Application of matrix-assisted laser desorption ionization time-of-flight mass spectrometry to the analysis of glycopeptide-containing multiple O-linked oligosaccharides

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In our previous report [Iwase et al., J. Biochem., 120 (1996) 393], the number of O-linked oligosaccharide chains on the hinge region of IgA1 was estimated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI–TOFMS). In this experiment, the number of non-substituted N-acetylgalactosamines and Galβ1,3GalNAc residues, as the core O-linked oligosaccharide structure per heavy chain of normal human serum IgA1, was estimated by digestion of the asialo-hinge glycopeptide with α- N-acetylgalactosaminidase (GalNAc-ase) or endo-α- N-acetylgalactosaminidase (endo-GalNAc-ase). GalNAc-ase treatment of the asialoglycopeptide produced two major peaks, one being a glycopeptide containing four GalNAc and four Gal residues, and the other contained three GalNAc and three Gal residues. Treatment with endo-GalNAc-ase also produced a nearly equal amount of the two peaks, with the naked hinge peptide and the peptide having one GalNAc residue. From those results, we concluded that the asialo-hinge glycopeptide was composed of three components bearing four Galβ1,3GalNAc and one GalNAc, only four Galβ1,3GalNAc, and three Galβ1,3GalNAc and one GalNAc, respectively. This method was useful for determining the glycoforms on the IgA1 molecule with respect to the core O-linked oligosaccharide structure.