Probing sialoglycans on fetal bovine fetuin with azido-sugars using glycosyltransferases

Sialic acids are negatively charged sugar residues commonly found on the terminal positions of most glycoproteins. They play important roles in the stability and solubility of these proteins. Due to their unique positioning, they also frequently act as receptors for various ligands, and therefore are involved in numerous cell-cell and cell-pathogen interactions. Here, using in vitro incorporation of clickable monosaccharides with various glycosyltransferases, we probed the sialoglycans on fetal bovine fetuin. The incorporated monosaccharides were detected with chemiluminescence via click chemistry in a format of western blotting. The results indicate that the non-reducing end Gal residues on both N- and O-glycans are fully sialylated, but the peptide-linked GalNAc residues in O-glycans are not. The presence of sialyl core-1 glycan was repeatedly confirmed by probing with α-2,3-sialyltransferases, N-acetylgalactosaminide α-2,6-sialyltransferases and a β-1,6-N-acetylglucosaminyltransferase that is specific for core-1 glycan. The results also suggest the presence of a minute amount of sialyl Tn antigen on the protein.