Structural analysis of an N-glycan with β1-4 bisecting branch from human serum IgG by negative-ion MSn spectral matching and exoglycosidase digestion

A novel N-linked oligosaccharide (N-glycan) with beta 1-4 bisecting branch (galactose beta 1-4 bisecting N-acetylglucosamine) was found in human serum IgG. Its structure was efficiently analyzed by using beta-galactosidase digestion, a MSn spectral library database, and negative-ion MS2 spectral matching. For confirmation, the novel N-glycan was synthesized by using an expected standard N-glycan (acceptor), UDP-galactose (donor), and beta 1 -4 galactosyltransferase. This work also demonstrates that the MSn spectral library database, in particular, negative-ion MS2 spectral matching, can efficiently reduce the number of specific, sequential exoglycosidase digestions required and is useful for rapid structural analysis of unknown glycans not in the database.