Increased membrane affinity of the C1 domain of protein kinase Cδ compensates for the lack of involvement of its C2 domain in membrane recruitment

Protein kinase C (PKC) family members are allosterically activated following membrane recruitment by specific membrane-targeting modules. Conventional PKC isozymes are recruited to membranes by two such modules: a C1 domain, which binds diacylglycerol (DAG), and a C2 domain, which is a Ca2+-triggered phospholipid-binding module. In contrast, novel PKC isozymes respond only to DAG, despite the presence of a C2 domain. Here, we address the molecular mechanism of membrane recruitment of the novel isozyme PKC delta. We show that PKC delta and a conventional isozyme, PKC beta II, bind membranes with comparable affinities. However, dissection of the contribution of individual domains to this binding revealed that, although the C2 domain is a major determinant in driving the interaction of PKC beta II with membranes, the C2 domain of PKC delta does not bind membranes. Instead, the C1B domain is the determinant that drives the interaction of PKC delta with membranes. The C2 domain also does not play any detectable role in the activity or subcellular location of PKC delta in cells; in vivo imaging studies revealed that deletion of the C2 domain does not affect the stimulus-dependent translocation or activity of PKC delta. Thus, the increased affinity of the C1 domain of PKC delta allows this isozyme to respond to DAG alone, whereas conventional PKC isozymes require the coordinated action of Ca2+ binding to the C2 domain and DAG binding to the C1 domain for activation.