Glycerophospholipids represent the predominant subclass of phospholipids, defined by a glycerol-3-phosphate backbone esterified at the sn-1 and sn-2 positions with fatty acids, and at sn-3 with a polar headgroup via a phosphodiester linkage. This structural organization enables their fundamental role as primary architects of biological membranes. Comprising approximately 70–90% of eukaryotic membrane lipids, glycerophospholipids display stereospecific numbering (sn-configuration) and a wide diversity of acyl chain compositions that finely regulate membrane fluidity, curvature, and function.
Structural Classification
Glycerophospholipids are derived from phosphatidic acid (PA: sn-1/sn-2 diacyl-sn-glycerol-3-phosphate), which is subsequently modified through the attachment of distinct polar headgroups. Major subclasses include phosphatidylcholine (PC, choline), phosphatidylethanolamine (PE, ethanolamine), phosphatidylserine (PS, serine), phosphatidylinositol (PI, inositol), phosphatidylglycerol (PG), and cardiolipin (CL, diphosphatidylglycerol). Typically, the sn-1 position contains saturated fatty acids (16:0 or 18:0), whereas the sn-2 position is enriched in polyunsaturated chains (18:2, 20:4, 22:6). Additional structural variants include plasmalogens (sn-1 vinyl ether linkage) and lysophospholipids, which contain only a single acyl chain.
Biophysical Characteristics
As amphipathic molecules, glycerophospholipids exhibit shapes ranging from conical (e.g., PE, favoring hexagonal HII phases) to cylindrical (e.g., PC, promoting bilayer formation). They spontaneously self-assemble into lipid bilayers approximately 4–5 nm thick, with membrane phase behavior strongly influenced by acyl chain unsaturation and cholesterol content. While PC is zwitterionic with an overall neutral charge, PS and PI are anionic phospholipids contributing to membrane surface charge and signaling functions. These lipids undergo characteristic phase transitions from gel (Lβ′) to ripple (Pβ′) and ultimately to the fluid liquid-crystalline state (Lα).
