Structures of the Asparagine-Linked Sugar Chains of Human Chorionic Gonadotropin1

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Abstract
The asparagine-linked sugar chains of human chorionic gonadotropin were released from the polypeptide moiety by hydrazinolysis followed by N-acetylation and NaB3H4 reduction. More than 90% of the released radioactive oligosaccharides contained N-acetylneuraminic acid residues. After removal of N-acetylneuraminic acid residues by sialidase treatment, two neutral oligosaccharide fractions were obtained by paper chromatography. Sequential exoglycosidase digestion revealed that one of them was a mixture of two neutral oligosaccharides. The complete structures of the three oligosaccharides were elucidated by methylation analysis. It was confirmed that all the N-acetylneuraminic acid residues of the asparagine-linked sugar chains of human chorionic gonadotropin occur as NeuAcα2→3Gal groupings by comparing the methylation analysis data for the acidic oligosaccharide mixture before and after sialidase treatment. Based on these results, the structures of the asparagine-linked sugar chains of human chorionic gonadotropin were confirmed to be ±NeuAcα2→3Galβ1→4GlcNAcβ1→2Manα1→6(NeuAcα2→3Galβ1→4GlcNAcβ1→2Manα1→3)Manβ1→4GlcNacβ1→4(±Fucα1→6)GlcNAc and Manα1→6(NeuAcα2→3Galβ1→4GlcNAcβ1→2Manα1→3)Manβ1→4GlcNAcβ1→4GlcNAc.

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