Paramyxovirus V Proteins Disrupt the Fold of the RNA Sensor MDA5 to Inhibit Antiviral Signaling

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Science  17 Jan 2013:
DOI: 10.1126/science.1230949

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The RIG-I like receptor MDA5 senses cytoplasmic viral RNA and activates antiviral innate immunity. To reveal how paramyxoviruses counteract this response, we determined the crystal structure of the MDA5 ATP-hydrolysis domain in complex with the viral inhibitor V protein. The V protein unfolded the ATPase domain of MDA5 via a β-hairpin motif and recognized a structural motif of MDA5 that is normally buried in the conserved helicase fold. This leads to disruption of the MDA5 ATP-hydrolysis site and prevention of RNA bound MDA5 filament formation. The structure explains why V proteins inactivate MDA5, but not RIG-I, and mutating only two amino acids in RIG-I induces robust V protein binding. Our results suggest an inhibition mechanism of RLR signalosome formation by unfolding of receptor and inhibitor.

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