Phospholipase A2: A Paradigm of Allosteric Regulation by Membranes

Defining the molecular details and consequences of the association of water-soluble proteins with membranes is fundamental to understanding protein–lipid interactions and membrane functioning. Phospholipase A₂ (PLA₂) enzymes, which catalyze the hydrolysis of phospholipid substrates that comprise the membrane bilayer, provide the ideal system for studying protein–lipid interactions. Our research focuses on understanding the catalytic cycle of various recombinant human intracellular PLA₂ enzymes including the GIVA cPLA₂ and GVIA iPLA₂. cPLA₂ is the main arachidonic acid provider for the eicosanoid pathway, while iPLA₂ is involved in membrane phospholipid remodeling.

Hydrogen/deuterium exchange mass spectrometry was used to experimentally identify distinct PLA₂ peptide regions that interact with phospholipid vesicles. Molecular dynamics simulations, guided by the experimental data, showed that the active sites of these enzymes are allosterically regulated by membranes. Membrane phospholipids bind to allosteric sites located on the interfacial surface of PLA₂s shifting their conformation from the “closed” to the “open” state. This process facilitates extraction and binding of a phospholipid molecule in the active site where the hydrolysis occurs. This constitutes the first detailed study describing the binding and interaction mechanism of PLA₂s with the membrane bilayer as well as how they bind a single phospholipid molecule in the catalytic site. These enzymes are implicated in chronic inflammatory diseases and understanding their association with membranes, mechanism of action and interactions at the molecular level, will allow us to identify potent and selective inhibitors that can be further developed as anti-inflammatory agents.