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Assay Method Information

Assay Name:  Time Resolved-Fluorescence Energy Transfer (TR-FRET) Assay
Description:  Compounds were profiled for activity against human FABP4 (huFABP4) and/or human FABP5 (huFABP5) in Terbium (Tb) time resolved-fluorescence energy transfer (TR-FRET) assays monitoring the direct binding of Bodipy labeled fatty acid to His6 tagged FABP proteins (huFABP4 was expressed in house in E. Coli and purified, huFABP5 was purchased from Cayman Chemical Co., cat.no. 10010364), bound to Terbium labeled anti His6 tag antibody. Assay read-outs reflected energy transfer, upon binding of the ligand to the FABP protein, from the Terbium donor molecule to the acceptor Bodipy moiety. Final ligand concentration (125 nM) approximated the Kd for each protein.Stock DMSO solutions (1.8 mM) of compounds were serially diluted 3-fold for ten concentrations with 100% DMSO (50 μM to 0.003 μM final compound concentration). 1 μl of these compound dilutions and 1 μl of Bodipy labeled fatty acid 4.5 μM in 100% DMSO (Bodipy FL C11, cat. no. D3862, Invitrogen) were sequentially pipetted in wells of 384-well black polypropylene plates (Thermo Matrix cat. no. 4344). FABP4 or FABP5 protein was then added (28 μl of 64 nM protein in 25 mM Tris pH 7.5, 0.4 mg/ml γ-globulin, 1 mM DTT, 0.012% NP40, final protein concentration: 50 nM). Assay blanks contained ligand, but no protein. Neutral controls contained ligand, but no compound. After adding the detection reagent (Tb antiHis6 antibody, Columbia Biosciences, TB-110, 6 μl of a 24 nM Ab solution in 25 mM Tris pH 7.5, 0.4 mg/ml γ-globulin, final Tb antiHis6 Ab concentration: 4 nM), plates were spun one minute at 1000 rpm. Following an incubation at room temperature with shaking for 30 minutes, plates were read using an Envision reader (Perkin Elmer, Extinction wavelength: 340 nm, Emission: 490 nm and 520 nm, time delay: 100 μs; time window: 200 μs, 50 flashes).Final assay conditions were: 50 nM FABP protein, 125 nM Bodipy labeled fatty acid, 0.009% (vol/vol) NP40, 5.5% (vol/vol) DMSO in a total final assay volume of 36 μl. The assay was performed in triplicate.
Affinity data for this assay
 

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Last update November 1, 2007
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