c-Abl tyrosine kinase and inhibition by the cancer drug imatinib (Gleevec/STI-571)

The search for specific protein kinase inhibitors is an intense area of research because of the potential ford rug development. The small-molecule inhibitor imatinib (Gleevec/STI-571) can specifically inactivate the tyrosine kinase c-Abl, whose normal mechanism of autoinhibition is disrupted in chronic myelogenous leukemia. Crystallographic analysis of c-Abl reveals that imatinib recognizes a distinct inactive conformation of the Abl kinase domain that relies on the mechanism of autoinhibition achieved in the context of a larger fragment of the protein. This mechanism is distinct from that seen in the related Src family kinases, where autoinhibition is achieved through the internal engagement of a C-terminal phosphotyrosine residue by the Src homology 2 domain (SH2) domain. Notably, this phosphotyrosine residue is lacking in c-Abl, where instead autoinhibition is mediated by an interaction between the kinase domain and the N-terminal myristoyl modification. Within the framework of these 2 distinct modes of autoinhibition, the SH3-SH2 unit is structurally conserved between Abl and Src, leading to large conformational differences in their kinase domains. These differences help explain the ability of imatinib to preferentially inhibit Abl over Src.