α2,3 linkage of sialic acid to a GPI anchor and an unpredicted GPI attachment site in human prion protein

• Published in: The Journal of biological chemistry Vol. 295; no. 22; pp. 7789 - 7798
• Main Authors: Kobayashi, Atsushi, Hirata, Tetsuya, Nishikaze, Takashi, Ninomiya, Akinori, Maki, Yuta, Takada, Yoko, Kitamoto, Tetsuyuki, Kinoshita, Taroh
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 29.05.2020; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Carbohydrate Conformation; Creutzfeldt–Jakob disease; Glycobiology and Extracellular Matrices; glycosylation; glycosylphosphatidylinositol (GPI); Glycosylphosphatidylinositols - chemistry; Glycosylphosphatidylinositols - genetics; Glycosylphosphatidylinositols - metabolism; Humans; Male; Mesocricetus; Mice; Mice, Knockout; N-Acetylneuraminic Acid - chemistry; N-Acetylneuraminic Acid - genetics; N-Acetylneuraminic Acid - metabolism; neurodegeneration; prion; Prion Diseases - genetics; Prion Diseases - metabolism; Prion Diseases - pathology; Prion Proteins - chemistry; Prion Proteins - genetics; Prion Proteins - metabolism; PrPC Proteins - chemistry; PrPC Proteins - genetics; PrPC Proteins - metabolism; scrapie; sialic acid; sialic acid; MS; neurodegeneration; glycosylphosphatidylinositol (GPI); glycosylation; prion; scrapie; Creutzfeldt–Jakob disease
• DOI: 10.1074/jbc.RA120.013444
• ISSN: 0021-9258

Prion diseases are transmissible, lethal neurodegenerative disorders caused by accumulation of the aggregated scrapie form of the prion protein (PrPSc) after conversion of the cellular prion protein (PrPC). The glycosylphosphatidylinositol (GPI) anchor of PrPC is involved in prion disease pathogenesis, and especially sialic acid in a GPI side chain reportedly affects PrPC conversion. Thus, it is important to define the location and structure of the GPI anchor in human PrPC. Moreover, the sialic acid linkage type in the GPI side chain has not been determined for any GPI-anchored protein. Here we report GPI glycan structures of human PrPC isolated from human brains and from brains of a knock-in mouse model in which the mouse prion protein (Prnp) gene was replaced with the human PRNP gene. LC–electrospray ionization–MS analysis of human PrPC from both biological sources indicated that Gly229 is the ω site in PrPC to which GPI is attached. Gly229 in human PrPC does not correspond to Ser231, the previously reported ω site of Syrian hamster PrPC. We found that ∼41% and 28% of GPI anchors in human PrPCs from human and knock-in mouse brains, respectively, have N-acetylneuraminic acid in the side chain. Using a sialic acid linkage-specific alkylamidation method to discriminate α2,3 linkage from α2,6 linkage, we found that N-acetylneuraminic acid in PrPC's GPI side chain is linked to galactose through an α2,3 linkage. In summary, we report the GPI glycan structure of human PrPC, including the ω-site amino acid for GPI attachment and the sialic acid linkage type.