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| | IRAK4 Kinase Assay |
| Description: | For the assay, 11 different concentrations in the range from 20 μM to 0.073 nM were prepared from a 2 mM DMSO solution of the test substance. 50 nl of the respective solution were pipetted into a black low-volume 384-well microtitre plate (Greiner Bio-One, Frickenhausen, Germany), 2 μl of a solution of IRAK4 in assay buffer [50 mM HEPES pH 7.5, 5 mM MgCl2, 1.0 mM dithiothreitol, 30 μM activated sodium orthovanadate, 0.1% (w/v) of bovine gamma-globulin (BGG) 0.04% (v/v) nonidet-P40 (Sigma)] were added and the mixture was incubated for 15 min to allow prebinding of the substances to the enzyme prior to the kinase reaction. The kinase reaction was then started by addition of 3 μl of a solution of adenosine triphosphate (ATP, 1.67 mM=final concentration in 5 μl of assay volume: 1 mM) and peptide substrate (0.83 μM=final concentration in 5 μl assay volume: 0.5 μM) in assay buffer, and the resulting mixture was incubated at 22° C. for the reaction time of 45 min. The concentration of the IRAK4 was adjusted to the respective activity of the enzyme and set such that the assay was carried out in the linear range. Typical concentrations were in the order of about 0.2 nM. The reaction was stopped by addition of 5 μl of a solution of TR-FRET detection reagents [0.1 μM streptavidin-XL665 (Cisbio Bioassays; France, catalogue No. 610SAXLG)] and 1.5 nM anti-phosphoserine antibody [Merck Millipore, STK Antibody , catalogue No. 35-002] and 0.6 nM LANCE EU-W1024-labelled anti-mouse-IgG antibody (Perkin-Elmer, product No. AD0077; alternatively, it is possible to use a terbium cryptate-labelled anti-mouse-IgG antibody from Cisbio Bioassays) in aqueous EDTA solution (100 mM EDTA, 0.4% [w/v] bovine serum albumin [BSA] in 25 mM HEPES pH 7.5).The resulting mixture was incubated at 22° C. for 1 h to allow formation of a complex of the biotinylated phosphorylated substrate and the detection reagents. The amount of the phosphorylated substrate was then evaluated by measuring the resonance energy transfer from europium chelate-labelled anti-mouse-IgG antibody to streptavidin-XL665. To this end, the fluorescence emissions at 620 nm and 665 nm were measured after excitation at 350 nm in a TR-FRET measuring instrument, for example a Rubystar (BMG Labtechnologies, Offenburg, Germany) or a Viewlux (Perkin-Elmer). The ratio of the emissions at 665 nm and 622 nm was taken as a measure of the amount of phosphorylated substrate. The data were normalized (enzyme reaction without test substance=0% inhibition; all other assay components but no enzyme=100% inhibition). Typically, the test substances were tested on the same microtitre plates at 11 different concentrations in the range from 20 μM to 0.073 nM (20 μM, 5.7 μM, 1.6 μM, 0.47 μM, 0.13 μM, 38 nM, 11 nM, 3.1 nM, 0.89 nM, 0.25 nM and 0.073 nM). The dilution series were prepared prior to the assay (2 mM to 7.3 nM in 100% DMSO) by serial dilutions. The IC50 values were calculated by a 4-parameter fit. |
| Affinity data for this assay | |
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