Site-specific N-glycosylation of human chorionic gonadotrophin—structural analysis of glycopeptides by one- and two-dimensional1H NMR spectroscopy

摘要: Glycopeptides representing individual N-glycosylation sites of the heterodimeric glycoprotein hormone human chorionic gonadotrophin (hCG) were obtained from subunits hCG alpha (N-glycosylated at Asn-52 and Asn-78) beta Asn-13 Asn-30) by digestion with trypsin chymotrypsin, respectively. Following purification reverse-phase HPLC identification amino acid sequencing, glycopeptides analysed one- two-dimensional 1H NMR spectroscopy. The results are summarized as follows: (i) oligosaccharides attached to comprised monosialylated 'monoantenary' NeuAc 2-3Gal 1-4GlcNAc 1-2Man 1-3[Man 1-6]Man (N1-4'), disialylated diantennary 1-3[NeuAc 2-3-Gal (N2), hybrid-type structures 1-3Man (N1-A) 2-3Gal-beta 1-3(Man 1-6)Man (N1-AB) in a ratio approaching 5:2:2:1; (ii) Asn-78 carried N2 N1-4' almost exclusively (ratio approximately 3:2); (iii) both contained predominantly component N2, partially (approximately 25%) completely 1-6-fucosylated N-acetylglucosamine linked Asn-30, distinct site-specific distribution oligosaccharide among appears reflect primarily influence surrounding protein structure on substrate accessibility Golgi processing enzymes alpha-mannosidase II, GlcNAc transferase II 1,6-fucosyltransferase.