Toward understanding interfacial activation of secretory phospholipase A2 (PLA2):: Membrane surface properties and membrane-induced structural changes in the enzyme contribute synergistically to PLA2 activation

Phospholipase A(2) (PLA(2)) hydrolyzes phospholipids to free fatty acids and lysolipids and thus initiates the biosynthesis of eicosanoids and platelet-activating factor, potent mediators of inflammation, allergy, apoptosis, and tumorigenesis. The relative contributions of the physical properties of membranes and the structural changes in PLA(2) to the interfacial activation of PLA(2), that is, a strong increase in the lipolytic activity upon binding to the surface of phospholipid membranes or micelles, are not well understood. The present results demonstrate that both binding of PLA(2), to phospholipid bilayers and its activity are facilitated by membrane surface electrostatics. Higher PLA(2) activity toward negatively charged membranes is shown to result from stronger membrane-enzyme electrostatic interactions rather than selective hydrolysis of the acidic lipid. Phospholipid hydrolysis by PLA(2) is followed by preferential removal of the liberated lysolipid and accumulation of the fatty acid in the membrane that may predominantly modulate PLA(2) activity by affecting membrane electrostatics and/or morphology. The previously described induction of a flexible helical structure in PLA(2) during interfacial activation was more pronounced at higher negative charge densities of membranes. These findings identify a reciprocal relationship between the membrane surface properties, strength of membrane binding of PLA(2), membrane-induced structural changes in PLA(2), and the enzyme activation.