Hexose rearrangements upon fragmentation of N-glycopeptides and reductively aminated N-glycans.
Tandem mass spectrometry of glycans and glycoconjugates in protonated form is known to result in rearrangement reactions leading to internal residue loss. Here we studied the occurrence of hexose rearrangements in tandem mass spectrometry of N-glycopeptides and reductively aminated N-glycans by MALDI-TOF/TOF-MS/MS and ESI-ion trap-MS/MS. Fragmentation of proton adducts of oligomannosidic N-glycans of ribonuclease B that were labeled with 2-aminobenzamide and 2-aminobenzoic acid resulted in transfer of one to five hexose residues to the fluorescently tagged innermost N-acetylglucosamine. Glycopeptides from various biological sources with oligomannosidic glycans were likewise shown to undergo hexose rearrangement reactions, resulting in chitobiose cleavage products that have acquired one or two hexose moieties. Tryptic immunoglobulin G Fc-glycopeptides with biantennary N-glycans likewise showed hexose rearrangements resulting in hexose transfer to the peptide moiety retaining the innermost N-acetylglucosamine. Thus, as a general phenomenon, tandem mass spectrometry of reductively aminated glycans as well as glycopeptides may result in hexose rearrangements. This characteristic of glycopeptide MS/MS has to be considered when developing tools for de novo glycopeptide structural analysis.
Leiden University Medical Center, Biomolecular Mass Spectrometry Unit, Department of Parasitology, P.O. Box 9600, 2300 RC Leiden, The Netherlands. m.wuhrer@lumc.nl
Manfred
M
Wuhrer
Carolien A M
CA
Koeleman
André M
AM
Deelder
D000818:Animals; D002240:Carbohydrate Sequence; D002417:Cattle; D006020:Glycopeptides / Q000032:analysis* / Q000737:chemistry; D006601:Hexoses / Q000032:analysis / Q000737:chemistry*; D008969:Molecular Sequence Data; D011134:Polysaccharides / Q000032:analysis* / Q000737:chemistry; D012260:Ribonucleases / Q000032:analysis / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods*; D062367:ortho-Aminobenzoates
D006020:Glycopeptides; D006601:Hexoses; D011134:Polysaccharides; D062367:ortho-Aminobenzoates; C031385:anthranilic acid; D012260:Ribonucleases; C029600:ribonuclease B; C000219:anthranilamide