Greehey Children's Cancer Research Institute, University of Texas Health at San Antonio, San Antonio, TX, USA.
Department of Biochemistry and Structural Biology, University of Texas Health at San Antonio, San Antonio, TX, USA.
Nat Commun. 2021 Jun 2;12(1):3287. doi: 10.1038/s41467-021-23594-y.
The SARS-CoV-2 nsp16/nsp10 enzyme complex modifies the 2'-OH of the first transcribed nucleotide of the viral mRNA by covalently attaching a methyl group to it. The 2'-O methylation of the first nucleotide converts the status of mRNA cap from Cap-0 to Cap-1, and thus, helps the virus evade immune surveillance in host cells. Here, we report two structures of nsp16/nsp10 representing pre- and post-release states of the RNA product (Cap-1). We observe overall widening of the enzyme upon product formation, and an inward twisting motion in the substrate binding region upon product release. These conformational changes reset the enzyme for the next round of catalysis. The structures also identify a unique binding mode and the importance of a divalent metal ion for 2'-O methylation. We also describe underlying structural basis for the perturbed enzymatic activity of a clinical variant of SARS-CoV-2, and a previous SARS-CoV outbreak strain.
SARS-CoV-2 的 nsp16/nsp10 酶复合物通过将一个甲基共价连接到病毒 mRNA 的第一个转录核苷酸的 2'-OH 上来修饰它。第一个核苷酸的 2'-O 甲基化将 mRNA 帽的状态从 Cap-0 转换为 Cap-1，从而帮助病毒逃避宿主细胞中的免疫监视。在这里，我们报告了 nsp16/nsp10 的两种结构，代表了 RNA 产物（Cap-1）的释放前和释放后的状态。我们观察到产物形成时酶的整体变宽，以及产物释放时底物结合区域的向内扭曲运动。这些构象变化为下一轮催化重置了酶。这些结构还确定了 2'-O 甲基化的独特结合模式和二价金属离子的重要性。我们还描述了 SARS-CoV-2 的临床变异株和之前 SARS-CoV 爆发株的酶活性受到干扰的潜在结构基础。
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