Compared to transferrin ,which has only two glycosylation sites and limited glycan heterogeneity,AGP is more complex with five different glycosylation sites and differencesin peptide backbone arising from genetic variants
The HILIC-C18 methodwas significantly more effective at acquiring data-dependent tandemmass spectra of sufficient quality to enable identification of thepeptide backbone
We observed formation of useful peptide backboneions, even for precursor ions with moderate abundances (∼1–2× 105 counts)
Tandem mass spectra were useful indiscriminating single amino acid genetic variants ; for example, inTable 2, two AGP glycopeptides have similarpeptide sequences , ENGTVSR and ENGTISR, for which we observed completepeptide sequences in the glycopeptide tandem mass spectra of precursors1070.6586 (4+) and 1074.1627 (4+)
These peptides were not retainedusing the C18-MS system