The Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, USA.
Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA.
J Virol. 2019 Mar 5;93(6). doi: 10.1128/JVI.01479-18. Print 2019 Mar 15.
Human noroviruses (NoVs) are the main cause of epidemic and sporadic gastroenteritis. Phylogenetically, noroviruses are divided into seven genogroups, with each divided into multiple genotypes. NoVs belonging to genogroup II and genotype 4 (GII.4) are globally most prevalent. Genetic diversity among the NoVs and the periodic emergence of novel strains present a challenge for the development of vaccines and antivirals to treat NoV infection. NoV protease is essential for viral replication and is an attractive target for the development of antivirals. The available structure of GI.1 protease provided a basis for the design of inhibitors targeting the active site of the protease. These inhibitors, although potent against the GI proteases, poorly inhibit the GII proteases, for which structural information is lacking. To elucidate the structural basis for this difference in the inhibitor efficiency, we determined the crystal structure of a GII.4 protease. The structure revealed significant changes in the S2 substrate-binding pocket, making it noticeably smaller, and in the active site, with the catalytic triad residues showing conformational changes. Furthermore, a conserved arginine is found inserted into the active site, interacting with the catalytic histidine and restricting substrate/inhibitor access to the S2 pocket. This interaction alters the relationships between the catalytic residues and may allow for a pH-dependent regulation of protease activity. The changes we observed in the GII.4 protease structure may explain the reduced potency of the GI-specific inhibitors against the GII protease and therefore must be taken into account when designing broadly cross-reactive antivirals against NoVs. Human noroviruses (NoVs) cause sporadic and epidemic gastroenteritis worldwide. They are divided into seven genogroups (GI to GVII), with each genogroup further divided into several genotypes. Human NoVs belonging to genogroup II and genotype 4 (GII.4) are the most prevalent. Currently, there are no vaccines or antiviral drugs available for NoV infection. The protease encoded by NoV is considered a valuable target because of its essential role in replication. NoV protease structures have only been determined for the GI genogroup. We show here that the structure of the GII.4 protease exhibits several significant changes from GI proteases, including a unique pairing of an arginine with the catalytic histidine that makes the proteolytic activity of GII.4 protease pH sensitive. A comparative analysis of NoV protease structures may provide a rational framework for structure-based drug design of broadly cross-reactive inhibitors targeting NoVs.
人类诺如病毒（NoV）是引起散发和暴发胃肠炎的主要原因。从系统发生上看，诺如病毒分为 7 个基因组（GI 至 GVII），每个基因组进一步分为多个基因型。属于基因组 II 和基因型 4（GII.4）的 NoV 在全球最为流行。NoV 的遗传多样性和新型株的周期性出现给 NoV 感染疫苗和抗病毒药物的开发带来了挑战。NoV 蛋白酶对于病毒复制至关重要，是开发抗病毒药物的一个有吸引力的靶点。GI.1 蛋白酶的现有结构为靶向蛋白酶活性位点的抑制剂设计提供了基础。这些抑制剂虽然对 GI 蛋白酶具有很强的抑制作用，但对缺乏结构信息的 GII 蛋白酶抑制作用较差。为了阐明抑制剂效率差异的结构基础，我们测定了 GII.4 蛋白酶的晶体结构。该结构显示，S2 底物结合口袋发生了显著变化，使其明显变小，同时活性位点的催化三联体残基发生构象变化。此外，一个保守的精氨酸插入到活性位点，与催化组氨酸相互作用，限制了底物/抑制剂进入 S2 口袋。这种相互作用改变了催化残基之间的关系，可能允许蛋白酶活性的 pH 依赖性调节。我们在 GII.4 蛋白酶结构中观察到的变化可以解释 GI 特异性抑制剂对 GII 蛋白酶活性的抑制作用降低，因此在设计针对 NoV 的广谱交叉反应性抗病毒药物时必须考虑这些变化。
人类诺如病毒（NoV）导致全球散发和暴发胃肠炎。它们分为七个基因组（GI 至 GVII），每个基因组进一步分为几个基因型。属于基因组 II 和基因型 4（GII.4）的人类 NoV 最为流行。目前，尚无针对 NoV 感染的疫苗或抗病毒药物。由于 NoV 编码的蛋白酶在复制中具有重要作用，因此被认为是一个有价值的靶标。仅确定了 GI 基因组的 NoV 蛋白酶结构。我们在这里表明，GII.4 蛋白酶的结构与 GI 蛋白酶有几个显著差异，包括独特的精氨酸与催化组氨酸配对，使 GII.4 蛋白酶的蛋白水解活性对 pH 敏感。对 NoV 蛋白酶结构的比较分析可为针对 NoV 的广谱交叉反应抑制剂的基于结构的药物设计提供合理的框架。
