Characterization of protein glycoforms by capillary-zone electrophoresis nanoelectrospray mass spectrometry

The investigation of N- and O-linked glycoproteins using capillary-zone electrophoresis interfaced with nanoelectrospray mass spectrometry is described. The combination of high-resolution separation with high-sensitivity mass spectrometric detection provides analysis of glycoprotein digests at sample loadings of high femtomoles to low picomoles. Stepped-orifice voltage scanning is used to identify glycopeptides in complex proteolytic digests. Further structural information is obtained using capillary zone electrophoresis (CZE)-MS-MS to elucidate the composition of both N- and O-linked glycopeptide oligosaccharides. Collisional activation in the orifice/skimmer region is used to generate first-generation fragment ions which undergo subsequent dissociation in the r.f.-only collision cell of the triple quadrupole mass spectrometer. These experiments provided informative peptide backbone fragment ions usually not available from fragment ion spectra of multiply protonated glycopeptide ions. These methods were applied to the characterization of alpha-amylase inhibitor 1, a lectin from Lotus tetragonolobus, two N-linked glycoproteins, and to kappa-casein, a glycoprotein comprising O-linked sialylated glycans. Crown Copyright (C) 1998 Published by Elsevier Science B.V.