Activation of tyrosine kinases by mutation of the gatekeeper threonine

Substitution of the active site gatekeeper residue in the BCR-ABL oncoprotein and related kinases is a common mechanism of imanitib resistance but has also been observed in drug-naïve patients. New work suggests that this residue stabilizes a hydrophobic spine that links the N and C kinase lobes, promoting the active conformation, and that adverse mutations at the gatekeeper residue further stabilize the spine. Disruption of the spine would be an attractive new goal in drug development. Protein kinases targeted by small-molecule inhibitors develop resistance through mutation of the 'gatekeeper' threonine residue of the active site. Here we show that the gatekeeper mutation in the cellular forms of c-ABL, c-SRC, platelet-derived growth factor receptor-α and -β, and epidermal growth factor receptor activates the kinase and promotes malignant transformation of BaF3 cells. Structural analysis reveals that a network of hydrophobic interactions—the hydrophobic spine—characteristic of the active kinase conformation is stabilized by the gatekeeper substitution. Substitution of glycine for the residues constituting the spine disrupts the hydrophobic connectivity and inactivates the kinase. Furthermore, a small-molecule inhibitor that maximizes complementarity with the dismantled spine (compound 14) inhibits the gatekeeper mutation of BCR-ABL-T315I. These results demonstrate that mutation of the gatekeeper threonine is a common mechanism of activation for tyrosine kinases and provide structural insights to guide the development of next-generation inhibitors.