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 is also 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 2,3/2,6-sialylated isomers, unambiguous identification of sialoglycopeptide isomers is still needed. Herein, an innovative strategy of glycosyltransferase labeling assisted mass spectrometry (GLAMS) were developed. After specific enzymatic labeling, oxonium ions from higher-energy C-trap dissociation (HCD) fragmentation of 2,3-sailoglycopeptides generate unique reporters to distinctly differentiate those of 2,6-sailoglycopeptide isomers. Using this strategy, a total of 1,138 linkage-specific sialoglycopeptides were successfully identified from 126 glycoproteins in human serum.