Anionic lipids activate group IVA cytosolic phospholipase A2 via distinct and separate mechanisms (original) (raw)

2007, Journal of Lipid Research

Previously, ceramide-1-phosphate (C1P) and phosphatidylinositol-4,5-bisphosphate [PI(4,5)P 2 ] were demonstrated to be potent and specific activators of group IVA cytosolic phospholipase A 2 (cPLA 2 a). In this study, we hypothesized that these anionic lipids functionally activated the enzyme by distinctly different mechanisms. Indeed, surface plasmon resonance and surface dilution kinetics demonstrated that C1P was a more potent effector than PI(4,5)P 2 in decreasing the dissociation constant of the cPLA 2 a-phosphatidylcholine (PC) interaction and increasing the residence time of the enzyme on the vesicles/micelles. PI(4,5)P 2 , in contrast to C1P, decreased the Michaelis-Menten constant, increasing the catalytic efficiency of the enzyme. Furthermore, PI(4,5)P 2 activated cPLA 2 a with a stoichiometry of 1:1 versus C1P at 2.4:1. Lastly, PI(4,5)P 2 , but not C1P, increased the penetration ability of cPLA 2 a into PC-rich membranes. Therefore, this study demonstrates two distinct mechanisms for the activation of cPLA 2 a by anionic lipids. First, C1P activates cPLA 2 a by increasing the residence time of the enzyme on membranes. Second, PI(4,5)P 2 activates the enzyme by increasing catalytic efficiency through increased membrane penetration.