Each phospholipase A type exhibits distinct selectivity toward sn-1 ester, alkyl ether, and vinyl ether phospholipids.

Glycerophospholipids are major components of cell membranes and have enormous variation in the composition of fatty acyl chains esterified on the sn-1 and sn-2 position as well as the polar head groups on the sn-3 position of the glycerol backbone. Phospholipase A (PLA) enzymes constitute a superfamily of enzymes which play a critical role in metabolism and signal transduction by hydrolyzing the sn-2 acyl chains of glycerophospholipids. In human cell membranes, in addition to the conventional diester phospholipids, a significant amount is the sn-1 ether-linked phospholipids which play a critical role in numerous biological activities. However, precisely how PLAs distinguish the sn-1 acyl chain linkage is not understood. In the present study, we expanded the technique of lipidomics to determine the unique in vitro specificity of three major human PLAs, including Group IVA cytosolic cPLA, Group VIA calcium-independent iPLA, and Group V secreted sPLA toward the linkage at the sn-1 position. Interestingly, cPLA prefers sn-1 vinyl ether phospholipids known as plasmalogens over conventional ester phospholipids and the sn-1 alkyl ether phospholipids. iPLA showed similar activity toward vinyl ether and ester phospholipids at the sn-1 position. Surprisingly, sPLA preferred ester phospholipids over alkyl and vinyl ether phospholipids. By taking advantage of molecular dynamics simulations, we found that Trp30 in the sPLA active site dominates its specificity for diester phospholipids.