Structure determination of the major N‐ and O‐linked carbohydrate chains of the β subunit from equine chorionic gondotropin

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Abstract
The carbohydrate moieties of equine chorionic gonadotropin .alpha. and .beta. subunits were released from the protein backbones by successive treatments with peptide-N4-(N-acetyl-.beta.-glucosaminyl)asparagine amidase F and alkaline borohydride and then fractionated by FPLC and HPLC. The major N- and O-linked glycans of the .beta. subunits were characterized by 500-MHz 1H-NMR spectroscopy, showing a remarkable structural heterogeneity for the N-glycosidically linked chains, comprising mono-, di-, tri- and tri''-antennary N-acetyllactosamine type of glycans, being partly .alpha.1-6 fucosylated at the Asn-bound GlcNAc residue and having .alpha.2-6 and .alpha.2-3 linked N-acetyl- and N-acetyl-4-O-acetylneuraminic acid residues as sialic acid constituents. Significant differences in this respect were detected for the partially characterized glycans of the .alpha. subunit. The major part of the O-linked carbohydrate chains, occurring solely in the .beta. subunit, is formed by tri-, tetra-, penta- and hexa-saccharides. There are indications for the presence of oligo(N-acetyllactosamine) units in both the N- and O-linked glycans of the .beta. subunit.

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