Primary structure of the glycans from human lactotransferrin.

The polypeptide chain of human lactotransferrin possesses two glycoslyation sites to which glycans are linked through an N-(beta-aspartyl)-N-acetylglucosaminylamine bond and which are structurally heterogenous. After chymotryptic or pronase digestions, glycopeptides with five different glycan structures could be isolated. For three of them, the structure has been determined by the application of methanolysis, methylation analysis, hydrazinolysis/nitrous deamination, enzymatic cleavage and 1H-NMR spectroscopy at 360 MHz: Glycopeptides A and B: NeuAc(alpha 2-6)Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-3)[NeuAc(alpha 2-6)Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-6)]Man(beta 1-4)GlcNAc(beta-1-4)[Fuc(alpha 1-6)]GlcNAc(beta 1-)Asn; Glycopeptide C: NeuAc(alpha 2-6)(Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-3)(Gal(beta 1-4)[Fuc(alpha 1-3)]GlcNAc(beta 1-2)Man(alpha 1-6))Man(beta 1-4)GlcNAc(beta 1-4)[Fuc(alpha 1-6)]GlcNAc(beta 1-)Asn. Glycopeptide D: NeuAc(alpha 2-6)Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-3)[Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-6)]Man(beta 1-4)Glc-NAc(beta 1-4)[Fuc(alpha 1-6)]GlcNAc(beta 1-)Asn. Two other glycopeptides were obtained in very low amount and possess more complex structures.