A Conserved PLPLRT/SD Motif of STING Mediates the Recruitment and Activation of TBK1

Nucleic acids from bacteria or viruses induce potent immune responses in infected cells(1–4). The detection of pathogen-derived nucleic acids is a central strategy by which the host senses infection and initiates protective immune responses(5,6). Cyclic GMP-AMP synthase (cGAS) is a double-stranded DNA sensor(7,8). It catalyzes the synthesis of cyclic GMP-AMP (cGAMP)(9–12), which stimulates the induction of type I interferons (IFN-Is) through the STING-TBK1-IRF-3 signaling axis(13–15). Stimulator of interferon genes (STING) oligomerizes upon cGAMP binding, leading to the recruitment and activation of tank-binding kinase 1 (TBK1)(8,16). Interferon regulatory factor 3 (IRF-3) is then recruited to the signaling complex and activated by TBK1(8,17–20). Phosphorylated IRF-3 translocates to the nucleus and initiates the expression of IFN-Is(21). However, the precise mechanisms governing STING activation by cGAMP and subsequent TBK1 activation by STING remained poorly understood. Here we show that a conserved PLPLRT/SD motif within the C-terminal tail of STING mediates the recruitment and activation of TBK1. Crystal structures of TBK1 bound to STING reveal that the PLPLRT/SD motif binds to the dimer interface of TBK1. Cell-based studies confirm that the direct interaction between TBK1 and STING is essential for IFN-β induction upon cGAMP stimulation. Moreover, we show that full-length STING oligomerizes upon cGAMP binding and highlight this as an essential step in the activation of STING-mediated signaling.