Fig 4

Illustration of a portion of the catalytic mechanism of HRASLS enzymes including depiction of the thioester intermediate formed during phospholipid hydrolysis. Reaction demonstrating the formation of a thioester intermediate following nucleophilic attack by the anionic sulphur of the deprotonated active site cysteine side chain in HRASLS proteins on the carbonyl group of the sn-1 fatty acyl chain of phosphatidylcholine. Hydrolysis results in the generation of a free lysophospholipid and an enzyme-fatty acyl intermediate that releases the enzyme and a free fatty acid following addition of a hydroxyl group to the carbonyl of the fatty acyl chain, forming a carboxylic acid. All HRASLS enzymes can catalyze complete phospholipase reactions in vitro, resulting in liberation of a free fatty acid as well as a lysophospholipid. All HRASLS enyzmes also show in vitro N- and O-acyltransferase activities, where the enzyme-fatty acyl intermediate binds a glycerolphospholipid leading to production of N-acylphosphatidylethanolamines (NAPEs) or phospholipids, respectively