Chen Jinhuan, Zhang Chao, Zhou Yu, Zhang Xiang, Shen Chaoyun, Ye Xiaohua, Jiang Wen, Huang Zhong, Cong Yao
National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, China.
Shanghai Science Research Center, Chinese Academy of Sciences, Shanghai, China.
J Virol. 2018 Jan 2;92(2). doi: 10.1128/JVI.01257-17. Print 2018 Jan 15.
Coxsackievirus A6 (CVA6) has recently emerged as one of the predominant causative agents of hand, foot, and mouth disease (HFMD). The structure of the CVA6 mature viral particle has not been solved thus far. Our previous work shows that recombinant virus-like particles (VLPs) of CVA6 represent a promising CVA6 vaccine candidate. Here, we report the first cryo-electron microscopy (cryo-EM) structure of the CVA6 VLP at 3.0-Å resolution. The CVA6 VLP exhibits the characteristic features of enteroviruses but presents an open channel at the 2-fold axis and an empty, collapsed VP1 pocket, which is broadly similar to the structures of the enterovirus 71 (EV71) VLP and coxsackievirus A16 (CVA16) 135S expanded particle, indicating that the CVA6 VLP is in an expanded conformation. Structural comparisons reveal that two common salt bridges within protomers are maintained in the CVA6 VLP and other viruses of the genus, implying that these salt bridges may play a critical role in enteroviral protomer assembly. However, there are apparent structural differences among the CVA6 VLP, EV71 VLP, and CVA16 135S particle in the surface-exposed loops and C termini of subunit proteins, which are often antigenic sites for enteroviruses. By immunological assays, we identified two CVA6-specific linear B-cell epitopes (designated P42 and P59) located at the GH loop and the C-terminal region of VP1, respectively, in agreement with the structure-based prediction of antigenic sites. Our findings elucidate the structural basis and important antigenic sites of the CVA6 VLP as a strong vaccine candidate and also provide insight into enteroviral protomer assembly. Coxsackievirus A6 (CVA6) is becoming one of the major pathogens causing hand, foot, and mouth disease (HFMD), leading to significant morbidity and mortality in children and adults. However, no vaccine is currently available to prevent CVA6 infection. Our previous work shows that recombinant virus-like particles (VLPs) of CVA6 are a promising CVA6 vaccine candidate. Here, we present a 3.0-Å structure of the CVA6 VLP determined by cryo-electron microscopy. The overall architecture of the CVA6 VLP is similar to those of the expanded structures of enterovirus 71 (EV71) and coxsackievirus A16 (CVA16), but careful structural comparisons reveal significant differences in the surface-exposed loops and C termini of each capsid protein of these particles. In addition, we identified two CVA6-specific linear B-cell epitopes and mapped them to the GH loop and the C-terminal region of VP1, respectively. Collectively, our findings provide a structural basis and important antigenic information for CVA6 VLP vaccine development.
柯萨奇病毒A6（CVA6）最近已成为手足口病（HFMD）的主要致病因子之一。迄今为止，CVA6成熟病毒颗粒的结构尚未得到解析。我们之前的研究表明，CVA6重组病毒样颗粒（VLP）是一种很有前景的CVA6疫苗候选物。在此，我们报告了CVA6 VLP在3.0 Å分辨率下的首个冷冻电子显微镜（cryo-EM）结构。CVA6 VLP呈现出肠道病毒的特征性结构，但在二重对称轴处有一个开放通道，且VP1口袋为空的、塌陷的状态，这与肠道病毒71型（EV71）VLP和柯萨奇病毒A16（CVA16）135S扩展颗粒的结构大致相似，表明CVA6 VLP处于扩展构象。结构比较显示，CVA6 VLP和该属其他病毒的原体中存在两个常见的盐桥，这意味着这些盐桥可能在肠道病毒原体组装中起关键作用。然而，CVA6 VLP、EV71 VLP和CVA16 135S颗粒在亚基蛋白的表面暴露环和C末端存在明显的结构差异，而这些区域通常是肠道病毒的抗原位点。通过免疫测定，我们确定了两个CVA6特异性线性B细胞表位（分别命名为P42和P59），它们分别位于VP1的GH环和C末端区域，这与基于结构的抗原位点预测结果一致。我们的研究结果阐明了CVA6 VLP作为一种强大疫苗候选物的结构基础和重要抗原位点，也为肠道病毒原体组装提供了见解。柯萨奇病毒A6（CVA6）正成为导致手足口病（HFMD）的主要病原体之一，给儿童和成人带来了显著的发病率和死亡率。然而，目前尚无预防CVA6感染可用的疫苗。我们之前的研究表明，CVA6重组病毒样颗粒（VLP）是一种很有前景的CVA6疫苗候选物。在此，我们展示了通过冷冻电子显微镜确定的CVA6 VLP的3.0 Å结构。CVA6 VLP的整体结构与肠道病毒71型（EV71）和柯萨奇病毒A16（CVA16）的扩展结构相似，但仔细的结构比较发现，这些颗粒的每个衣壳蛋白的表面暴露环和C末端存在显著差异。此外，我们确定了两个CVA6特异性线性B细胞表位，并分别将它们定位到VP1的GH环和C末端区域。总的来说，我们的研究结果为CVA6 VLP疫苗开发提供了结构基础和重要的抗原信息。
