Role of the Ca2+/phosphatidylserine binding region of the C2 domain in the translocation of protein kinase Cα to the plasma membrane

Signal transduction. via protein kinase C (PKC) is closely regulated by its subcellular localization. To map the molecular determinants mediating the C2 domain-dependent translocation of PKCalpha to the plasma membrane, full-length native protein and several point mutants in the Ca2+/phosphatidylserine-binding site were tagged with green fluorescent protein and transiently expressed in rat basophilic leukemia cells (RBL-2H3). Substitution of several aspartate residues by asparagine completely abolished Ca2+-dependent membrane targeting of PKCalpha. Strikingly, these mutations enabled the mutant proteins to translocate in a diacylglycerol-dependent manner, suggesting that neutralization of charges in the Ca2+ binding region enables the C1 domain to bind diacylglycerol. In addition, it was demonstrated that the protein residues involved in direct interactions with acidic phospholipids play differential and pivotal roles in the membrane targeting of the enzyme. These findings provide new information on how the C2 domain-dependent membrane targeting of PKCalpha occurs in the presence of physiological stimuli.