Identification And Characterization Of Enterovirus 71 Nonstructural Protein 2C

RNA helicases and chaperones are the two major classes of RNA remodeling proteins, which function to remodel RNA structures and/or RNA-protein interactions, and are required for all aspects of RNA metabolism. For viruses, although some virus-encoded RNA helicases/chaperones have been predicted or identified, their RNA remodeling activities in vitro and functions in viral life cycle largely remain elusive. Enteroviruses are a large group of positive-stranded RNA viruses in the Picornaviridae family, which include numerous important human pathogens. Here we report that the nonstructural protein 2C of enterovirus 71 (EV71), which is the major causative pathogen of hand-foot-and-mouth disease (HFMD) and has been regarded as the most important neurotropic enterovirus after poliovirus eradication, is able to function not only as an RNA helicase that 3'-to-5' unwinds RNA helices ATP-dependently, but also as an RNA chaperone that destabilizes helices bidirectionally and facilitates strand annealing and complex RNA structure formation ATP-independently. We also determined that the helicase activity of EV712C is based on its middle helicase core domain, while the C-terminal domain is indispensable for its RNA chaperoning activity. Protein 2C facilitated EV71 RNA synthesis in vitro by promoting (-)-RNA template recycling; and when the 2C helicase activity was impaired, EV71 RNA replication and virion production were mostly abolished in cells, indicating that 2C-mediated RNA remodeling plays critical roles in enteroviral life cycle. Furthermore, we find that the RNA helicase and chaperoning activities of 2C are also conserved in coxsackie A virus (CAV), another important enterovirus. Altogether, our study is the first to uncover the RNA helicase and chaperoning activities associated with enterovirus 2C, and provides both in vitro and cellular evidence for their potential roles during viral RNA replication, which sheds lights on the understanding of enteroviruses and the two types of RNA remodeling activities.