Diacylglycerols (DAGs), also known as diglycerides, are neutral glycerolipids consisting of a glycerol backbone esterified with two fatty acyl chains, typically at the sn-1 and sn-2 positions. These versatile lipids serve as key metabolic intermediates, intracellular second messengers, and structural components involved in membrane organization and cellular signaling pathways.
Chemical Structure
DAG molecules are composed of a central glycerol moiety bearing two hydrophobic fatty acid chains that may vary in length, degree of saturation, and stereochemical position. This structural diversity generates numerous molecular species, such as 1-stearoyl-2-arachidonoyl-sn-glycerol, commonly produced during phospholipase C–mediated hydrolysis of phosphatidylinositol phosphates. Three regioisomeric forms exist (1,2-, 1,3-, and 2,3-DAG), with 1,2-sn-DAG predominating in biological systems due to enzymatic stereospecificity. The sn-2 acyl chain often adopts a bent conformation, initially oriented parallel to the lipid bilayer before aligning with the sn-1 chain.
Physical Properties
In the pure state, DAGs exhibit polymorphic behavior, including β′ crystalline phases (stable monoclinic structures with tilted hydrocarbon chains), lamellar arrangements, and fluid phases. Owing to their small polar headgroup relative to their acyl chains, DAGs favor negative membrane curvature. When incorporated into phospholipid bilayers, they tend to segregate into DAG-enriched microdomains, induce dehydration of neighboring phospholipid headgroups, and localize approximately two methylene units deeper within the membrane core compared with surrounding lipids. These properties facilitate membrane fusion events and the formation of non-lamellar lipid phases.
Biosynthesis and Metabolism
DAGs are generated primarily through two major pathways: dephosphorylation of phosphatidic acid in the Kennedy pathway, and phospholipase C–mediated hydrolysis of membrane phospholipids. These reactions link DAG metabolism to the biosynthesis of triacylglycerols, phosphatidylcholine, and phosphatidylethanolamine. Lipin family phosphatidic acid phosphatases and diacylglycerol acyltransferase (DGAT) enzymes regulate the interconversion between phosphatidic acid, DAG, and triacylglycerols. Regioisomer composition is further refined through acyl chain remodeling catalyzed by lipases and acyltransferases.
