FGFR kinase isoform and activation state modulate ATPase activity

Fibroblast growth factor (FGF) binding to FGF receptor (FGFR) induces trans-autophosphorylation of activation loop tyrosine residues within the receptor's intracellular kinase domain, thereby activating the receptor and promoting downstream substrate phosphorylation. Here, using activity assays and ³¹P NMR spectroscopy on the FGFR kinase domain, we show that phosphorylation of activation loop tyrosine residues not only enhances kinase activity but also increases the rate of ATP hydrolysis by 33-fold. This ATPase activity varies among FGFR kinase isoforms, with a 5.4-fold difference between FGFR2 and FGFR3 kinases. Conversion of ATP to ADP in phosphorylation assays also promotes the reverse phosphorylation reaction, which involves phosphoryl group transfer from phosphotyrosine to ADP to regenerate ATP. Based on these observations, we hypothesize that ATPase activity occurs in cells and may decrease the local ATP/ADP ratio surrounding FGFR. Such a mechanism would reduce the favorability of phosphorylation and may promote signal termination through reverse phosphorylation.