Isolation and structural characterization of the smaller-size oligosaccharides from desialylated human κ-casein. Establishment of a novel type of core for a mucin-type carbohydrate chain

Abstract

Alkaline borohydride reductive cleavage (beta-elimination) of desialylated human kappa-caseinoglycopeptide resulted in the release of a series of oligosaccharides. The smaller-size compounds among them were purified to virtual homogeneity by gel filtration followed by high-performance liquid chromatography. The structures of 9 oligosaccharides were determined by 1H-NMR spectroscopy in conjunction with sugar analysis. The tetrasaccharide Gal beta(1->3)[Gal beta(1->4)GlcNAc beta(1->6)]GalNAc-ol and various partial structures thereof were characterized. Notably, the disaccharide GlcNAc beta(1->6)GalNAc-ol and the trisaccharide Gal beta(1->4)GlcNAc beta(1->6)GalNAc-ol were identified; they represent a novel type of core structure for mucin-type carbohydrate chains, namely a peptide-linked GalNAc that is mono-substituted at C-6. In addition, some oligosaccharides ending in GlcNAc-ol could be characterized. Their possible origin is discussed.