Structure of the C2 domain from novel protein kinase Cϵ. A membrane binding model for Ca2+-independent C2 domains

Protein kinase Cϵ (PKCϵ) is a member of the novel PKCs which are activated by acidic phospholipids, diacylglycerol and phorbol esters, but lack the calcium dependence of classical PKC isotypes. The crystal structures of the C2 domain of PKCϵ, crystallized both in the absence and in the presence of the two acidic phospholipids, 1,2-dicaproyl-sn-phosphatidyl-l-serine (DCPS) and 1,2-dicaproyl-sn-phosphatidic acid (DCPA), have now been determined at 2.1, 1.7 and 2.8 Å resolution, respectively. The central feature of the PKCϵ-C2 domain structure is an eight-stranded, antiparallel, β-sandwich with a type II topology similar to that of the C2 domains from phospholipase C and from novel PKCδ. Despite the similar topology, important differences are found between the structures of C2 domains from PKCs δ and ϵ, suggesting they be considered as different PKC subclasses. Site-directed mutagenesis experiments and structural changes in the PKCϵ-C2 domain from crystals with DCPS or DCPA indicate, though phospholipids were not visible in these structures, that loops joining strands β1-β2 and β5-β6 participate in the binding to anionic membranes. The different behavior in membrane-binding and activation between PKCϵ and classical PKCs appears to originate in localized structural changes, which include a major reorganization of the region corresponding to the calcium binding pocket in classical PKCs. A mechanism is proposed for the interaction of the PKCϵ-C2 domain with model membranes that retains basic features of the docking of C2 domains from classical, calcium-dependent, PKCs.