FIG 6.

NanoLC-MS/MS analysis of Δmmp0352 mutant pilin tryptic/Asp-N-glycopeptides. (a) MS/MS spectrum of the doubly protonated glycopeptide ion at m/z 693.3 corresponding to ⁵²DATSQMSNITD⁶² with a single GalNAc (◼). The same peptide was observed with no GalNAc residues attached (data not shown). (b) MS/MS spectrum of the doubly protonated glycopeptide ion at m/z 949.9 corresponding to ³⁴QITNSTNQTTQALA⁴⁷ modified with two GalNAc residues. The same peptide was also observed with 0 or 1 GalNAc modification (data not shown). Both MS/MS spectra are complicated by the strong loss of ammonia (−17 Da) and water (−18 Da) from the major fragment ions. Nevertheless, there is sufficient evidence in these spectra to confirm that these peptides are modified with one and two GalNAc residues, respectively.