PHOSPHATIDYL-L-SERINE IS NECESSARY FOR PROTEIN-KINASE CS HIGH-AFFINITY INTERACTION WITH DIACYLGLYCEROL-CONTAINING MEMBRANES

The contributions of phospholipid headgroup structure, diacylglycerol, and Ca2+ in regulating the interaction of protein kinase C beta II wi th membranes or detergent/lipid mixed micelles were examined. Binding measurements revealed that, in the absence of diacylglycerol, protein kinase C displays no significant selectivity for headgroup structure o ther than charge: the enzyme binds with equal affinity to phosphatidyl -L-serine, phosphatidyl-D-serine, and other monoanionic lipids such as phosphatidylglycerol. In contrast, selectivity for headgroup occurs i n the presence of diacylglycerol. This second messenger increases the affinity of protein kinase C for phosphatidyl-L-serine-containing memb ranes or micelles by 2 orders of magnitude, but has only moderate effe cts on the affinity of protein kinase C for surfaces containing other anionic lipids. Ca2+ does not affect the diacylglycerol-mediated incre ase in protein kinase C's affinity for phosphatidylserine, but does in crease the enzyme's affinity for acidic phospholipids. Lastly, ionic s trength studies reveal that electrostatic interactions are the primary driving force in the interaction of protein kinase C with membranes. In the absence of either diacylglycerol or phosphatidylserine, these i nteractions are sufficiently weak that little binding occurs at physio logical ionic strength; thus, protein kinase C is unlikely to transloc ate to the plasma membranes in the absence of diacylglycerol, even if intracellular Ca2+ levels are high. Our data reveal that, although the re is no specificity for binding acidic lipids in the absence of diacy lglycerol, specific structural elements of the L-serine headgroup are required for the high-affinity binding of protein kinase C to diacylgl ycerol-containing membranes.