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Assay Method Information

Assay Name:  Time Resolved Fluorescence Resonance Energy Transfer (TR-FRET) Assay
Description:  The binding of compounds to bromodomain BRD4 (44-168), BRD4 (333-460), and BRD4 (1-477 or 44-460) was assessed using a time resolved fluorescent resonance energy transfer binding assay (1), that measures the binding of a fluorescently labeled probe molecule to the bromodomain protein. The bromodomain protein, fluorescent probe molecule (either a biotinylated histone peptide or a fluorescently labeled small molecule), and dose-responded test compound are incubated together to reach thermodynamic equilibrium. In the absence of a test compound, the bromodomain and small molecule are bound, resulting in a high fluorescent signal. In the presence of a sufficient concentration of inhibitor, this interaction is disrupted resulting in a loss of fluorescent resonance energy transfer. All assay components were dissolved in buffer composition 20 mM Hepes pH 7.5, 150 mM NaCl, 5 mM DTT, 0.005% Tween 20, and 100 ug/ml BSA for BRD4 (1-477 and 44-460). The final concentrations of the bromodomain proteins are 1.6 nM BRD4(44-168), 1 nM BRD4(333-460), and 1 nM BRD4(1-477 or 44-460), and the fluorescent probe molecule is 100 nM, 50 nM, and 7.5 nM respectively. All proteins were biotinylated. A streptavidin labeled with terbium cryptate (Cisbio SA-Tb) was used as detection, and pre-mixed with the bromodomain protein at a final concentration of 0.2 nM. In some instances for BRD4 (44-460), anti-His terbium cryptate was used as a detection. 7.5 nl of dose-responded test compound or DMSO vehicle (0.0375%) was pre-spotted in a black Corning 384 well plate and 10 ul each of bromodomain/detection reagent and fluorescent small molecule solution were added to the plate, and the reaction incubated for 60 min at room temperature. Plates were then read on EnVision plate reader, (λex=340 nm, acceptor λEm=520 nm, and donor λEm=615 nm, LANCE D400 mirror). Time resolved fluorescence intensity measurements were made at both emissions, and the ratio of acceptor/donor was calculated and used for data analysis.
Affinity data for this assay
 

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Last update November 1, 2007
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