Assay Method Information

Assay Name:  CDK2/Cyclin E1 Mobility Shift Assay
Description:  The purpose of the CDK2/Cyclin E1 assay is to evaluate the inhibition (% inhibition, Kiapp and Ki values) of small molecule inhibitors by using a fluorescence-based microfluidic mobility shift assay. CDK2/Cyclin E1 catalyzes the production of ADP from ATP that accompanies the phosphoryl transfer to the substrate peptide FL-Peptide-18 (5-FAM-QSPKKG-CONH2) (SEQ ID NO:1). (CPC Scientific, Sunnyvale, Calif.). The mobility shift assay electrophoretically separates the fluorescently labeled peptides (substrate and phosphorylated product) following the kinase reaction. Both substrate and product are measured and the ratio of these values is used to generate % conversion of substrate to product by the LabChip EZ Reader. Wild-type full length CDK2/wild-type full length Cyclin E1 enzyme complex was produced in-house (baculoviral expression, LJIC-2080/LJIC-2103) and phosphorylated by CDK7/Cyclin H1/Mat1 enzyme complex with CDK2:CDK7 ratio of 50:1 (concentration mg/mL) in the presence of 10 mM MgCl2 and 5 mM ATP at room temperature for one hour. Typical reaction solutions (50 μL final reaction volume) contained 2% DMSO (±inhibitor), 4 mM MgCl2, 1 mM DTT, 150 μM ATP (ATP Km=67.4 μM), 0.005% Tween-20, 3 μM FL-Peptide-18, and 0.36 nM (catalytically competent active site) phosphorylated wild-type full length CDK2/Cyclin E1 enzyme complex in 25 mM HEPES buffer at pH 7.15. The assay was initiated with the addition of ATP, following a fifteen minutes pre-incubation of enzyme and inhibitor at room temperature in the reaction mixture. The reaction was stopped after 45 minutes at room temperature by the addition of 50 μL of 80 mM EDTA, pH 7.5. The Ki value was determined from the fit of the data to the Morrison tight-binding competitive inhibition equation with the enzyme concentration as a variable.
Affinity data for this assay

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