| Assay Method Information | |
| | Binding Assay |
| Description: | A human STING [3H] 2′,3′-cGAMP scintillation proximity competition binding assay was utilized to detect binding of compounds to STING protein. The competition binding assay was conducted with either a wild-type (WT, SEQ ID NO: 1) or an AQ variant (SEQ ID NO: 2) of truncated human STING protein that lacks the N-terminal four transmembrane domains and contains amino acids 155-379. The protein encoding plasmid contained a HIS tag, followed by an Avi tag and then a SUMO tag, which were followed by the STING coding sequence within the pET-28a (+) vector. The plasmid was transfected into a BL21 (DE3)/BirA E. coli co-expression strain. Protein was purified from the bacterial lysate using a cobalt-affinity column. The purified protein was dialyzed against PBS and then 20% glycerol was added prior to storage at −80° C.The assay was conducted in a 384-well plate containing final concentration of 25 nM biotin-STING protein and 17.5 nM [3H] 2′,3′-cGAMP in assay buffer (50 mM Tris pH 7.5, 100 mM NaCl, 0.1% Fatty Acid Free BSA). Test compounds (2.5 μL) were added to the plate first followed by a 25 μL mixture of STING protein, streptavidin PVT SPA beads (Perkin Elmer) and 10 μL [3H] 2′,3′-cGAMP. Plates were incubated at room temperature for 18 hrs and read on a Wallac MicroBeta TriLux (Perkin Elmer). 2′,2′-cGAMP was used as a reference compound and had an IC50 of 0.562 μM using the WT STING protein and 0.098 M using the AQ STING protein. |
| Affinity data for this assay | |
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