Limited proteolysis of protein kinase C subspecies by calpain: stimulation by basic polypeptides

Limited proteolysis of Protein Kinase C (PKC) subspecies by Ca(2+)-dependent neutral protease II (calpain II) was remarkably stimulated by the presence of basic polypeptides, such as H1 histone, protamine, poly-L-arginine, and poly-L-lysine. The stimulatory effect of basic polypeptides was observed for proteolysis of the active form of PKC which was associated with diacylglycerol and phospholipid. The inactive form of PKC was far less susceptible to proteolysis, either in the presence or absence of the basic polypeptides. The basic polypeptides did not appear to interact with calpain II, but caused a conformational change in PKC to make the kinase molecule more susceptible to proteolysis. The relative rates of cleavage of the active form of types I (gamma), II (beta), and III (alpha) PKC by calpain II in the absence and presence of basic polypeptides were 100:48:23 and 100:100:50, respectively. Available evidence suggests that, like calpain I, calpain II may also contribute to the down-regulation or depletion of PKC.