A novel dimeric active site and regulation mechanism revealed by the crystal structure of iPLA₂β

Abstract

Calcium-independent phospholipase A 2 β (iPLA 2 β) regulates several physiological processes including inflammation, calcium homeostasis and apoptosis. It is linked genetically to neurodegenerative disorders including Parkinson's disease. Despite its known enzymatic activity, the mechanisms underlying pathologic phenotypes remain unknown. Here, we present the first crystal structure of iPLA 2 β that significantly revises existing mechanistic models. The catalytic domains form a tight dimer. The ankyrin repeat domains wrap around the catalytic domains in an outwardly flared orientation, poised to interact with membrane proteins. The closely integrated active sites are positioned for cooperative activation and internal transacylation. A single calmodulin binds and allosterically inhibits both catalytic domains.These unique structural features identify the molecular interactions that can regulate iPLA 2 β activity and its cellular localization, which can be targeted to identify novel inhibitors for therapeutic purposes. The structure provides a well-defined framework to investigate the role of neurodegenerative mutations and the function of iPLA 2 β in the brain.Introduction.

Membrane Association Allosterically Regulates Phospholipase A2 Enzymes and Their Specificity

“…1 It is worth mentioning that homology modeling and later the crystal structure revealed an ankyrin repeat region along with the catalytic domain of iPLA 2 that did not show any interactions with the membrane bilayer. 1,18 Similar HDX-MS studies were performed on cPLA 2 to identify the peptide regions of the interfacial surface that interact with the membrane. The cPLA 2 structure contains a C2 domain along with the catalytic domain that was thought to assist the association of the enzyme with the membrane through its calcium binding site.…”