Membrane translocation of novel protein kinase Cs is regulated by phosphorylation of the C2 domain

Ca2+-independent or novel protein kinase Cs (nPKCs) contain an N-terminal C 2 domain of unknown function. Removal of the C2 domain of the Aplysia nPKC Apl II allows activation of the enzyme at lower concentrations of phosphati dylserine, suggesting an inhibitory role far the C2 domain in enzyme activa tion. However, the mechanism for Ca domain-mediated inhibition is not known . Mapping of the autophosphorylation sites for protein kinase C (PRC) ApI I I reveals four phosphopeptides in the regulatory domain of PRC ApI II, two of which are in the C2 domain at serine 2 and serine 36. Unlike most PKC au tophosphorylation sites, these serines could be phosphorylated in trans. In terestingly, phosphorylation of serine 36 increased binding of the C2 domai n to phosphatidylserine membranes in vitro. In cells, PRC Apl II phosphoryl ation at serine 36 was increased by PKC activators, and PKC phosphorylated at this position translocated more efficiently to membranes. Moreover, muta tion of serine 36 to alanine significantly reduced membrane translocation o f PKC Apl II. We suggest that translocation of nPKCs is regulated by phosph orylation of the C2 domain.