Extracting both peptide sequence and glycan structural information by 157 nm photodissociation of N-linked glycopeptides.

The 157 nm photodissociation of N-linked glycopeptides was investigated in MALDI tandem time-of-flight (TOF) and linear ion trap mass spectrometers. Singly charged glycopeptides yielded abundant peptide and glycan fragments. The peptide fragments included a series of x-, y-, v-, and w- ions with the glycan remaining intact. These provide information about the peptide sequence and the glycosylation site. In addition to glycosidic fragments, abundant cross-ring glycan fragments that are not observed in low-energy CID were detected. These fragments provide insight into the glycan sequence and linkages. Doubly charged glycopeptides generated by nanospray in the linear ion trap mass spectrometer also yielded peptide and glycan fragments. However, the former were dominated by low-energy fragments such as b- and y- type ions while glycan was primarily cleaved at glycosidic bonds.