Current Methods for the Characterization of O-Glycans

Glycosylation is crucial in cellular metabolism and survival. Of interest is the role of N-linked and O-linked glycans in disease states. Robust analytical methods must be defined to identify suitable glycan biomarkers and glyco-therapeutics. Fortunately, in N-glycan analysis, a universal enzyme exists to deglycosylate a variety of common-core structures from proteins for analysis using mass spectrometric and fluorescence techniques. Unfortunately, for their O-linked counterparts, no such enzyme exists. Furthermore, O-glycan heterogeneity is vast due to the lack of a common glycan core, making analysis challenging. As such, chemical methods are used to liberate O-glycans, however, often to the detriment of the glycan's structure due to "peeling" reactions. This review outlines approaches for O-glycan release and downstream glycomic and glycoproteomic analysis.