CHEMBL5730686

FP Competitive Binding Assay (No.350): Fluorescence Polarization (FP) competitive binding studies (see above) were carried out using the FAM labeled fluorescent probe Cpd. No. 350 to determine binding affinities of representative compounds to both BD1 and BD2 of BRD2, BRD3, and BRD4 proteins. Equilibrium dissociation constants (Id) values of Cpd. No. 350 to these six proteins were determined from protein saturation experiments by monitoring the total fluorescence polarization of mixtures composed with the fluorescent probe at a fixed concentration and proteins with increasing concentrations up to full saturation. Serial dilutions of testing protein were mixed with Cpd. No. 350 to a final volume of 200 μl in the assay buffer. In order to achieve large dynamic rages, particularly for BD1 bromodomains, 100 mM phosphate buffer (pH=6.5, 0.01% Triton X-100 (Sigma, 282103) being added right before assays) was used as the assay buffer. Final Cpd. No. 350 concentration was 1.5 nM for all proteins. Plates were incubated at room temperature for 30 minutes with gentle shaking to assure equilibrium. FP values in millipolarization units (mP) were measured using the Infinite M-1000 plate reader (Tecan U.S., Research Triangle Park, N.C.) in Microfluor 1 96-well, black, round-bottom plates (Thermo Scientific, Waltham, Mass.) at an excitation wavelength of 485 nm and an emission wavelength of 530 nm. Kd values of Cpd. No. 350, which were calculated by fitting the sigmoidal dose-dependent FP increases as a function of protein concentrations using Graphpad Prism 6.0 software (Graphpad Software, San Diego, Calif.), are 2.0, 2.2, 6.5, 0.6, 5.5, and 3.0 nM to BRD2 BD1 and 2, BRD3 BD1 and 2, and BDR4 BD1 and 2, respectively.