Identifying Sialylation Linkages at the Glycopeptide Level by Glycosyltransferase Labeling Assisted Mass Spectrometry (GLAMS)

Precise
assignment of sialylation linkages at the glycopeptide
level is of importance in bottom-up glycoproteomics and an indispensable
step to understand the function of glycoproteins in pathogen–host
interactions and cancer progression. Even though some efforts have
been dedicated to the discrimination of α2,3/α2,6-sialylated
isomers, unambiguous identification of sialoglycopeptide isomers is
still needed. Herein, we developed an innovative glycosyltransferase
labeling assisted mass spectrometry (GLAMS) strategy. After specific
enzymatic labeling, oxonium ions from higher-energy C-trap dissociation
(HCD) fragmentation of α2,3-sailoglycopeptides then generate
unique reporters to distinctly differentiate those of α2,6-sailoglycopeptide
isomers. With this strategy, a total of 1236 linkage-specific sialoglycopeptides
were successfully identified from 161 glycoproteins in human serum.