CRYSTAL-STRUCTURES OF CATALYTIC SUBUNIT OF CAMP-DEPENDENT PROTEIN-KINASE IN COMPLEX WITH ISOQUINOLINESULFONYL PROTEIN-KINASE INHIBITORS H7,H8, AND H89 - STRUCTURAL IMPLICATIONS FOR SELECTIVITY

The discovery of several hundred different protein kinases involved in highly diverse cellular signaling pathways is in stark contrast to th e much smaller number of known modulators of cell signaling, Of these, the H series protein kinase inhibitors (1-(5-isoquinolinesulfonyl)-2- methylpiperazine (H7), -[2-(methylamino)-ethyl]-5-isoquinolinesulfonam ide (H8) omo-cinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89)) are frequently used to block signaling pathways in studies of cellular re gulation. To elucidate inhibition mechanisms at atomic resolution and to enable structure-based drug design of potential therapeutic modulat ors of signaling pathways, we determined the crystal structures of cor responding complexes with the cAPK catalytic subunit. Complexes with H 7 and H8 (2.2 Angstrom) and with H89 (2.3 Angstrom) define the binding mode of the isoquinoline-sulfonamide derivatives in the ATP-binding s ite while demonstrating effects of ligand-induced structural change. S pecific interactions between the enzyme and the inhibitors include the isoquinoline ring nitrogen ligating to backbone amide of Val-123 and an inhibitor side chain amide bonding to the backbone carbonyl of Glu- 170. The conservation of the ATP-binding site of protein kinases allow s evaluation of factors governing general selectivity of these inhibit ors among kinases. These results should assist efforts in the design o f protein kinase inhibitors with specific properties.