Infrared multiphoton dissociation and electron capture dissociation of high-mannose type glycopeptides.

The combination of electron capture dissociation (ECD) and infrared multiphoton dissociation (IRMPD) for the structural characterization of high-mannose type glycopeptides is explored in depth for the first time. Contrary to previous applications to other glycan types, our analyses reveal that IRMPD does not necessarily selectively induce glycan cleavage in high-mannose type glycopeptides; rather peptide backbone cleavage can effectively compete with glycosidic cleavage. Poor glycan cleavage with IRMPD is due to a higher gas-phase stability of mannose-linking glycosidic bonds. This reasoning also explains mannose cleavage patterns observed for a xylose type glycopeptide with IRMPD. In addition, extensive peptide backbone cleavage is observed for a >6 kDa glycopeptide with ECD, to our knowledge the largest glycopeptide examined with this technique to date.