Structures of the O-glycosidically linked oligosaccharides of human IgD

In the previous communication, the structures of the oligosaccharides present at the 3 asparagine glycosylation sites of a human IgD myeloma protein were defined. In this communication, we present the structures of the O-glycosidically linked oligosaccharides located in the hinge region of IgD:WAH. Three or four threonine residues and one serine residue in the region bear O-glycosidically linked oligosaccharides. Approximately 50% of these molecules have the structure Galβ1→3GalNAc which is identical with the structure of the predominant oligosaccharide in the hinge region of human IgA, myeloma proteins. The remainder of the oligosaccharides contain 1 or 2 residues of N-acetylneuraminic acid and have the structures NeuAcα2→3Galβ1→3GalNAc (30%), Galβ1→(NeuAcα2→6)GalNAc (12%), and NeuAcα2→3Galβ1→3(NeuAcα2→6)GalNAc (8%). The sialylated molecules have not been encountered previously on other human immunoglobulin heavy chains. These structures, however, have been described on a number of secreted and membrane glycoproteins. Examination of oligosaccharides isolated from different subregions of the IgD hinge indicated that a specific distribution of the sialylated structures among the glycosylated amino acids of the hinge region is not likely.