Evidence for a regulatory binding site for arginine-rich peptides on protein kinase C

The peptides N-biotinyl-RRRCLRRL and N-biotinyl-RKRCLRRL covalently modify protein kinase C (PKC) through reaction of the Cys sulfhydryl group with the active site of the enzyme. The labeling of PKC occurs only in the presence of the cofactors phosphatidylserine, diacylglycerol, and Ca2+ but not in their absence. Low concentrations of the Arg-rich substrate, R4YGSR6Y greatly increase the extent of the reaction of these biotinylated peptides with PKC in the presence of lipid cofactors but in the absence of calcium. This effect can be observed at 50 nM R4YGSR6Y and suggests the presence of a high-affinity binding site for Arg-rich peptides which is separate from the active site but which enhances accessibility of the active site. The study also demonstrates the utility of the biotinylated peptides as active site labels which can detect the conformational change accompanying the activation of PKC.