| Assay Method Information | |
| | Binding Assay ATR (tracer B) |
| Description: | To determine of binding activity of the test compounds, full-length human ATR protein was expressed and purified together with ATRIP as described above. Furthermore, a fluorescently labelled compound (either tracer B as described above) was used as a tracer molecule. Detection of the binding event of the tracer was achieved by time-resolved fluorescence energy transfer (TR-FRET). We used an anti-GST-Terbium antibody (CisBio) that binds to the GST-tag at the N-terminus of ATR-kinase. Excitation of Terbium with 337 nm light results in emission of fluorescent light with 545 nm. In case a tetrameric complex has formed (antiGST-Tb+GST-ATR+Strp2-ATRIP+tracer), part of the energy will be transferred from the Terbium to the fluorophore that itself emits light of 570 nm. Displacement of the fluorescent tracer by a test compound leads to a reduction of the TR-FRET-signal.For the assay 50 nl of a 100-fold concentrated solution of the test compound in DMSO was pipetted into a black low volume 384 well microtiter plate (MTP, Greiner Bio-One, Frickenhausen, Germany). To prepare the ATR-working solution, ATR/ATRIP stock solution was diluted in assay buffer [50 mM HEPES (pH 7.0), 10 mM MgCl2, 1 mM DTT, 0.01% (w/v) Igepal, 0.01% (w/v) BSA] to 4.2 nM protein concentration (concentration may vary from lot to lot of protein preparation). AntiGST-Tb antibody was diluted to 4.2 nM. The ATR-working solution was incubated for 30 min at 22° C. prior to dispensing to pre-form the complex of antiGST-Tb+GST-ATR+ATRIP. Then, 3 μl of the ATR-working solution were added to the test compound and the mixture was incubated for 10 min at 22° C. to allow pre-binding of the test compounds to ATR/ATRIP. Then, 2 μl of a 100 nM solution of either tracer B in assay buffer were added to the ATR-working solution. The resulting mixture was incubated for 30 min at 22° C. The measurement of the TR-FRET signal was performed in a standard HTRF-compatible MTP reader instrument (e.g. BMG Pherastar) by recording the fluorescence emissions at 545 nm and 570 nm after excitation at 337-350 nm. The ratio between emission at 570 nm divided by emission at 545 nm was calculated to give the well ratio. The experimental data (well ratios) were normalised by the following way: positive control contained ATR-working solution plus either tracer B solution (=0% inhibition), the negative control contained all components except GST-ATR/ATRIP (=100% inhibition). Usually the compounds were tested on the same MTP in 11 different concentrations in the range of 20 μM to 0.1 nM (20 μM, 5.9 μM, 1.7 μM, 0.51 μM, 0.15 μM, 44 nM, 13 nM, 3.8 nM, 1.1 nM, 0.33 nM and 0.1 nM). The dilution series were prepared separately before the assay on the level of the 100 fold concentrated solutions in DMSO by serial 1:3.4 dilutions in duplicate values for each concentration. IC50 values were calculated by a 4 parameter fit using standard software (GraphPad prism or equivalent). |
| Affinity data for this assay | |
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