A conserved isoleucine in the binding pocket of RIG-I controls immune tolerance to mitochondrial RNA
Ann Kristin de Regt, K. Anand, Katrin Ciupka, F. Bender, Karl Gatterdam, Bastian Putschli, David Fusshöller, Daniel Hilbig, Alexander Kirchhoff, Charlotte Hunkler, Steven Wolter, Agathe Grünewald, Christina Wallerath, Christine Schuberth-Wagner, János Ludwig, Katrin Paeschke, Eva Bartok, Gregor Hagelueken, Gunther Hartmann, Thomas Zillinger, Matthias Geyer, Martin Schlee
Abstract
RIG-I is a cytosolic receptor of viral RNA essential for the immune response to numerous RNA viruses. Accordingly, RIG-I must sensitively detect viral RNA yet tolerate abundant self-RNA species. The basic binding cleft and an aromatic amino acid of the RIG-I C-terminal domain(CTD) mediate high-affinity recognition of 5'triphosphorylated and 5'base-paired RNA(dsRNA). Here, we found that, while 5'unmodified hydroxyl(OH)-dsRNA demonstrated residual activation potential, 5'-monophosphate(5'p)-termini, present on most cellular RNAs, prevented RIG-I activation. Determination of CTD/dsRNA co-crystal structures and mutant activation studies revealed that the evolutionarily conserved I875 within the CTD sterically inhibits 5'p-dsRNA binding. RIG-I(I875A) was activated by both synthetic 5'p-dsRNA and endogenous long dsRNA within the polyA-rich fraction of total cellular RNA. RIG-I(I875A) specifically interacted with long, polyA-bearing, mitochondrial(mt) RNA, and depletion of mtRNA from total RNA abolished its activation. Altogether, our study demonstrates that avoidance of 5'p-RNA recognition is crucial to prevent mtRNA-triggered RIG-I-mediated autoinflammation.