Glycosylphosphatidylinositol (GPI anchor) is a glycolipid that can be attached to the C-terminus of a protein during posttranslational modification. Proteins containing a GPI anchor play key roles in a wide variety of biological processes. It is composed of a phosphatidylinositol group linked through a carbohydrate-containing linker (glucosamine and mannose glycosidically bound to the inositol residue) and via an ethanolamine phosphate (EtNP) bridge to the C-terminal amino acid of a mature protein. The two fatty acids within the hydrophobic phosphatidyl-inositol group anchor the protein to the cell membrane.