A Two-Site Interaction Underpins TRIM25 Activation of the RIG-I Anti-Viral Response — ASN Events
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  2. Poster Session 2
  3. A Two-Site Interaction Underpins TRIM25 Activation of the RIG-I Anti-Viral Response

A Two-Site Interaction Underpins TRIM25 Activation of the RIG-I Anti-Viral Response (#307)

Akshay D'Cruz 1 2 , Nadia Kershaw 1 2 , Edmond Linossi 1 2 , Laura Dagley 1 2 , Jessica Chiang 3 , May Wang 3 , Thomas Hayman 1 2 , Jian-Guo Zhang 1 2 , Michaela Gack 3 , Nicos Nicola 1 2 , Jeffrey Babon 1 2 , Sandra Nicholson 1 2
  1. Inflammation Division, Walter & Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
  2. The University of Melbourne, Parkville, VIC, Australia
  3. Department of Microbiology & Immunobiology, Harvard Medical School, Boston, MA, United States of America

The retinoic acid-inducible gene-I (RIG-I)-like receptors are an important family of cytosolic viral RNA sensors. RIG-I recognizes short 5’-triphosphate base-paired viral RNA and is a critical mediator of the innate immune response against viruses such as influenza A, HIV and hepatitis C. This response requires a carefully orchestrated interaction with tripartite motif 25 (TRIM25). The binding of viral RNA and the hydrolysis of ATP induce a conformational change in RIG-I, which releases its tandem CARD domains for interaction with the TRIM25 B30.2 domain. TRIM25 then functions as an E3 ubiquitin ligase to stabilize the formation of a RIG-I tetramer and facilitate RIG-I interaction with MAVS (mitochondrial anti-viral signalling) at the mitochondrial membrane. The net result is expression of the type I and III interferon (IFN)s and the establishment of an anti-viral state. We have previously solved the crystal structure of the mouse TRIM25 B30.2 domain and identified key residues that are critical for the interaction with the RIG-I CARDs (Site 1) (1). We have now identified a second CARD-binding site on the TRIM25 B30.2 domain that is revealed by removal of an N-terminal alpha-helix (mimicking TRIM25 dimerization) (Site 2). We provide biochemical evidence to suggest that both CARDs participate in this interaction and that a conformational change is required to expose a structurally-similar helix in CARD2. This suggests a model whereby the RIG-I CARDs interact with opposing sides of the TRIM25 B30.2 domain to form a higher order TRIM25/RIG-I complex that facilitates RIG-I tetramerisation. The characterization of a dual binding mode for the TRIM25 B30.2 domain is a first for the SPRY/B30.2 family and has broader implications. For instance, disease-causing mutations in the MEVF gene encoding Pyrin (TRIM20) map to its B30.2 domain in a region analogous to “Site 2”.

 (1) D’Cruz et al., Biochem J. 2013.