Cysteine allostery and autoinhibition govern human STING oligomer functionality.

The stimulator of interferon genes (STING) innate immune pathway can exacerbate inflammatory diseases when aberrantly activated, emphasizing an unmet need for STING antagonists. However, no inhibitors have advanced to the clinic because it remains unclear which mechanistic step(s) of human STING activation are crucial for inhibition of downstream signaling. Here we report that C91 palmitoylation is not universally necessary for human STING signaling. Instead, evolutionarily-conserved C64 is basally palmitoylated and is crucial for preventing unproductive STING oligomerization. The effects of palmitoylation at C64 and C91 converge on the control of intradimer disulfide bond formation at C148. Together, dynamic equilibria of these cysteine post-translational modifications allow proper STING ligand-binding domain self-assembly and scaffolding function. Given this complex landscape, we took inspiration from STING's natural autoinhibitory mechanism and identified an eight-amino-acid peptide that binds a defined pocket at the oligomerization interface, setting the stage for future therapeutic development.