| Assay Method Information | |
| | 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 a fluorescein isothiocyanate-labeled BH3 peptide derived from Bak (FITC-AHx-GQVGRQLAIIGDDINR-NH2) that was purchased from GenScript (Piscataway, N.J.) at >95% purity and used without further purification. 10 nM FITC-Bak peptide and 14 nM recombinant Mcl-1 (residues 172-327) were added to assay buffer (3 mM dithiothreitol, 50 mM NaCl, 20 mM Tris, pH 7.5). For selectivity assays, 40 nM Bcl-2 (residues 1-207A96T,G110R, 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. 2.5 uL compound is added to 47.5 uL of assay buffer containing FITC-Bak and protein, for a final DMSO concentration of 5% and a top concentration of 20 uM. A FITC-Bak 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). 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). IC50 is converted to a binding dissociation constant (Ki value) according to the formula of Wang Z. FEBS Lett (1996) 3, 245:K i =[I] 50/([L] 50 /K d +[P] 0 /K d+1)where [I]50 is the concentration of the free inhibitor at 50% inhibition, [L]50 is the concentration of the free labeled ligand at 50% inhibition, [P]0 is the concentration of the free protein at 0% inhibition, Kd represents the dissociation constant of the FITC peptide probe. |
| Affinity data for this assay | |
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