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Assay Method Information

Assay Name:  Time-Resolved Fluorescence Resonance energy Transfer (TR-FRET) Assay
Description:  For this purpose, a time-resolved fluorescence resonance energy transfer (TR-FRET) assay was used, which measures the binding between N-terminally His6-tagged BRD4(1) (amino acids 44-168) and a synthetic acetylated histone H4 (Ac-H4) peptide with sequence GRGK(Ac)GGK(Ac)GLGK(Ac)GGAK(Ac)RHGSGSK-biotin. The recombinant BRD4 protein produced in-house according to Filippakopoulos et al., Cell, 2012, 149:214-231 was expressed in E. coli and purified by means of (Ni-NTA) affinity and (Sephadex G-75) size exclusion chromatography. The Ac-H4 peptide can be purchased, for example, from Biosyntan (Berlin, Germany).In the assay, typically 11 different concentrations of each substance (0.1 nM, 0.33 nM, 1.1 nM, 3.8 nM, 13 nM, 44 nM, 0.15 μM, 0.51 μM, 1.7 μM, 5.9 μM and 20 μM) were analysed as duplicates on the same microtitre plate. For this purpose, 100-fold concentrated solutions in DMSO were prepared by serial dilutions (1:3.4) of a 2 mM stock solution into a clear, 384-well microtitre plate (Greiner Bio-One, Frickenhausen, Germany). From this, 50 nl were transferred into a black test plate (Greiner Bio-One, Frickenhausen, Germany). The test was started by the addition of 2 μl of a BRD4 solution of 2.5 times the concentration (final concentration typically 10 to 50 nM in the 5 μl of reaction volume) in aqueous assay buffer [50 mM HEPES pH 7.5, 50 mM sodium chloride (NaCl), 0.25 mM CHAPS and 0.05% bovine serum albumin (BSA)] to the substances in the test plate. This was followed by a 10-minute incubation step at 22 C. for the pre-equilibration of putative complexes between BRD4 and the substances. Subsequently, 3 μl of a solution of 1.67 times the concentration (in assay buffer) consisting of Ac-H4 peptide (83.5 nM) and TR-FRET detection reagents [16.7 nM anti-6His-XL665 and 3.34 nM streptavidin cryptate (both from Cisbio Bioassays, Codolet, France), and 668 mM potassium fluoride (KF)] were added.
Affinity data for this assay
 

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Last update November 1, 2007
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