There are currently no antiviral therapies specific against SARS-CoV-2, the virus responsible for the global pandemic disease COVID-19. To facilitate structure-based drug design, we conducted an X-ray crystallographic study of the nsp16/nsp10 2'-O-methyltransferase complex that methylates Cap-0 viral mRNAs to improve viral protein translation and to avoid host immune detection. Heterodimer structures are determined with the methyl donor S-adenosylmethionine (SAM), the reaction product S-adenosylhomocysteine (SAH) or the SAH analog sinefungin (SFG). Furthermore, structures of nsp16/nsp10 with the methylated Cap-0 analog (m7GpppA) and SAM or SAH bound were obtained. Comparative analysis revealed flexible loops in open and closed conformations at the m7GpppA binding pocket. Bound sulfates in several structures suggested the location of the phosphates in the ribonucleotide binding groove. Additional nucleotide binding sites were found on the face of the protein opposite the active site. These various sites and the conserved dimer interface could be exploited for development of antiviral inhibitors.

中文翻译：

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具有RNA Cap类似物和硫酸盐结合的SARS-CoV-2 2'-O-甲基转移酶异二聚体的结构揭示了基于结构的抑制剂设计的新策略

目前，尚无针对SARS-CoV-2（一种导致全球大流行性疾病COVID-19的病毒）的抗病毒疗法。为了促进基于结构的药物设计，我们对nsp16 / nsp10 2'-O-甲基转移酶复合物进行了X射线晶体学研究，该复合物甲基化了Cap-0病毒mRNA，从而改善了病毒蛋白翻译并避免了宿主免疫检测。异二聚体结构用甲基供体S-腺苷甲硫氨酸（SAM），反应产物S-腺苷同型半胱氨酸（SAH）或SAH类似物西芬净（SFG）确定。此外，获得具有甲基化的Cap-0类似物（m7GpppA）和SAM或SAH结合的nsp16 / nsp10的结构。对比分析显示，m7GpppA结合口袋处的开放和闭合构象均存在柔性环。几种结构中结合的硫酸盐表明磷酸在核糖核苷酸结合槽中的位置。在与活性位点相反的蛋白质面上发现了其他核苷酸结合位点。这些不同的位点和保守的二聚体界面可用于开发抗病毒抑制剂。