The active site substrate specificity of protein kinase C

The active site substrate specificity of protein kinase C (PKC) has been evaluated. Like the cAMP-dependent protein kinase (PKA), PKC will efficiently phosphorylate achiral residues attached to an active site-directed peptide. In contrast, PKC exhibits behavior that is dramatically different from PKA with respect to the phosphorylation of alpha-substituted alcohols. Although PKA will only phosphorylate residues that contain the same stereochemistry as that found in L-serine, PKC will phosphorylate alpha-configurational isomers that correspond to both the L- and D-stereoisomers. The possible structural basis for the "dual specificity" of PKC is explored. In an analogous vein, although beta-substituted alcohols that serve as PKA substrates must contain the same stereochemistry as that present in L-threonine, PKC will phosphorylate configurational isomers which correspond to both L-threonine and L-allo-threonine. The implications of these observations with respect to protein kinase inhibitor design are discussed.