Panels I and II represent structures of GPI anchors found in lower eukaryotes while panels III and IV represent those observed in higher eukaryotes. With the exception of Entamoeba histolytica proteophosphoglycan (PPG) (panel I), all known protein-linked GPI anchors have the same minimal core structure embellished with species- and tissue-specific side-chain and lipid variations. In mammalian cells, ethanolamine-PO₄ on α1-6-linked Man (Man-2) rather than α1-2-linked Man (Man-3) is preferentially used to attach GPI to some GPI-anchored proteins. Aspergillus fumigatus galactomannan (panel II) is unusual in that it lacks the linking ethanolamine residue; instead its GPI portion is linked to the galactomannan chain via a fourth mannose residue. Those fungal GPI-APs that are present on the cell wall are normally linked to the underlying beta-glucan layer after loss of the glucosaminylphospholipid moiety. Soluble GPI structures are released from the cell surface by the action of phosphatidylinositol-specific phospholipase C (PI-PLC) or GPI-specific phospholipase D (GPI-PLD). (±) Glycosyl heterogeneity; curved arrows for the Saccharomyces examples in panel II, the two terminal αMan residues are mutually exclusive; (*) unknown lipid type or chain length. Chain lengths and degrees of unsaturation of the lipids are indicated. For the monosaccharide symbol code, see Online Appendix 1B. PSP, promastigote surface protease; VSG, variant surface glycoprotein; GARP, glutamic acid/alanine-rich protein; TS, trans-sialidase; VSA, variant surface antigen; GPI-APs, glycosylphosphatidylinositol-anchored proteins; PSA, prespore antigen; AGP, arabinogalactan protein; AChE, acetylcholinesterase; eAChE, erythrocyte acetylcholinesterase; MDP, metallodipeptidase; NCAM, neural cell adhesion molecule; PLAP, placental alkaline phosphatase.