title: Structural and biochemical studies of RIG-I antiviral signaling.
abstract: Retinoic acid-inducible gene I (RIG-I) is an important pattern recognition receptor that detects viral RNA and triggers the production of type-I interferons through the downstream adaptor MAVS (also called IPS-1, CARDIF, or VISA). A series of structural studies have elaborated some of the mechanisms of dsRNA recognition and activation of RIG-I. Recent studies have proposed that K63-linked ubiquitination of, or unanchored K63-linked polyubiquitin binding to RIG-I positively regulates MAVS-mediated antiviral signaling. Conversely phosphorylation of RIG-I appears to play an inhibitory role in controlling RIG-I antiviral signal transduction. Here we performed a combined structural and biochemical study to further define the regulatory features of RIG-I signaling. ATP and dsRNA binding triggered dimerization of RIG-I with conformational rearrangements of the tandem CARD domains. Full length RIG-I appeared to form a complex with dsRNA in a 2:2 molar ratio. Compared with the previously reported crystal structures of RIG-I in inactive state, our electron microscopic structure of full length RIG-I in complex with blunt-ended dsRNA, for the first time, revealed an exposed active conformation of the CARD domains. Moreover, we found that purified recombinant RIG-I proteins could bind to the CARD domain of MAVS independently of dsRNA, while S8E and T170E phosphorylation-mimicking mutants of RIG-I were defective in binding E3 ligase TRIM25, unanchored K63-linked polyubiquitin, and MAVS regardless of dsRNA. These findings suggested that phosphorylation of RIG inhibited downstream signaling by impairing RIG-I binding with polyubiquitin and its interaction with MAVS.
authors.affiliation: State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Miao
authors.initials: M
authors.lastname: Feng
authors.forename: Zhanyu
authors.initials: Z
authors.lastname: Ding
authors.forename: Liang
authors.initials: L
authors.lastname: Xu
authors.forename: Liangliang
authors.initials: L
authors.lastname: Kong
authors.forename: Wenjia
authors.initials: W
authors.lastname: Wang
authors.forename: Shi
authors.initials: S
authors.lastname: Jiao
authors.forename: Zhubing
authors.initials: Z
authors.lastname: Shi
authors.forename: Mark I
authors.initials: MI
authors.lastname: Greene
authors.forename: Yao
authors.initials: Y
authors.lastname: Cong
authors.forename: Zhaocai
authors.initials: Z
authors.lastname: Zhou
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D006801:Humans; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D025821:Polyubiquitin / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012330:RNA, Double-Stranded / Q000378:metabolism; D011971:Receptors, Immunologic; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C505371:MAVS protein, human; D012330:RNA, Double-Stranded; D011971:Receptors, Immunologic; D011994:Recombinant Proteins; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D025821:Polyubiquitin; D000255:Adenosine Triphosphate; C084523:TRIM25 protein, human; D044767:Ubiquitin-Protein Ligases; C452820:RIGI protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases