Abstract
Glycosylphosphatidylinositols (GPIs) act as membrane anchors of many eukaryotic cell surface proteins. GPIs in various organisms have a common backbone consisting of ethanolamine phosphate (EtNP), three mannoses (Mans), one non-N-acetylated glucosamine, and inositol phospholipid, whose structure is EtNP-6Manα-2Manα-6Manα-4GlNα-6myoinositol-P-lipid. The lipid part is either phosphatidylinositol of diacyl or 1-alkyl-2-acyl form, or inositol phosphoceramide. GPIs are attached to proteins via an amide bond between the C-terminal carboxyl group and an amino group of EtNP. Fatty chains of inositol phospholipids are inserted into the outer leaflet of the plasma membrane. More than 150 different human proteins are GPI anchored, whose functions include enzymes, adhesion molecules, receptors, protease inhibitors, transcytotic transporters, and complement regulators. GPI modification imparts proteins with unique characteristics, such as association with membrane microdomains or rafts, transient homodimerization, release from the membrane by cleavage in the GPI moiety, and apical sorting in polarized cells. GPI anchoring is essential for mammalian embryogenesis, development, neurogenesis, fertilization, and immune system. Mutations in genes involved in remodeling of the GPI lipid moiety cause human diseases characterized by neurological abnormalities. Yeast Saccharomyces cerevisiae has >60 GPI-anchored proteins (GPI-APs). GPI is essential for growth of yeast. In this review, we discuss biosynthesis of GPI-APs in mammalian cells and yeast with emphasis on the lipid moiety.
Highlights
Glycosylphosphatidylinositols (GPIs) act as membrane anchors of many eukaryotic cell surface proteins
GPIs act as membrane anchors of many cell surface proteins after they are covalently attached to the C termini of the proteins as a posttranslational modification
GPIs in various organisms have a common backbone consisting of ethanolamine phosphate (EtNP), three mannoses (Mans), one non-Nacetylated glucosamine (GlcN), and inositol phospholipid, whose structure is EtNP-6Man␣-2Man␣-6Man␣-4GlN␣6myoinositol-P-lipid (Fig. 1A) [4,5,6]
Summary
Glycosylphosphatidylinositols (GPIs) act as membrane anchors of many eukaryotic cell surface proteins. The removal of unsaturated fatty acid is mediated by a Golgi resident membrane protein, PGAP3, that is a GPI-specific phospholipase A2 (step 15 in Fig. 4) [25]. 15 Fatty acid remodeling PGAP3 Golgi Unsaturated acyl chain Defective raft association HPMRS4 DD/ID, Sz, HP, hypotonia remained
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