CHEMBL5731375

Time-Resolved Fluorescence Resonance Energy Transfer (TR-FRET) : The in-house BTK corresponds to recombinant human catalytic domain (aa 393-659), which was expressed in SF9 cells with an N-terminal his tag and purified by immobilized metal affinity chromatography. BTK was mixed with peptide substrate (biotin-TYR1, Sequence: Biotin-(Ahx)-GAEEEIYAAFFA-COOH, 0.2 μM final) at varying inhibitor concentrations in reaction buffer: 50 mM MOPSO pH 6.5, 10 mM MgCl2, 2 mM MnCl2, 2.5 mM DTT, 0.01% BSA, 0.1 mM Na3VO4 and 0.001 mM ATP. After about 60 mM incubation at room temperature, the reaction was quenched by addition of EDTA (final concentration: 100 mM) and developed by addition of detection reagents (final approximate concentrations: 30 mM HEPES pH 7.0, 0.06% BSA, 0.006% Tween-20, 0.24 M KF, 80 ng/mL PT66K (europium labeled anti-phosphotyrosine antibody cat #61T66KLB Cisbio, Bedford, Mass.) and 0.6 μg/mL SAXL (Phycolink streptavidin-allophycocyanin acceptor, cat #PJ25S, Prozyme, San Leandro, Calif.). The developed reaction was incubated in the dark for about 60 mM at room temperature, then read via a time-resolved fluorescence detector (Rubystar, BMG) using a 337 nm laser for excitation and monitoring emission wavelength at 665 nm. Within the linear range of the assay, the observed signal at 665 nm was directly related to phosphorylated product and can be used to calculate the IC50 values.