Primary structure of N-glycosidically linked asialoglycans of secretory immunoglobulins A from human milk.

The asialoglycopeptides obtained from secretory immunoglobulins A from human milk have been separated by gel filtration and affinity chromatography on Concanavalin A-Sepharose and Lens culinaris agglutinin-Sepharose columns. Their structures have been determined by sugar analysis, methylation studies including mass spectrometry and 500-MHz 1H-NMR spectroscopy. The glycans are of the biantennary N-acetyllactosamine type differing in their degree of extension by fucosyl-N-acetyllactosamine residues. The overall structures of the glycopeptides are as follows: Most of the asialoglycospeptide structures possess an intersecting GlcNAc residue; they are suggested to be located on the α chain of the secretory immunoglobulins A of human milk. The non-interesected structures probably occur on the secretory piece. The methodology applied to the structural analysis adequately coped with the exteremely high degree of heterogeneity shown by the structures.