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.