Abstract
The attachment of proteins to the cell membrane using a glycosylphosphatidylinositol (GPI) anchor is a ubiquitous process in eukaryotic cells. Deficiencies in the biosynthesis of GPIs and the concomitant production of GPI-anchored proteins lead to a series of rare and complicated disorders associated with inherited GPI deficiencies (IGDs) in humans. Currently, there is no treatment for patients suffering from IGDs. Here, we report the design, synthesis, and use of GPI fragments to rescue the biosynthesis of GPI-anchored proteins (GPI-APs) caused by mutation in genes involved in the assembly of GPI-glycolipids in cells. We demonstrated that the synthetic fragments GlcNAc-PI (1), Man-GlcN-PI (5), and GlcN-PI with two (3) and three lipid chains (4) rescue the deletion of the GPI biosynthesis in cells devoid of the PIGA, PIGL, and PIGW genes in vitro. The compounds allowed for concentration-dependent recovery of GPI biosynthesis and were highly active on the cytoplasmic face of the endoplasmic reticulum membrane. These synthetic molecules are leads for the development of treatments for IGDs and tools to study GPI-AP biosynthesis.
Highlights
Glycosylphosphatidylinositols (GPIs) are complex glycolipids attaching many eukaryotic proteins to the cell membrane.[1]
Glycolipids 1−5 resemble the products and substrates of the enzymes involved in the four initial steps of GPI biosynthesis (Figure 2b)
We designed and synthesized a series of glycolipids corresponding to the initial products of the GPI biosynthesis in eukaryotes
Summary
Glycosylphosphatidylinositols (GPIs) are complex glycolipids attaching many eukaryotic proteins to the cell membrane.[1] GPIs are added as a post-translational modification to the C-terminus of proteins that contain a signal peptide sequence directing GPI attachment.[2] Around 150 human proteins use GPI for anchoring to the cell membrane forming GPI-anchored proteins (GPIAPs).[3] The proteins include hydrolytic enzymes, adhesion molecules, protease inhibitors, receptors, and regulatory proteins of the immune system.[4] The structure of all GPIs has a conserved core structure having the pseudopentasaccharide glycan core Man-α-(1 → 2)-Man-α-(1 → 6)-Man-α-(1 → 4)GlcN-α-(1 → 6)-myo-Ino, a phosphoethanolamine unit (PEtN), and a phospholipid (Figure 1a).[1] This structure can be modified in a cell- and tissue-dependent manner with additional glycans and fatty acid chains and by phosphorylation.[5] Two additional units are common in mammalian GPIs: a PEtN at the 2-O position and a GalNAc branch at the 4-O position on the Man-1 (Figure 1b).[6] Further modifications of mammalian GPI glycans include a Man-4 residue that is attached to the 2-O position of Man-3 and the addition of galactose and N-acetylneuraminic acid to the GalNAc branch,[7] among others
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