Identification of a tetrasialylated monofucosylated tetraantennary N-linked carbohydrate chain in human platelet glycocalicin

AbstractGlycocalicin (140 kDa), the main constituent of the glycoprotein Ib α-chain (150 kDa) of the human platelet membrane, contains 4 putative N-glycosylation sites. For the structural analysis of the N-glycosidic carbohydrate chains of glycocalicin, the glycoprotein has been subjected to the hydrazinolysis procedure. The acidic carbohydrate chains obtained were fractionated by ion-exchange chromatography on DEAE-Sephadex A-25, subsequently analysed by sugar analysis, anion-exchange chromatography on Mono Q HR 5/5 500 MHz 1H-NMR spectroscopy. A novel tetrasialylated monofucosylated tetraantennary chain was identified in the glycoprotein. It could also be deduced that in all structures the α2→6-linked NeuAc is attached exclusively at the Galβ1→4GlcNAcβ1→2Manα1→3 antenna, whereas the other antennae can be terminated with α2→3-linked NeuAc. As minor constituents sialylated N-linked carbohydrate chains with a terminal Fucα1→2Galβ1→. sequence were detected