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Assay Method Information

Assay Name:  Biochemical Assay for mTOR
Description:  TR-FRET assays for protein kinases uses a long-lifetime lanthanide Terbium or Europium chelates as the donor species which overcome interference by compound autofluorescence or light scatter from precipitated compounds, by introducing a delay after excitation by a flashlamp excitation source. Results are often expressed as a ratio of the intensities of the acceptor and donor fluorophores. The ratiometric nature of such a value corrects for differences in assay volumes between wells, as well as corrects for quenching effects due to colored compounds.Binding Assays are based on the binding and displacement of an Alexa Fluor® 647-labeled, ATP-competitive kinase inhibitors to the kinase of interest. Invitrogen's “Kinase Tracers” have been developed to address a wide range of kinase targets and are based on ATP-competitive kinase inhibitors, making them suitable for detection of any compounds that bind to the ATP site or to an allosteric site altering the conformation of the ATP site. Inhibitors that bind the ATP site include both Type I kinase inhibitors, which bind solely to the ATP site, and Type II inhibitors (e.g., Gleevec/Imatinib, Sorafenib, BIRB-796), which bind to both the ATP site and a hydrophobic site exposed in the DFG-out (non-active) conformation. Type III inhibitors are compounds that do not compete with ATP are loosely referred to as allosteric inhibitors. A study of 15 diverse Type III inhibitors demonstrated that all but one compound was detected in the binding assay with equivalent potency to activity assays. The sole exception was a substrate-competitive compound, and thus not a true allosteric inhibitor.In contrast to most fluorescence-based kinase activity assays, LanthaScreen® Eu3+ Kinase Binding Assays can be read continuously, which facilitates evaluation of compounds with slow binding kinetics. Also, unlike most activity assays, binding assays can be performed using either active or non-activated kinase preparations, which enables characterization of compounds that bind preferentially to non-activated kinases, such as Gleevec®/imatinib and some allosteric inhibitors.In the Lanthascreen™ kinase binding assay, the donor (Eu3+-anti-GST antibody) is excited at 340 nm and will transfer its energy to the acceptor (Alexa Fluor® 647-labeled ATP-competitive kinase inhibitor=Tracer-314). The emission from the Tracer-314 (Alexa Fluor® 647 inhibitor) can be monitored with a filter centered at 665 nm because it is located between the emission peaks of the donor, which is measured at 615/620 nm. The binding of both, the Tracer-314 and Eu3+-anti-GST antibody, to the kinase results in a high degree of FRET from the Eu3+-donor fluorophore to the Alexa-Fluor 647-acceptor fluorophore on the Tracer-314. Binding of an inhibitor to the kinase competes for binding with the tracer, resulting in a loss of FRET.50 nL of compound dilutions were dispensed onto white 384-well small volume polystyrene plate as described in section 2.2. Then 5 μL of GST-mTOR and Europium-anti-GST antibody followed by 5 μL of tracer-314 (final assay volume 10 μL) are incubated at RT. The standard reaction buffer for the Lanthascreen™ kinase binding assay contained 50 mM HEPES pH 7.5, 5 mM MgCl2, 1 mM EGTA, 0.01% Pluronic F-127. Plates are read 60 mins later in a Synergy2 reader using an integration time of 0.2 microseconds and a delay of 0.1 microseconds.To calculate the emission ratio, the signal emitted at 665 nm from the acceptor (Alexa Fluor® 647-labeled Tracer-314) is divided by the signal emitted at 620 nm from the donor (Eu3+ anti-GST antibody)Control for the 0% inhibition was given by the solvent vehicle of the compounds (90% DMSO in H2O). Control for the relative 100% inhibition was performed by adding 10 μM in the mix containing GST-mTOR and Europium anti-GST antibody. An additional control for the absolute 0% inhibition is given by Eu3+ anti-GST antibody without GST-mTOR.
Affinity data for this assay
 

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Last update November 1, 2007
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