Novel Features of DAG-Activated PKC Isozymes Reveal a Conserved 3-D Architecture

Diacylglycerol (DAG) activates the eight conventional and novel isozymes of protein kinase C (PKC) by binding to their C1 domains. The crystal structure of PKCβII in a partially activated conformation showed how the C1B domain regulates activity by clamping a helix in the C-terminal AGC extension of the kinase domain. Here we show that the global three-dimensional shape of the conventional and novel PKCs is conserved despite differences in the order of the domains in their primary sequences. The membrane translocation phenotypes of mutants in the C1B clamp are consistent across all DAG-activated PKCs, demonstrating conservation of this regulatory interface. We now identify a novel interface that sequesters the C1A domain in PKCβII in a membrane-inaccessible state and we generalize this to all DAG-activated PKCs. In the conventional PKCs, we identify a novel element of their C2 domains that additionally contributes to the stability of the inactive conformation. We demonstrate that the interdomain linkers play important roles in permitting and stabilizing this state. We propose a multi-step activation mechanism in which the sequential and cooperative binding of the regulatory domains to the membrane is coupled to allosteric activation of the kinase domain by DAG and that acquisition of full catalytic activity requires DAG binding to the C1B domain. In light of the conservation of shape and intramolecular architecture, we propose that this mechanism is common to all DAG-activated PKCs.