Structural basis for ubiquitin-mediated antiviral signal activation by RIG-I

RIG-I protein recognizes viral duplex RNA with a 5′-triphosphate group, activating innate immune responses; a crystal structure of its tetrameric CARD signalling domain reveals that non-covalently linked ubiquitin chains stabilize the tetramer in a ‘lock-washer’ structure that serves as a signalling platform for the recruitment and activation of MAVS.