The superfamily-1 helicase non-structural protein 13 (nsp13) is required for SARS-CoV-2 replication, making it an important antiviral therapeutic target. The mechanism and regulation of nsp13 has not been explored at the single-molecule level. Specifically, force-dependent unwinding experiments have yet to be performed for any coronavirus helicase. Here, using optical tweezers, we find that nsp13 unwinding frequency, processivity, and velocity increase substantially when a destabilizing force is applied to the dsRNA, suggesting a passive unwinding mechanism. These results, along with bulk assays, depict nsp13 as an intrinsically weak helicase that can be potently activated by picoNewton forces. Such force-dependent behavior contrasts the known behavior of other viral monomeric helicases, drawing stronger parallels to ring-shaped helicases. Our findings suggest that mechanoregulation, which may be provided by a directly bound RNA-dependent RNA polymerase, enables on-demand helicase activity on the relevant polynucleotide substrate during viral replication.

中文翻译：

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SARS-CoV-2 nsp13解旋酶的作用力依赖的解链RNA刺激。

SARS-CoV-2复制需要superfamily-1解旋酶非结构蛋白13（nsp13），使其成为重要的抗病毒治疗靶标。nsp13的机制和调控尚未在单分子水平上进行探讨。具体而言，尚未针对任何冠状病毒解旋酶进行依赖于力的展开实验。在这里，使用光镊，我们发现当对dsRNA施加去稳定力时，nsp13的解链频率，连续性和速度会大大提高，这表明存在被动解链机制。这些结果与大量测定一起描述了nsp13是一种固有的弱解旋酶，可以被picoNewton力有效激活。这种依赖于力的行为与其他病毒单体解旋酶的已知行为形成对比，与环状解旋酶的相似性更强。