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Assay Method Information

Assay Name:  Bak Peptide Binding Assay
Description:  Compound affinity was measured using a fluorescence polarization anisotropy competition assay. Anisotropy measurements were carried out in 384-well, black, flat-bottom plates (Greiner Bio-one, Monroe, N.C., USA). The assay was run using either a fluorescein isothiocyanate-labeled BH3 peptide derived from Bak (FITC-AHx-GQVGRQLAIIGDDINR-NH2) or a fluorescein isothiocyanate-labeled BH3 peptide derived from Bim (FITC-AHx-EARIAQELRRIGDEFNETYTR NH2) that were purchased from GenScript (Piscataway, N.J.) at >95% purity and used without further purification. 10 nM FITC-Bak peptide and 15 nM recombinant Mcl-1 (residues 172-327) were added to assay buffer (3 mM dithiothreitol, 50 mM NaCl, 20 mM Tris, pH 7.5). The Bim based assay was run with 1 nM FITC-Bim peptide and 1.5 nM recombinant Mcl-1 (residues 172-327) added to assay buffer (20 mM TRIS pH 7.5, 50 mM NaCl, 3 mM DTT, 0.01% CHAPS). For selectivity assays, 40 nM Bcl-2 (residues 1-207A96T,G11OR, Δ35-91, replaced with Bcl-xL35-50) or 4 nM Bcl-xL (residues 1-209, loop 45-86 deleted) were incubated with 10 nM FITC-Bak in assay buffer.Compounds are diluted in DMSO in a 10-point, 3-fold serial dilution scheme. For the FITC -BAK assay 2.5 uL compound is added to 47.5 μL of assay buffer containing FITC-Bak and protein, for a final DMSO concentration of 5% and a top concentration of 20 μM. A FITC-Bak peptide alone (100% inhibition) and peptide plus protein (0% inhibition) control is included on each assay plate. For the FITC -Bim assay, compound is added to 40 uL of assay buffer containing protein, 15 minutes prior to addition of 10 μL of the FITC-Bim peptide, for a final DMSO concentration of 0.165% and a top concentration of 200 nM. A FITC-Bim peptide alone (100% inhibition) and peptide plus protein (0% inhibition) control is included on each assay plate. The plate was mixed and incubated for 90 minutes at room temperature. Anisotropy is measured at excitation wavelength 480 nm and emission wavelength 535 nm using an EnVision Multi-label plate reader (PerkinElmer, Wellesley, Mass., USA) or a BioTek Cytation 3 (BioTek, Winooski, Vt., USA). Fluorescence anisotropy is plotted against compound concentration to generate an IC50 (inhibitor concentration at which 50% of bound peptide is displaced) by fitting the data to a 4-parameter logistic model using XLFit software (Guildford, Surrey, UK).
Affinity data for this assay
 

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Last update November 1, 2007
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