Targeting a key disulfide linkage to regulate RIG-I condensation and cytosolic RNA-sensing

Maintaining innate immune homeostasis is critical for preventing infections and autoimmune diseases but effective interventions are lacking. Here we identified C864–C869-mediated intermolecular disulfide-linkage formation as a critical step for human RIG-I activation that can be bidirectionally regulated to control innate immune homeostasis. The viral-stimulated C864–C869 disulfide linkage mediates conjugation of an SDS-resistant RIG-I oligomer, which prevents RIG-I degradation by E3 ubiquitin-ligase MIB2 and is necessary for RIG-I to perform liquid–liquid phase separation to compartmentalize downstream signalsome, thereby stimulating type I interferon signalling. The corresponding C865S ‘knock-in’ caused an oligomerization defect and liquid–liquid phase separation in mouse RIG-I, which inhibited innate immunity, resulting in increased viral load and mortality in mice. Using unnatural amino acids to generate covalent C864–C869 linkage and the development of an interfering peptide to block C864–C869 residues, we bidirectionally regulated RIG-I activities in human diseases. These findings provide in-depth insights on mechanism of RIG-I activation, allowing for the development of methodologies that hold promising implications in clinics.