Heterogeneity of O-glycosylation in the hinge region of human IgA1

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry was applied to studies of the molecular heterogeneity of desi alylated human IgAl hinge region glycopeptides released with two IgAl prote ases. Typically, the hinge region of an alpha1 chain contains three to five O-linked glycan chains. Variants of the hinge region peptides released fro m IgAl(Kni) myeloma protein carrying 0, 1, 2, or 3 GalNAc residues were obs erved in the mass spectra as well as the nonglycosylated peptide. Variable numbers of Gal residues indicated additional heterogeneity in O-glycosylati on of IgAl. In the hinge region preparation from normal human serum IgAl, g lycopeptides carrying 2, 3, 3, or 5 GalNAc residues with variable numbers o f Gal residues were detected. In conclusion, our new approach using the sit e-specific cleavage with two IgAl proteases allowed precise and sensitive M ALDI-TOF mass spectrometric analysis of O-glycosylation heterogeneity in Ig Al hinge region. (C) 2001 Elsevier Science Ltd. All rights reserved.