Glycosylphosphatidylinositol Anchors

Abstract

Glycosylphosphatidylinositol (GPI)-anchored proteins are a class of lipid-anchored membrane proteins that are ubiquitously expressed at the surface of eukaryotic cells. GPI proteins represent roughly 1% of all proteins encoded by eukaryotic genomes. They differ from traditional membrane proteins in that they rely on a complex glycolipid, GPI, rather than a hydrophobic transmembrane sequence for their association with membranes. GPI anchors are found on a variety of functionally diverse proteins (as well as glycoconjugates) including cell-surface receptors (folate receptor, CD14), cell adhesion molecules (neural cell adhesion molecule isoforms and carcinoembryonic antigen variants), cell surface hydrolases (5'-nucleotidase, acetylcholinesterase), complement regulatory proteins (decay accelerating factor), and protozoal surface molecules (Trypanosoma brucei variant surface glycoprotein, Leishmania lipophosphoglycan). Along with serving to attach proteins to the cell surface, GPI-anchored proteins appear to be markers and major constituents of detergent-resistant lipid rafts, the sphingolipid- and sterol-rich domains in membranes that are postulated to play an important role in the activation of signaling cascades.