Structural characterization of murine ia antigen n-linked oligosaccharides and localization of specific structures to two unique α-chain glycosylation sites

Abstract

The sequence of N-linked oligosaccharides of differentially glycosylated murine I-A k α- (α 2- and α 3-) and β-chains was determined. I-A k β-chains predominantly bear a biantennary complex oligosaccharide with a core fucose, and with the peripheral sequence SA→Gal→GlcNAc→Man. The I-A k α-chain has two N-linked glycosylation sites at Asn-82 and Asn-122. When Lubrol-insoluble α 3-chains are examined they are found to bear high-mannose oligosaccharides of either the Man 9GlcNAc 2 or Man 8GlcNAc 2 type at both sites. When Lubrol-soluble α 2-chains are examined, in about 85% of the molecules the Asn-82 site bears a biantennary complex oligosaccharide with core fucose, and with the peripheral sequence SA→Gal→GlcNAc→Man. Interestingly, the Asn-122 site bears a variety of structures. In about 50% of the molecules, the structure at Asn-122 is a biantennary complex oligosaccharide without core fucose and with the peripheral sequence SA→Gal→GlcNAc→Man. In addition, it can bear other complex structures which we did not define further. The apparently restricted addition of fucose to the oligosaccharide at the α-Asn-82 site, even when both α-sites bear biantennary complex structures with the same peripheral sequence, is a feature unique to this system. The unusual variety of structures present at the α-Asn-122 site may indicate differential processing in different cell types.