Self-reporting fluorescent substrates of protein tyrosine kinases.

A new mechanistic principle by which protein tyrosine kinase substrates fluorescently report the introduction of a phosphate moiety has been developed. NMR was used to establish that tyrosine phosphorylation induces the disruption of pi-pi stacking interactions of the tyrosine moiety with a proximal fluorophore on the peptide substrate. We have demonstrated that (1) the peptide substrates described in this study are useful for a wide variety of different tyrosine kinases, (2) physiological concentrations of ATP can be employed (unlike the standard radioactive ATP kinase assays), thus providing a more realistic assessment of inhibitor potency, and (3) protein kinase self-activation can be observed in real-time.