Differentiation between isomeric triantennary N linked glycans by negative ion tandem mass spectrometry and confirmation of glycans containing galactose attached to the bisecting beta1 4 GlcNAc residue in N glycans from IgG
Negative ion tandem mass spectrometry (MS/MS) spectra of three isomeric triantennary N-linked glycans provided clear differentiation between the isomers and confirmed the occurrence of an isomer that was substituted with galactose on a bisecting GlcNAc (1 --> 4-substituted on the core mannose) residue recently reported by Takegawa et al. from N-glycans released from human immunoglobulin G (IgG). We extend this analysis of human serum IgG to reveal an analogue of the fucosylated triantennary glycan reported by Takegawa et al. together with a third compound that lacked both the sialic acid and the fucose residues. In addition, we demonstrate the biosynthesis of bisected hybrid-type glycans with the galactose modification, with and without core fucose, on the stem cell marker glycoprotein, 19A, expressed in a partially ricin-resistant human embryonic kidney cell line. It would appear, therefore, that this modification of N-linked glycans containing a galactosylated bisecting GlcNAc residue may be more common than originally thought. Negative ion MS/MS analysis of glycans is likely to prove an invaluable tool in the analysis and monitoring of therapeutic glycoproteins.
Rapid Commun. Mass Spectrom.
Harvey DJ, Crispin M, Scanlan C, Singer BB, Lucka L, Chang VT, Radcliffe CM, Thobhani S, Yuen CT, Rudd PM