Structural basis for selective inhibition of Src family kinases by PP1

Background: Small-molecule inhibitors that can target individual kinases ar e powerful tools for use in signal transduction research. It is difficult t o find such compounds because of the enormous number of protein kinases and the highly conserved nature of their catalytic domains. Recently, a novel, potent, Src family selective tyrosine kinase inhibitor was reported (PP1). Here, we study the structural basis for this inhibitor's specificity for S rc family kinases. Results: A single residue corresponding to Ile338 (v-Src numbering; Thr338 in c-Src) in Src family tyrosine kinases largely controls PP1's ability to inhibit protein kinases. Mutation of Ile338 to a larger residue such as met hionine or phenylalanine in v-Src makes this inhibitor less potent. Convers ely, mutation of Ile338 to alanine or glycine increases PP1's potency. PP1 can inhibit Ser/Thr kinases if the residue corresponding to Ile338 in v-Src is mutated to glycine. We have accurately predicted several non-Src family kinases that are moderately (IC50 similar to 1 mu M) inhibited by PP1, inc luding c-Abl and the MAP kinase p38. Conclusions: Our mutagenesis studies of the ATP-binding site in both tyrosi ne kinases and Ser/Thr kinases explain why PP1 is a specific inhibitor of S rc family tyrosine kinases. Determination of the structural basis of inhibi tor specificity will aid in the design of more potent and more selective pr otein kinase inhibitors. The ability to desensitize a particular kinase to PP1 inhibition of residue 338 or conversely to sensitize a kinase to PP1 in hibition by mutation should provide a useful basis for chemical genetic stu dies of kinase signal transduction.