Interfacial Kinetic and Binding Properties of Mammalian Group IVB Phospholipase A2 (cPLA2β) and Comparison with the Other cPLA2 Isoforms

The cytosolic (group IV) phospholipase A(2) (cPLA(2)s) family contains six members. We have prepared recombinant proteins for human alpha, mouse beta, human gamma, human delta, human epsilon, and mouse zeta cPLA(2)s and have studied their interfacial kinetic and binding properties in vitro. Mouse cPLA(2)beta action on phosphatidylcholine vesicles is activated by anionic phosphoinositides and cardiolipin but displays a requirement for Ca2+ only in the presence of cardiolipin. This activation pattern is explained by the effects of anionic phospholipids and Ca2+ on the interfacial binding of mouse cPLA(2)beta and its C2 domain to vesicles. Ca2+ dependent binding of mouse cPLA(2)beta to cardiolipin-containing vesicles requires a patch of basic residues near the Ca2+-binding surface loops of the C2 domain, but binding to phosphoinositide-containing vesicles does not depend on any specific cluster of basic residues. Human cPLA(2)delta also displays Ca2+- and cardiolipin-enhanced interfacial binding and activity. The lysophospholipase, phospholipase A(1), and phospholipase A(2) activities of the full set of mammalian cPLA(2)s were quantified. The relative level of these activities is very different among the isoforms, and human cPLA(2)delta stands out as having relatively high phospholipase A(1) activity. We also tested the susceptibility of all cPLA(2) family members to a panel of previously reported inhibitors of human cPLA(2)alpha and analogs of these compounds. This led to the discovery of a potent and selective inhibitor of mouse cPLA(2)beta. These in vitro studies help determine the regulation and function of the cPLA(2) family members.