Group IVB, IVD, IVE, and IVF cytosolic phospholipase A2; catalytic domain; Ca-dependent
Group IVB, IVD, IVE, and IVF cPLA2 consists of two domains: the regulatory C2 domain and alpha/beta hydrolase PLA2 domain. Group IVB, IVD, IVE, and IVF cPLA2 are also referred to as cPLA2-beta, -delta, -epsilon, and -zeta respectively. cPLA2-beta is approximately 30% identical to cPLA2-alpha and it shows low enzymatic activity compared to cPLA2alpha. cPLA2-beta hydrolyzes palmitic acid from 1-[14C]palmitoyl-2-arachidonoyl-PC and arachidonic acid from 1-palmitoyl-2[14C]arachidonoyl-PC, but not from 1-O-alkyl-2[3H]arachidonoyl-PC. cPLA2-delta, -epsilon, and -zeta are approximately 45-50% identical to cPLA2-beta and 31-37% identical to cPLA2-alpha. It's possible that cPLA2-beta, -delta, -epsilon, and -zeta may have arisen by gene duplication from an ancestral gene. The catalytic domain of cytosolic phospholipase A2 (PLA2; EC 220.127.116.11) hydrolyzes the sn-2-acyl ester bond of phospholipids to release arachidonic acid. At the active site, cPLA2 contains a serine nucleophile through which the catalytic mechanism is initiated. The active site is partially covered by a solvent-accessible flexible lid. cPLA2 displays interfacial activation as it exists in both "closed lid" and "open lid" forms. Movement of the cPLA2 lid possibly exposes a greater hydrophobic surface and the active site. cPLA2 belongs to the alpha-beta hydrolase family which is identified by a characteristic nucleophile elbow with a consensus sequence of Sm-X-Nu-Sm (Sm = small residue, X = any residue and Nu = nucleophile). Calcium is required for cPLA2 to bind with membranes or phospholipids. The calcium-dependent phospholipid binding domain resides in the N-terminal region of cPLA2; it is homologous to the C2 domain superfamily which is not included in this hierarchy. It includes PLA2G4B, PLA2G4D, PLA2G4E, and PLA2G4F from humans.