VP2（内衣壳）、VP8（外衣壳）和 VP4（刺突）相互作用，在 BAV 病毒粒子的组装中发挥关键作用。病毒刺突（VP4/VP9 异六聚体）位于完整或部分病毒体中 VP10 分子的顶部。高 pH 处理会破坏 VP10 单体和 VP4 三聚体之间的不对称静电相互作用，因此这是生产 BAV 核心的简单方法。 BAV 病毒体的低 pH 处理仅去除柔性受体结合蛋白 VP9，并引发膜穿透蛋白 VP4 的显着构象变化。与其他经过充分研究的呼肠孤病毒相比，BAV 病毒体的表面蛋白采用独特的空间组织，这表明 BAV 可能具有独特的细胞内膜渗透机制。