Conformational Dynamics and Activation of Membrane-Associated Human Group IVA Cytosolic Phospholipase A₂ (cPLA₂)

Cytosolic phospholipase A₂ (cPLA₂) associates with membranes, where it hydrolyzes phospholipids containing arachidonic acid to initiate an inflammatory cascade. All-atom molecular dynamics simulations were employed to understand the activation process when cPLA₂ associates with the endoplasmic reticulum (ER) membrane of macrophages, where it acts. We found that membrane association causes the lid region of cPLA₂ to undergo a closed-to-open state transition that is accompanied by the sideways movement of loop 495-540, allowing the exposure of a cluster of lysine residues (K488, K541, K543, and K544), which are known to bind allosteric activator PIP₂ from the membrane. The active site of the open form of cPLA₂, containing catalytic dyad residues S228 and D549, exhibited a 3-fold larger cavity than the closed form of cPLA₂ in aqueous solution. These findings provide mechanistic insight into how cPLA₂-ER membrane association promotes major transitions between conformational states critical to allosteric activation and enzymatic phospholipid hydrolysis.