Conformational dynamics and activation of membrane-associated human Group IVA cytosolic phospholipase A ₂ (cPLA ₂ )

Cytosolic phospholipase A ₂ (cPLA ₂ ) 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 ₂ associates with the endoplasmic reticulum (ER) membrane of macrophages where it acts. We found that membrane association causes the lid region of cPLA ₂ 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 binds the allosteric activator PIP ₂ in the membrane. The active site of the open form of cPLA ₂ , containing the catalytic dyad residues S228 and D549, exhibited a three-fold larger cavity than the closed form of cPLA ₂ in aqueous solution. These findings provide mechanistic insight as to how cPLA ₂ ER membrane association promotes major transitions between conformational states critical to allosteric activation and enzymatic phospholipid hydrolysis.