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Fig. 1 | Orphanet Journal of Rare Diseases

Fig. 1

From: The Glycosylphosphatidylinositol biosynthesis pathway in human diseases

Fig. 1

A scheme for the overall GPI-APs biosynthetic pathway, structural remodeling and transport. The whole biosynthetic steps can be divided into three parts: biosynthesis of GPI anchor, attachment of protein and GPI anchor, remodeling of GPI-APs. a) GPI anchor is synthesized in the ER from free PI through 11 steps [transfer of GlcNAc to PI, de-N-acetylation, acylation of the inositol ring, transfer of three mannoses, transfer of three ethanolamine phosphates, currently unknown: GlcN-PI flips from the cytoplasmic side to the luminal side, lipid structure changes from diacyl PI to a mixture of 1-alkyl, 2-acyl PI and diacyl PI in GlcN-(acyl) PI] which involves more than 17 genes, most of them are named PIG genes. The first two steps take place on the cytoplasmic side of the ER, whereas subsequent steps occur on the luminal side. b) The precursor proteins are synthesized independent of the GPI and processed by the GPI-transamidase complex encoded by five genes. c) Post-translational modification after attachment of protein and GPI anchor involving PGAP (post-GPI-attachment to proteins) genes, includes structural remodeling of the glycan and lipid portions of the GPI anchor, removing an acyl chain from the inositol and an EtN-P from Man-2. GPI-APs are then transported to the cell surface through the Golgi, where additional structural remodeling occurs, namely fatty acid

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