High-efficiency labeling of sialylated glycoproteins on living cells

Sialic acid–containing cell-surface glycoproteins can be chemically labeled with a biotin tag under mild conditions. The method is highly efficient and uses commercially available reagents; it should be useful for studying glycoprotein trafficking as well as in glycoproteomics applications. We describe a simple method for efficiently labeling cell-surface sialic acid–containing glycans on living animal cells. The method uses mild periodate oxidation to generate an aldehyde on sialic acids, followed by aniline-catalyzed oxime ligation with a suitable tag. Aniline catalysis dramatically accelerates oxime ligation, allowing use of low concentrations of aminooxy-biotin at neutral pH to label the majority of cell-surface sialylated glycoproteins while maintaining high cell viability.