Structural and mechanistic studies of multifunctional proteases in virus replication and host immune evasion

多蛋白的合成和翻译后切割是正链（+）RNA病毒常用的基因组表达策略。将多蛋白切割成功能单位对病毒来说是必不可少的，这是由病毒编码的蛋白酶进行的，其中许多蛋白酶也针对细胞蛋白来破坏宿主的抗病毒反应并协助病毒复制。我的NSERC研究项目探索了病毒蛋白酶在+RNA病毒复制和宿主免疫逃避策略中的多功能作用的分子基础。***我目前关注的是来自尼多病毒目的+RNA病毒，该目包含对动物和人类具有重要意义的病毒，包括动脉病毒，如马动脉炎病毒（EAV）和猪生殖与呼吸综合征病毒（PRRSV），以及严重急性呼吸综合征（SARS）和新兴中东呼吸综合征（MERS）冠状病毒。这些病毒表达两种多蛋白，其中包含许多非结构蛋白（nsps），其中一个子集包括活性蛋白酶结构域。PLP2和PLpro是分别位于动脉病毒和冠状病毒nsp2和nsp3内的蛋白酶。值得注意的是，除了作为切割病毒多蛋白位点的内肽酶外，它们还作为异肽酶从细胞蛋白中去除翻译后修饰蛋白泛素（Ub）和ISG15，以抑制Ub和ISG15依赖的宿主抗病毒途径。相反，nsp1ß是PRRSV的一种蛋白酶，也参与多蛋白切割，但其辅助功能是通过与宿主蛋白PCBP2形成RNA结合复合体来辅助病毒复制，以控制程序性核糖体移框事件，从而在病毒基因组翻译过程中产生额外的病毒蛋白。***利用分子生物学和结构生物学的方法，我的目标是详细了解PLP2， PLpro和nsp1ß在病毒生命周期中发挥的不同作用。我将确定使PLP2和PLpro能够破坏Ub和isg15依赖的抗病毒途径的结构特征，基于紧密结合的Ub突变体开发PLP2和PLpro抑制剂，以探索其底物结合特性和催化机制，并揭示nsp1ß如何与PCBP2形成RNA结合复合物以控制核糖体移框。***该研究将对病毒蛋白酶如何破坏宿主抗病毒反应和指导病毒蛋白的非规范翻译产生重要的新见解，使其成为病毒学家，生物化学家和细胞生物学家的广泛兴趣。参与研究的学员将受益于结构和分子生物学的高生产力研究计划。他们将获得所需的技能，成为学术界或工业界的高素质人才，在这些领域需要分子和结构生物学、生物化学和生物技术的工作知识

The synthesis and posttranslational cleavage of polyproteins is a common genome expression strategy used by positive-strand (+)RNA viruses. Cleavage of the polyproteins into functional units is essential to the virus and is carried out by virus-encoded proteases, many of which also target cellular proteins to disrupt host antiviral responses and to assist with virus replication. My NSERC research program explores the molecular basis underlying the multifunctional role of viral proteases in the replication and host immune evasion strategies of +RNA viruses.***I currently focus on +RNA viruses from the order Nidovirales, which contains viruses of animal and human importance, including arteriviruses, such as equine arteritis virus (EAV) and porcine reproductive and respiratory syndrome virus (PRRSV), as well as the severe acute respiratory syndrome (SARS) and the emerging Middle-East respiratory syndrome (MERS) coronaviruses. These viruses express two polyproteins that contain a number of non-structural proteins (nsps), a subset of which include active protease domains. PLP2 and PLpro are proteases located within nsp2 and nsp3 of arteriviruses and coronaviruses, respectively. Remarkably, in addition to acting as endopeptidases that cleave sites in the viral polyproteins, they also act as isopeptidases to remove the posttranslational modifier proteins ubiquitin (Ub) and ISG15 from cellular proteins to suppress Ub- and ISG15-dependent host antiviral pathways. In contrast, nsp1ß is a protease of PRRSV that also participates in polyprotein cleavage, yet its ancillary function is to assist virus replication by forming an RNA binding complex with the host protein PCBP2 to control programmed ribosomal frameshifting events that yield additional viral proteins during virus genome translation.***Using molecular and structural biology methods, I aim to provide a detailed understanding of the diverse roles that PLP2, PLpro and nsp1ß play during the virus life cycle. I will identify the structural features that enable PLP2 and PLpro to disrupt Ub- and ISG15-dependent antiviral pathways, develop inhibitors of PLP2 and PLpro based on tight-binding Ub mutants to probe their substrate binding properties and catalytic mechanisms, and reveal how nsp1ß forms an RNA binding complex with PCBP2 to control ribosomal frameshifting.***The research will yield important new insights into how viral proteases subvert host antiviral responses and direct the non-canonical translation of viral proteins, making it of wide interest to virologists, biochemists and cell biologists. Trainees engaged in the research will benefit from a highly productive research program in structural and molecular biology. They will gain the skills they need to become highly qualified personnel in academia or industry where a working knowledge of molecular and structural biology, biochemistry and biotechnology is required.**