Titanium dioxide enrichment of sialic acid-containing glycopeptides

Glycosylation is one of the many post-translational protein modifications that regulate several biological processes of proteins and lipids. In particular aberrant sialylation, at the terminal position of the glycan structures of cell surface proteins, occurs in numerous diseases such as cancer metastasis and viral infections. Methodological improvements in the sample preparation and analysis currently enable the detailed identification of the glycosylation sites and glycan structure characterization. In this context, the aim of this chapter is to describe a methodology to identify the glycosylation site of N-linked sialylated glycoproteins. The method relies on the specificity of titanium dioxide affinity chromatography to isolate sialic acid-containing glycopeptides. After enzymatic release of the glycans, the enriched sialylated glycopeptides are analyzed by mass spectrometry. This strategy was applied to a crude membrane fraction of EGF-stimulated HeLa cells metabolically labeled with SILAC enabling both qualitative and quantitative analyses of sialoglycopeptides.