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Structural basis of viral RNA recognition by RIG-I-like receptors

Structural Basis of Viral RNA Recognition by RIG-I-Like Receptors. (August 2012) Cheng Lu, B.S., Nankai University, China Chair of Advisory Committee: Dr. Pingwei Li RIG-I-like receptors (RLRs), RIG-I, MDA5, and LGP2, are a family of innate immune receptors that recognize viral RNA in the cytoplasm and initiate antiviral responses including the induction of type I interferons and other pro-inflammatory cytokines. All three proteins have both an RNA helicase domain with ATPase activity and a C-terminal domain (CTD) which is responsible for RNA binding. RIG-I and MDA5 also have two tandem caspase activation and recruitment domains (CARDs) at the N-terminus which are involved in downstream signaling. To understand the structural basis of viral RNA recognition by the RLRs, especially RIG-I, we have performed extensive biochemical studies to determine the binding properties of RIG-I with different forms of RNA, including dsRNA with and without 5'-triphosphate (5'-ppp) groups, and 5'-ppp ssRNA. RIG-I CTD binds to these forms of RNA, and exhibits the highest affinity for 5'-ppp dsRNA. We also determined the crystal structures of RIG-I CTD in complex with dsRNA with and without 5'-ppp by X-ray crystallography. The structures showed that RIG-I recognizes the termini of the dsRNA and interacts with the two types of RNA in different orientations. By comparing these complex structures together with mutagenesis studies, we conclude that RIG-I