A general and convergent synthesis of diverse glycosylphosphatidylinositol glycolipids

Abstract

Glycosylphosphatidylinositol (GPI) glycolipids anchor a large number of proteins in the cell membrane of eukaryotic cells. Their conserved pseudopentasaccharide core carries additional phosphoethanolamine, saccharide and lipid substituents. These structural variations are characteristic for a species or a tissue but their functional significance remains largely unknown. Studies that would link a specific function to a structurally unique GPI rely on availability of homogeneous samples of these glycolipids. To address this need we have developed a general synthetic route to GPI glycolipids. Our convergent synthesis starts from common building blocks and relies on a fully orthogonal set of protecting groups that enables the regioselective introduction of phosphodiesters and efficient assembly of the GPI glycans. Here, we report on the development of this synthetic strategy, evaluation of the set of protecting groups with respect to phosphorylation methods, evaluation of the assembly plan for the GPI glycan, optimization of the glycosylation reactions, and the application of this strategy to the total syntheses of four structurally diverse branched GPI glycolipids.

Recent progress in synthetic and biological studies of GPI anchors and GPI-anchored proteins

“…A key feature of this strategy is that the central mannose block, 5 or 6, had several orthogonal protections that enabled regioselective introduction of any branching observed in nature. Its applicability was demonstrated by the synthesis of a Toxoplasma gondii GPI 7 with a disaccharide at the Man-I 4- O -position (Figure 3B) [38]. …”

Prion protein—Semisynthetic prion protein (PrP) variants with posttranslational modifications

“…Based on that, in CFC assays, Baron and Caughey investigated the impact of GPI‐anchoring of PrP associated with model membranes on PrP res formation. PrP was isolated by immunoprecipitation from mammalian cell lines expressing GPI‐anchored and anchorless PrP, respectively . GPI‐anchored PrP bound to liposomes could not be converted to PrP res upon exposure to exogenous PrP res in microsomes until phosphatidylinositol‐specific phospholipase C (PI‐PLC) was added or the combined membrane fractions were treated with a membrane‐fusing agent.…”

Zwischen Protein und Membran

“…Dadurch sind verschiedene spezifische Modifizierungen erst in den letzten Schritten der Synthese schnell einzuführen. Da es zeitaufwendig ist, die notwendigen Bausteine für die Synthese komplexer Kohlenhydrate jeweils einzeln herzustellen, sparen universelle Bausteine Zeit und Ressourcen und erhöhen gleichzeitig die synthetische Leistung signifikant 12…”