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

Abstract

The asialoglycopeptides obtained from secretory IgA from human milk were separated by gel filtration and affinity chromatography on Concanavalin A-Sepharose and Lens culinaris agglutinin-Sepharose columns. Their structures were 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 presented. Most of the asialoglycopeptide structures possess an intersecting GlcNAc residue; they are suggested to be located on the .alpha. chain of the secretory IgA of human milk. The nonintersected structures probably occur on the secretory piece. The methodology applied to the structural analysis adequately coped with the extremely high degree of heterogeneity shown by the structures.