Recognition of Bisecting N-Glycans on Intact Glycopeptides by Two Characteristic Ions in Tandem Mass Spectra

Bisecting N-glycan represents one of the most important modifications to the N-glycan core, and it is involved in various biological processes. Despite many studies on the biological roles of bisecting N-glycans, current approaches for bisecting N-glycan analysis mainly rely on the use of the lectin PHA-E, which are of low specificity and sensitivity. Here, we describe a straightforward method for the recognition of bisecting N-glycans on intact glycopeptides using two characteristic Y ions [peptide+HexNAc(3)Hex(1)] and [peptide+HexNAc(3)Hex(1)Fuc(1)] in low energy fragmented MS/MS spectra under higher energy collisional dissociation (HCD) mode. The critical aspect of the method is the combination use of low energy HCD fragmentation and intact glycopeptide analysis. With samples from rat renal tissues, we determined the optimal fragmentation energies and analyzed the influence of core fiicosylation on the intensity of the [peptide+HexNAc(3)Hex(1)] ion. Using the method, we identified 183 intact glycopeptides with bisecting N-glycans and investigated the primary bisecting N-glycan structures and the possible biological roles of these identified proteins.