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C-terminal domain of Retinoic acid-inducible gene (RIG)-I-like Receptors Retinoic acid-inducible gene (RIG)-I-like Receptors (RLRs) are cytoplasmic RNA receptors that recognize non-self RNA and act as molecular sensors to detect viral pathogens. They play crucial roles in innate antiviral responses, including the production of proinflammatory cytokines and type I interferon. There are three RLRs in vertebrates, RIG-I, LGP2, and MDA5. They are characterized by a central DExD/H-box helicase domain and a C-terminal domain, both of which are responsible for binding viral RNA. The helicase domain catalyzes the unwinding of double stranded RNA in an ATP-dependent manner. RIG-I and MDA5 also contain two N-terminal caspase activation and recruitment domains (CARDs), which initiate downstream signaling upon viral RNA sensing. They may detect partially overlapping viral substrates, including dengue virus, West Nile virus (WNV), reoviruses, and several paramyxoviruses (such as measles virus and Sendai virus). LGP2 lacks CARD and may play a regulatory role in RLR signaling. It may cooperate with either RIG-I or MDA5 to sense viral RNA.
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