Fig. 4.

MS/MS spectra of glycosite-containing peptides (glycans were removed) and glycopeptides containing different glycans at the same glycosite. A, An MS/MS spectrum of a glycosite-containing peptide, AGPN*GTLFVADAYK, identified by SPEG method after PNGaseF treatment. B, An MS/MS spectrum of a glycopeptide, AGPN*GTLFVADAYK, containing HexNAc2Hex5. C, An MS/MS spectrum of an identified glycopeptide, AGPN*GTLFVADAYK, containing fucosylated glycan HexNAc 2 Hex5 Fuc1. The glycan cartoon structures are the most plausible structures based based on accurate masses and biosynthetic knowledge of N-linked glycans. The peptide with same backbone was observed in all three spectra. The oxonium ions represent the presence of the glycan structures. The reporter ion intensity represents a decrease in high mannose structures and an increase in fucosylation on the peptide AGPN*GTLFVADAYK in PC3 cells (116) compared with LNCaP cells (114, 115). * indicates deamidation of N because of PNGase F treatment.