Conformational Dynamics and Activation of Membrane-Associated Human Group IVA Cytosolic Phospholipase A (cPLA).

Cytosolic phospholipase A (cPLA) 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 cPLA associates with the endoplasmic reticulum (ER) membrane of macrophages, where it acts. We found that membrane association causes the lid region of cPLA 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 PIP from the membrane. The active site of the open form of cPLA, containing catalytic dyad residues S228 and D549, exhibited a 3-fold larger cavity than the closed form of cPLA in aqueous solution. These findings provide mechanistic insight into how cPLA-ER membrane association promotes major transitions between conformational states critical to allosteric activation and enzymatic phospholipid hydrolysis.