Structures of foot and mouth disease virus pentamers: Insight into capsid dissociation and unexpected pentamer reassociation.
Structures of foot and mouth disease virus pentamers: Insight into capsid dissociation and unexpected pentamer reassociation.
复制标题
DOI：
10.1371/journal.ppat.1006607
复制
发表时间：
2017-09
期刊：
影响因子：
6.7
通讯作者：
Stuart DI
中科院分区：
文献类型：
--
作者：
Malik N;Kotecha A;Gold S;Asfor A;Ren J;Huiskonen JT;Tuthill TJ;Fry EE;Stuart DI
口蹄疫病毒（FMDV）属于小核糖核酸病毒科Aphthovirus属，是一种小的、二十面体的、无包膜的单链RNA病毒。它是一种传染性很强的病原体，是动物和动物产品国际贸易的最大障碍之一。FMDV衣壳（在pH6.5以下是不稳定的）将它们的基因组从酸性隔间（如核内体）释放到宿主细胞中，并在此过程中解离成五聚体。虽然该家族的其他成员（肠病毒）已经被可视化地形成一个扩展的中间衣壳，其中有孔，内部衣壳蛋白（VP4）， n -末端（VP1）和RNA可以从孔中释放出来，但对于aphthovirus来说，没有任何这样的可视化状态，相反，衣壳似乎只是解离成五聚体。在这里，我们提出了分离的FMDV解离五聚体的8-Å分辨率结构，缺乏VP4。我们还发现这些五聚体重新结合成一个刚性的二十面对称组合，这使得它们的结构能够以更高的分辨率解决（5.2 Å）。在这个组合中，五聚体出人意料地“由内而外”结合，但它们暴露的疏水边缘仍然被掩埋。稳定的相互作用发生在VP2的HI环与其对称相关的伙伴之间的二十面体3重轴上，VP3的BC环和EF环与VP2 β b链和CD环之间的2重轴上。与成熟病毒相比，向游离五聚体外围相对广泛但微妙的结构重排提供了对FMDV解离机制和抗原性显着差异的见解。这是FMDV解离五聚体的第一个结构，实际上是任何小核糖核酸病毒的第一个结构。我们还首次展示了由VP1、vp2和vp3组成的五聚体组装而成的小核糖核酸病毒颗粒的可视化。规则组装而不是随机聚集的形成使我们能够使用低温电子显微镜以相对高的分辨率解决结构。总的来说，与完整病毒粒子中的结构相比，被拆解的五聚体几乎没有大规模的构象变化，这表明成熟的病毒五聚体本质上是一个稳定的终点。然而，VP3的小旋转取消了通常的五聚体界面，再加上VP4的缺乏，导致这些五聚体亚基的异常内向外结合，而不是正确的衣壳组装。这种被拆解的五聚体构象的改变改变了抗原表面，如果破坏了天然颗粒的完整性，可能是疫苗失去效力的部分原因。
Foot-and-mouth disease virus (FMDV) belongs to the Aphthovirus genus of the Picornaviridae, a family of small, icosahedral, non-enveloped, single-stranded RNA viruses. It is a highly infectious pathogen and is one of the biggest hindrances to the international trade of animals and animal products. FMDV capsids (which are unstable below pH6.5) release their genome into the host cell from an acidic compartment, such as that of an endosome, and in the process dissociate into pentamers. Whilst other members of the family (enteroviruses) have been visualized to form an expanded intermediate capsid with holes from which inner capsid proteins (VP4), N-termini (VP1) and RNA can be released, there has been no visualization of any such state for an aphthovirus, instead the capsid appears to simply dissociate into pentamers. Here we present the 8-Å resolution structure of isolated dissociated pentamers of FMDV, lacking VP4. We also found these pentamers to re-associate into a rigid, icosahedrally symmetric assembly, which enabled their structure to be solved at higher resolution (5.2 Å). In this assembly, the pentamers unexpectedly associate ‘inside out’, but still with their exposed hydrophobic edges buried. Stabilizing interactions occur between the HI loop of VP2 and its symmetry related partners at the icosahedral 3-fold axes, and between the BC and EF loops of VP3 with the VP2 βB-strand and the CD loop at the 2-fold axes. A relatively extensive but subtle structural rearrangement towards the periphery of the dissociated pentamer compared to that in the mature virus provides insight into the mechanism of dissociation of FMDV and the marked difference in antigenicity. This is the first structure of dissociated pentamers for FMDV, and indeed for any picornavirus. We also present the first visualization of a picornavirus particle assembled from pentamers comprising VP1, 2 and 3. The formation of regular assemblies rather than random aggregates has enabled us to solve the structure to relatively high resolution using cryo-electron microscopy. Overall there are remarkably few large-scale conformational changes in the dis-assembled pentamer from its structure in the intact virion, suggesting that the mature virus pentamer is essentially a stable endpoint. However, a small rotation in VP3 abrogates the usual pentamer interface and together with the lack of VP4 drives the abnormal inside-out association of these pentameric subunits, rather than the correct capsid assembly. This change in conformation of the dis-assembled pentamer changes the antigenic surface and presumably underlies, in part, the loss of efficacy of vaccines if native particle integrity is destroyed.