Figure 2
From: Classification of Tandem Mass Spectra for Identification of N- and O-linked Glycopeptides
Spectral differences between O- and N-glycopeptides in the oxonium ion region.
The intensities of 9 different oxonium ions normalized by the intensity of HexNAc ion at 204 are depicted. The plotted ions are as follows: (A) Hex—H2O ion at 145, (B) Hex ion at 163, (C) Hex2 ion at 325, (D) HexNAc internal fragment ion at 138, (E) HexNAc—2 H2O ion at 168, (F) HexNAc—H2O ion at 186, (G) HexHexNAc ion at 366, (H) Neu5Ac—H2O ion at 274 and (I) Neu5Ac ion at 292. There are clear differences between the two types of glycosylation in terms of their oxonium ion intensities. These differences are more pronounced for some of these ions. In particular, normalized intensity of 186 is significantly higher in O-linked spectra. The other two HexNAc ions are however higher in the N-linked spectra. Furthermore, sialic acid residues have a greater share in the oxonium ion intensities of O-linked spectra while Hex oxonium ions are generally higher in the N-linked spectra. These differences, fed into a machine learning algorithm, can help classify the spectra and predict the glycosylation type.
