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

Abstract

Glycocalicin (140 kDa), the main constituent of the glycoprotein Ib alpha-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 alpha2¨6-linked NeuAc is attached exclusively at the Gal beta 1¨4GlcNAc beta 1¨2Man alpha 1¨3 antenna, whereas the other antennae can be terminated with alpha2¨3-linked NeuAc. As minor constituents sialylated N-linked carbohydrate chains with a terminal Fuc alpha1¨2Gal beta1¨. sequence were detected