The Structural Basis of 5' Triphosphate Double-Stranded RNA Recognition by RIG-I C-Terminal Domain.

Summary RIG-I is a cytosolic sensor of viral RNA that plays crucial roles in the induction of type I interferons. The C-terminal domain (CTD) of RIG-I is responsible for the recognition of viral RNA with 5′ triphosphate (ppp). However, the mechanism of viral RNA recognition by RIG-I is still not fully understood. Here, we show that RIG-I CTD binds 5′ ppp dsRNA or ssRNA, as well as blunt-ended dsRNA, and exhibits the highest affinity for 5′ ppp dsRNA. Crystal structures of RIG-I CTD bound to 5′ ppp dsRNA with GC- and AU-rich sequences revealed that RIG-I recognizes the termini of the dsRNA and interacts with the 5′ ppp through extensive electrostatic interactions. Mutagenesis and RNA-binding studies demonstrated that similar binding surfaces are involved in the recognition of different forms of RNA. Mutations of key residues at the RNA-binding surface affected RIG-I signaling in cells.