Assay Report Card

ID: ALA3889118

Type: Binding

Description: Homogeneous Time Resolved Fluorescence Resonance Energy Transfer (TR-FRET) Assay: Binding of the two tandem bromodomains, BRD4-1 and BRD4-2, to an acetylated histone H4 peptide was measured using a homogeneous time resolved fluorescence resonance energy transfer (TR-FRET) assay. The synthetic peptide containing amino acids 1-18 of histone H4 was acetylated at lysine 5, 8, 12, 16 and conjugated to biotin (SGRGACKGGACKGLGACKGGAACKRH-GSGSK-biotin[SEQ ID NO:1]) was purchased from Millipore. BRD4-1 and BRD4-2 were expressed and purified from Escherichia coli as N-terminal His6-tagged proteins. An XL665 labeled anti-His antibody (Cisbio) was used to specifically bind BRD4 and a cryptate labeled streptavidin protein was used because it specifically recognized the biotinylated H4 peptide. Binding of BRD4 to the peptide resulted in an increase in FRET signal whereas disruption of this protein-peptide interaction with a small molecule inhibitor resulted in a decrease in FRET signal. Assays were performed in 50 mM Hepes (pH 7.5), 150 mM NaCl, 0.1 mg/ml BSA, 0.01% (v/v) Brij, 0.5% (v/v) DMSO and 200 nM H4 peptide at the following concentrations for each BRD4 isoform: 60 nM BRD4-1 and 120 nM BRD4-2. After an assay reaction time of 60 minutes at 25° C., binding was measured with 2 nM crytptate labeled streptavidin and 10 nM anti-His-XL665 antibody. TR-FRET signal was detected on an Envision plate reader (Ex: 320 nm; Em: 615/665 nm; 100 As delay and 200 μs read window). Data were normalized based on a positive (2 μM I-BET) and negative (DMSO) controls and IC50values were calculated from the fit of the dose-response curves to a four-parameter equation. All IC50 values represent geometric mean values of a minimum of four determinations.