The STING-null RAW264.7 cells expressing TurboID-STING were treated with DMSO or 30 μg/ml DMXAA, and 500 µM biotin was added to the medium. After 1-h incubation, the cells were lysed in 6 M guanidine-HCl containing 100 mM HEPES-NaOH (pH 7.5), 10 mM TCEP, and 40 mM CAA. The lysates were dissolved by heating and sonication, and centrifuged at 20,000 g for 15 min at 4ºC. The supernatants were recovered, and proteins were purified by methanol/chloroform precipitation and solubilized by 0.1% RapiGest SF in 50 mM triethylammonium bicarbonate. After repeated sonication and vortex, the proteins were digested with trypsin at 37ºC overnight. The resultant peptide solutions were captured on anti-biotin (A7C2A) rabbit monoclonal antibody-conjugated beads in the presence of 1 mg/ml Pefabloc SC during 3 h of incubation at 4ºC. After washing with TBS four times, and with ultrapure water twice, the biotinylated peptides were eluted with 100 µL of 0.2% TFA and 80% ACN twice. The combined eluates were desalted using GL-Tip SDB, evaporated in a SpeedVac concentrator, and redissolved in 0.1% TFA and 3% ACN.