Lipid Structure and Not Membrane Structure Is the Major Determinant in the Regulation of Protein Kinase C by Phosphatidylserine

Abstract

This study addresses the molecular basis for protein kinase C's specific activation by phosphatidylserine. Specifically, we ask whether protein kinase C's phospholipid specificity arises from specific protein/lipid interactions or whether it arises from unique membrane-structuring properties of phosphatidylserine. We measured the interaction of protein kinase C βII to membranes that differed only in being enantiomers to one another: physical properties such as acyl chain composition, membrane fluidity, surface curvature, microdomains, headgroup packing, and H-bonding with water were identical. Binding and activity measurements reveal that protein kinase C specifically recognizes 1,2-sn-phosphatidyl-l-serine, independently of membrane structure. High-affinity binding and activation are abolished in the presence of enantiomeric membranes containing 2,3-sn-phosphatidyl-l-serine, 2,3-sn-diacylglycerol, and 2,3-sn-phosphatidylcholine. Our data also show that the stereoselectivity for 1,2-sn-diacylglycerol is not absolute; 2,3-sn-diacylglycerol modestly increases the membrane affinity of protein kinase C provided that 1,2-sn-phosphatidyl-l-serine is present. We also find that the stereochemistry of the bulk phospholipid, in this case phosphatidylcholine, has no significant influence on protein kinase C's membrane interaction. These data reveal that specific molecular determinants on protein kinase C stereospecifically recognize structural determinants of phosphatidylserine.