title: Protein kinase C isozymes and their selectivity towards ruboxistaurin.
abstract: Protein kinase C (PKC) isozymes are an important class of enzymes in cell signaling and as drug targets. They are involved in specific pathways and have selectivity towards certain ligands, despite their high sequence similarities. Ruboxistaurin is a specific inhibitor of PKC-beta. To understand the molecular determinants for the selectivity of ruboxistaurin, we derived the three-dimensional structures of the kinase domains of PKC-alpha, -betaI, and -zeta using homology modeling. Several binding orientations of ruboxistaurin in the binding sites of these PKC catalytic domains were analyzed, and a putative alternative binding site for PKC-zeta was identified in its kinase domain. The calculated free energy of binding correlates well with the IC(50) of the inhibitor against each PKC isozyme. A residue-based energy decomposition analysis attributed the binding free energy to several key residues in the catalytic sites of these enzymes, revealing potential protein-ligand interactions responsible for ligand binding. The contiguous binding site revealed in the catalytic domain of PKC-zeta provides avenues for selective drug design. The details of structural nuances for specific inhibition of PKC isozymes are presented in the context of the three-dimensional structures of this important class of enzymes.
authors.affiliation: Division of Cell and Molecular Biology, Center for Molecular Design and Preformulations, Toronto General Research Institute, University Health Network, Toronto ON M5G 1L7, Canada.
authors.forename: Sishi
authors.initials: S
authors.lastname: Tang
authors.forename: Victor
authors.initials: V
authors.lastname: Xiao
authors.forename: Lianhu
authors.initials: L
authors.lastname: Wei
authors.forename: Catharine I
authors.initials: CI
authors.lastname: Whiteside
authors.forename: Lakshmi P
authors.initials: LP
authors.lastname: Kotra
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D006860:Hydrogen Bonding; D007211:Indoles / Q000737:chemistry / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008301:Maleimides / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D040681:Structural Homology, Protein; D013379:Substrate Specificity; D013816:Thermodynamics
chemical_list: D007211:Indoles; D007527:Isoenzymes; D008301:Maleimides; C099154:ruboxistaurin; D000255:Adenosine Triphosphate; D011493:Protein Kinase C