Bacterial expression and characterization of human secretory class V phospholipase A2.

Mammalian secretory class V phospholipase A2 (PLA2) is a newly discovered PLA2 that is implicated in eicosanoid formation in inflammatory cells. As a first step towards understanding the structure, function and regulation of this PLA2, we constructed a bacterial expression vector for human secretory class V PLA2 (hV-PLA2), over-expressed and purified the protein, and determined its physical and kinetic properties. When compared with human class IIa enzyme (hIIa-PLA2), hV-PLA2 has several distinct properties. First, hV-PLA2 can catalyse the hydrolysis of phosphatidylcholine more effectively than hIIa-PLA2 by two orders of magnitude. Secondly, hV-PLA2 has much higher binding affinity and activity for compactly packed phosphatidylcholine bilayers than hIIa-PLA2. Finally, hV-PLA2 has much reduced thermal stability compared with hIIa-PLA2. These data suggest that hV-PLA2 is better suited than hIIa-PLA2 for acting on the outer cellular membrane and liberating arachidonic acid from membrane phospholipids. Also, the unusually low thermal stability of hV-PLA2 might contribute to tighter regulation of its activities in extracellular media.