LIPID STRUCTURE AND NOT MEMBRANE-STRUCTURE IS THE MAJOR DETERMINANT IN THE REGULATION OF PROTEIN-KINASE-C BY PHOSPHATIDYLSERINE

This study addresses the molecular basis for protein kinase C's specif ic activation by phosphatidylserine. Specifically, we ask whether prot ein kinase C's phospholipid specificity arises from specific protein/l ipid interactions or whether it arises from unique membrane-structurin g properties of phosphatidylserine. We measured the interaction of pro tein kinase C beta II to membranes that differed only in being enantio mers to one another: physical properties such as acyl chain compositio n, membrane fluidity, surface curvature, microdomains, headgroup packi ng, and H-bonding with water were identical. Binding and activity meas urements reveal that protein kinase C specifically recognizes 1,2-sn-p hosphatidyl-L-serine, independently of membrane structure. High-affini ty binding and activation are abolished in the presence of enantiomeri c membranes containing 2,3-sn-phosphatidyl-L-serine, 2,3-sn-diacylglyc erol, and 2,3-sn-phosphatidylcholine. Our data also show that the ster eoselectivity for 1,2-sn-diacylglycerol is not absolute; 2,3-sn-diacyl glycerol modestly increases the membrane affinity of protein kinase C provided that 1,2-sn-phosphatidyl-L-serine is present. We also find th at the stereochemistry of the bulk phospholipid, in this case phosphat idylcholine, has no significant influence on protein kinase C's membra ne interaction. These data reveal that specific molecular determinants on protein kinase C stereospecifically recognize structural determina nts of phosphatidylserine.