Structure of the catalytic domain of human protein kinase C β II complexed with a bisindolylmaleimide inhibitor

The conventional protein kinase C isoform, PKC beta II, is a signaling kinase activated during the hyperglycemic state and has been associated with the development of microvascular abnormalities associated with diabetes. PKC beta II, therefore, has been identified as a therapeutic target where inhibitors of its kinase activity are being pursued for treatment of microvascular-related diabetic complications. In this report, we describe the crystal structure of the catalytic domain of PKC beta II complexed with an inhibitor at 2.6 angstrom resolution. The kinase domain of PKC beta II was cleaved and purified from full-length PKC beta II expressed in baculovirus-infected insect cells. The overall kinase domain structure follows the classical bilobal fold and is in its fully activated conformation with three well-defined phosphorylated residues: Thr-500, Thr-641, and Ser-660. Different from the crystal structures of nonconventional PKC isoforms, the C-terminus of the PKC beta II catalytic domain is almost fully ordered and features a novel R helix in the turn motif. An ATP-competitive inhibitor, 2-methyl-1H-indol-3-yl-BIM-1, was crystallized with the PKC beta II catalytic domain as a dimer of two enzyme-inhibitor complexes. The bound inhibitor adopts a nonplanar conformation in the ATP-binding site, with the kinase domain taking on an intermediate, open conformation. This PKC beta II-inhibitor complex represents the first structural description of any conventional PKC kinase domain. Given the pathogenic role of PKC beta II in the development of diabetic complications, this structure can serve as a template for the rational design of inhibitors as potential therapeutic agents.