New Insights into the Molecular Structure of the Agonists Binding Site of Protein Kinase C by Pseudoreceptor Modeling

Abstract

Protein kinase C (PKC) comprises a family of isoenzymes with serine/threonine kinase activity similar in molecular size, structure and mechanism of activation. This enzyme family is an important part of one of the major signal transduction pathways regulating many intracellular processes such as modulation of gene expression, cell proliferation and differentiation. PKC was identified as the major cellular receptor for skin tumor promoting phorbol esters and certain other compounds exhibiting skin tumor promoting bioactivity. Moreover, PKC is a target for molecules with antineoplastic activity like bryostatin. Thus by various investigators it is considered as a potential target for discovery and development of new anticancer drugs. On the other hand for PKC so far no potent and isoenzyme selective activators or inhibitors are known, and a 3-D structure of the enzyme is not available. Therefore a new technique of molecular modeling was investigated to design the agonist binding site of PKC: ‘Pseudoreceptor modeling’. It is a comprehensive strategy in the design of potent, selective and novel ligands for unknown receptors (Vedani et al., 1993). The new approach is focused on the binding site of the receptor and allows the construction of hypothetical 3-D-models of binding pockets using the directionality of receptor-ligand interactions (hydrogen bonds, metal-ligand interaction, hydrophobic interactions). In the investigation described an ensemble of six ligands, binding all specifically to the regulatory domain of the enzyme and representing together a pharmacophore model for activation of PKC, was successfully used. The pseudoreceptor model of PKC will be presented. It may be used as a surrogate of the agonist binding site of PKC to guide the synthesis of new and selective PKC-agonists allowing further investigation of PKC-isoforms in the signal transduction pathway. In addition it may be of assistance in the development for new antineoplastic drugs.