Enhanced Detection and Identification of Glycopeptides in Negative Ion Mode Mass Spectrometry

A combined mass spectrometry (MS) and tandem mass spectrometry (MS/MS) approach implemented with matrix assisted laser desorption ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI FTICR MS) m the negative ion mode is described for enhanced glycopeptide detection and MS/MS analysis Positive ion mode MS analysis is widely used for glycopeptide characterization, but the analyses are hampered by potential charge-induced fragmentation of the glycopeptides and poor detection of the glycopeptides harboring sialic acids Furthermore, tandem MS analysis (MS/MS.,) via collision induced dissociation (CID) of glycopeptides in the positive ion mode predominantly yields glycan fragmentation with minimal information to verify the comic cling peptide moiety In this study, glycoproteins sui h as, bovine lactoferrin (b-LF) for N-glycosylation and kappa casein (k-CN) for O-glycosylation were analyzed in both the positive-and negative ion modes after digestion with bead-im mobilized Pronase For the b-LF analysis, 44 potential N linked glycopeptides were detected in the positive ion mode while 61 potential N-linked glycopeptides were detected in the negative ion mode By the same token, more O-linked glycopeptides mainly harboring sialic acids from k CN were detected in the negative ion mode The enhanced glycopeptide detection allowed improved site specific analysts of protein glycosylation and superior to positive ion mode detection Overall, the negative ion mode approach is aimed toward enhanced N and 0 linked glycopeptide detection and to serve as a complementary tool to positive ion mode MS/MS analysis