Institute of Technology, University of Tartu, Nooruse 1, 50411 Tartu, Estonia.
The Pirbright Institute, Ash Road, Pirbright GU24 ONF, UK.
Viruses. 2022 Jun 17;14(6):1327. doi: 10.3390/v14061327.
Alphaviruses are positive-strand RNA viruses, mostly being mosquito-transmitted. Cells infected by an alphavirus become resistant to superinfection due to a block that occurs at the level of RNA replication. Alphavirus replication proteins, called nsP1-4, are produced from nonstructural polyprotein precursors, processed by the protease activity of nsP2. Trans-replicase systems and replicon vectors were used to study effects of nsP2 of chikungunya virus and Sindbis virus on alphavirus RNA replication in mosquito cells. Co-expressed wild-type nsP2 reduced RNA replicase activity of homologous virus; this effect was reduced but typically not abolished by mutation in the protease active site of nsP2. Mutations in the replicase polyprotein that blocked its cleavage by nsP2 reduced the negative effect of nsP2 co-expression, confirming that nsP2-mediated inhibition of RNA replicase activity is largely due to nsP2-mediated processing of the nonstructural polyprotein. Co-expression of nsP2 also suppressed the activity of replicases of heterologous alphaviruses. Thus, the presence of nsP2 inhibits formation and activity of alphavirus RNA replicase in protease activity-dependent and -independent manners. This knowledge improves our understanding about mechanisms of superinfection exclusion for alphaviruses and may aid the development of anti-alphavirus approaches.
甲病毒是正链 RNA 病毒，主要通过蚊子传播。感染甲病毒的细胞由于在 RNA 复制水平上发生的阻断而对再感染产生抗性。甲病毒复制蛋白，称为 nsP1-4，由非结构多蛋白前体产生，由 nsP2 的蛋白酶活性加工。使用转录复制酶系统和复制子载体来研究基孔肯雅病毒和辛德毕斯病毒的 nsP2 对蚊细胞中甲病毒 RNA 复制的影响。共表达的野生型 nsP2 降低了同源病毒的 RNA 复制酶活性；这种效应通过 nsP2 蛋白酶活性位点的突变而降低，但通常不会被消除。阻断 nsP2 对其切割的复制酶多蛋白突变降低了 nsP2 共表达的负效应，证实 nsP2 介导的 RNA 复制酶活性抑制主要是由于 nsP2 介导的非结构多蛋白的加工。nsP2 的共表达也抑制了异源甲病毒复制酶的活性。因此，nsP2 的存在以依赖和不依赖蛋白酶活性的方式抑制了甲病毒 RNA 复制酶的形成和活性。这一知识提高了我们对甲病毒超感染排除机制的理解，并可能有助于开发抗甲病毒的方法。
