Evidence for a site-specific fucosylation of N-linked oligosaccharide of immunoglobulin A1 from normal human serum

Glycopeptides containing the N-linked oligosaccharide from human serum IgA1 were analyzed by matrix-assisted laser desorption ionization time-of-fligh t mass spectrometry (MALDI-TOFMS). Two glycopeptides, GP1 and GP2, prepared from the endoproteinase Asp-N digest of the IgA1 heavy chain, were derived from the CH2 domain (N-glycan site at Asn(263)) and the tailpiece portion (N-glycan site at Asn(459)), respectively. The structure of the attached su gar chain was deduced from the mass number of the glycopeptide and confirme d by a two-dimensional mapping technique for a pyridylaminated oligosacchar ide. GP1 was composed of two major components having a fully galactosylated bianntena sugar chain with or without a bisecting N-acetylglucosamine (Glc NAc) residue. On the other hand, the GP2 fraction corresponded to the glyco peptides having a fully galactosylated and fucosylated bianntena sugar chai n partly bearing a bisecting GlcNAc residue. Thus, the site-specific fucosy lation of the N-linked oligosaccharide on the tailpiece of the al chain bec ame evident for normal human serum IgA1.