A novel strategy for quantification of & alpha;2,3-and & alpha;2,6-linked sialic acids in sialylated glycoproteins

Sialic acid, a monosaccharide containing nine carbon atoms, is widely distributed in eukaryotic cells. The bound sialic acids are mainly present at the glycan ends of glycoconjugates via & alpha;2-3 or & alpha;2-6 glycosidic bonds, and alterations in their expression levels and linkage types are associated with the progress of many diseases and tumors. The present study provides a new strategy for quantification of & alpha;2,3- and & alpha;2,6-linked sialic acids in sialylated glycoproteins. In fact, quantification of & alpha;2,3-linked sialic acids were based on the difference of the bound sialic acids in the sample before and after treatment with & alpha;2-3 neuraminidase, whereas the & alpha;2,6-linked sialic acids were equal to the bound sialic acids in the & alpha;2-3 neuraminidase-treated sample. Subsequently, & alpha;2,3/6linked sialic acids in salivary glycoproteins from healthy volunteers and diabetic patients were quantified in accordance with this method. This work provides an accurate method for the quantification of & alpha;2,3- and & alpha;2,6linked sialic acids in the sialoglycoproteins, which is more instructive for understanding the biological roles of & alpha;2,3/6-linked sialic acid in sialoglycoproteins.