松毛虫T4病毒衣壳结构及病毒衣壳分子进化

The tetraviruses (Tetraviridae) are a family of viruses with non-enveloped T=4 capsids that package single stranded, positive-sense RNA genomes and infect only a single order of insects, the Lepidoptera (moths & butterflies). The family Tetraviridae is the only RNA virus family that has a restrictive host range to insects and a non-enveloped T=4 particle. According to its genomic organization and particle surface structure, the family Tetraviridae is separated into two genera, i.e. betatetravirus and omegatetravirus. Betatetravirus contains a monopartite genome and its capsid has distinct pits between surface protrusions that are easily visualized via cryoEM, while omegatetravirus has a bipartite genomes and its capsid has oval protrusions on its surface. Evidence suggests that the omega-like viral particle packages both RNA strands, while the beta-like viral particle often packages an additional subgenomic RNA that encodes the capsid protein. Thus, both beta and omega tetraviruses contain two RNA molecules, as do nodaviruses, the only other small, spherical RNA animal viruses with a bipartite genome. Moreover, the capsid proteins of tetraviruses undergo a post-assembly, autocatalytic cleavage that is required for viral infectivity. As one of the simplest viruses to undergo such an autocatalytic cleavage, tetraviruses is recognized as an ideal model to study non-envelope virus entry into host cells and the mechanism of viral particle assembly and autoproteolysis. Dendrolimus punctatus tetravirus (DpV) has been identi?ed by our group as a new member of the genus Omegatetravirus that is related serologically to Nudaurelia capensis ω virus (NωV) . DpV is also the first identified tetravirus in China. Our preliminary studies suggest that the surface structure of DpV is more like betatetravirus, rather than beta-like NωV, leading us to wonder if the classification standard of Tetraviridae should be reconsidered and highlight the importance of this project to further study the viral structure of DpV. Moreover, we will use DpV as a model organism to study the mechanisms of viral particle assembly, capsid autoproteolysis, and the infectivity of DpV. Furthermore, since nodaviruses have similar structure with betatetravirus and similar bipartite RNA genome like omegatetravirus, it is believed by many virologists that there exists evolutional link between tetravirus and nodavirus. More interestingly, DpV has a beta-like structure and a omega-like genome organization, making it the tetravirus most resembling nodavirus. Considering nodavirus is another research focus of our group, we will compare these two viruses, and try to uncover the evolutional linkage between these two important virus families. The accomplishment of this project will significantly deepen our understanding to tetravirus, provide the insights into the mechanisms of viral capsid autoproteolysis and non-enveloped virus infectivity, and the molecular evolution theory of viruses.

松毛虫T4病毒是我国目前为止发现的唯一的一株T4科病毒，和国内外首次在松毛虫中发现的T4病毒，国际病毒分类命名委员会2009年将其命名为松毛虫病毒（DpV）。这一科病毒的命名是以病毒结构特点命名的唯一的科。所以其病毒衣壳三维结构的特点和相关进化研究，具有重要的研究意义。但是由于松毛虫T4病毒的衣壳结构更加类似于β病毒属，而不是应该归属的ω属。使我们对T4病毒两个属的基本分类标准是否合适产生疑问。T4病毒是为数不多的在病毒装配成熟阶段需要病毒衣壳蛋白前体自我剪切完成病毒粒子成熟的病毒类群。我们初步研究发现，表达的病毒前体蛋白不但能够组装成病毒样粒子，而且病毒衣壳也发生了自我剪切。我们有兴趣，进一步深入对这种衣壳蛋白自我剪切在病毒衣壳装配中的作用及意义进行研究。T4科病毒和野田村科病毒的衣壳蛋白具有非常相似的结构，推测T4科病毒的衣壳蛋白可能由野田村科病毒进化而来，我们将予以证实。

T4 病毒科（Tetraviridae）是唯一根据其病毒衣壳结构(T=4)划分的病毒科，属于正链RNA病毒。2011年，根据其基因组结构等的区别，T4病毒科又被国际分类委员会（ICTV）进一步划分为三个科，即Alphatetraviridae（阿尔法T4病毒），Carmotetraviridae与Permutotetraviridae。T4病毒衣壳三维结构的特点和相关进化研究，具有重要的研究意义。松毛虫T4 病毒(DpTV)是在中国境内发现的唯一一株T4病毒，有本课题主持人发现并鉴定，属于阿尔法T4病毒科。松毛虫T4 病毒的衣壳结构更加类似于其中的β T4病毒属，而非应该归属的ω属，且与野田村病毒（另一种本课题组主要研究的正链RNA病毒科）的衣壳蛋白在结构与氨基酸序列上具有一定的相似性。因此，我们对其衣壳蛋白的结构、与野田村病毒的进化关系、其病毒衣壳蛋白前体自我剪切完成病毒粒子成熟的分子机制、其病毒RNA的复制机制等科学问题有着非常浓厚的科学兴趣，并在本课题的支持下，在这些方面进行了一系列的研究，也取得了较好的成果。在DpTV衣壳结构方面，我们通过与中国科技大学相关团队的合作，利用冷冻电镜对其衣壳进行了大量分析，取得了一定的数据。我们还发现了DpTV编码的Hel蛋白的RNA解旋酶功能，并解析了其生化特征。这是首次在T4病毒科中确定了病毒解旋酶活性，对我们理解T4病毒的核酸复制机制具有重要的科学意义。