Sensitive analysis of glycans and glycoproteins: Quantitative glycomics and glycoproteomics by LC-MS/MS

Glycosylation is one of the most common and essential post-translational modifications (PTMs), which has been reported that more than 50% mammalian proteins are glycosylated. In recent decades, the ubiquitous glycosylation has been considered as one of the most important proteins post translational modifications, due to its significant impact on protein properties, such as conformation and solubility. Furthermore, glycosylation plays a prominent role in many biological functions, such as cell-cell signaling, protein degradation and immune response. Recently, protein glycosylation was reported as a critical element in diseases, including cancer, autoimmune diseases, and inflammatory diseases. It has been universally accepted that protein glycosylation can be classified into two types according to the linkages to proteins: N-linked glycosylation and O-linked glycosylation. Both N- and O-glycans are produced by different competing enzymatic processes without templates. Other than glycans present in glycoproteins, there are various glycoconjugates, such as glycolipids, proteoglycans and free oligosaccharides, demonstrating the large diversity of glycan-related species. Despite the significance of glycosylation, the characterization of glycan and glycopeptide remain challenging since the LC-MS/MS based analysis of glycan and glycopeptide is hindered by the microheterogeneity, the low ionization efficiency and the relatively low abundance of glycan and glycopeptide. The studies presented here, including a carbon-based purification method, chemical derivatization strategies on sialoglycopeptides, and utilization of O-glycoproteases, focus on resolving these problems.

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