Tyrosine-Mediated Static and Dynamic Quenching of a Receptor Tyrosine Kinase Biosensor Reveals Inhibitor Binding Modes and Kinase Conformations

Conformational changes triggered by kinase inhibitors are a major factor driving specificity and efficacy, but few scalable methods exist for differentiating induced conformations and binding modes. Using the receptor tyrosine kinase MET, we show that three classes of inhibitors can be distinguished by their contrasting effects on static and dynamic quenching of a fluorescent dye attached to the activation loop. Quenching is mediated by tyrosine residues on the flexible activation loop, and inhibitor binding induces order in the loop, sequestering the tyrosines and differentially suppressing static and dynamic quenching in a manner that is dependent on the induced structural state. Type I MET inhibitors have a large static and moderate dynamic component, type II inhibitors have only a static component, and active-state-selective inhibitors relieve both components to similar extents. These distinct dequenching signatures allow the straightforward detection of each binding mode by using parallel steady-state and time-resolved fluorescence measurements. We show that this technique can be applied to rapidly assess the effects of resistance mutations on inhibitor binding and can report on the chemical interactions and conformational changes that drive these effects. Conservation of the three activation loop tyrosine residues across many receptor tyrosine kinases suggests that this approach has broad utility.