One-Step Selective Labeling of Native Cell-Surface Sialoglycans by Exogenous α2,8-Sialylation

Exo-enzymatic glycan labeling strategies have emerged as versatile tools for efficient and selective installation of glycan terminal motifs onto live cell-surfaces. Through employing specific enzymes and nucleotide sugar probes, cells can be equipped with defined glyco-epitopes for modulating cell function or selective visualization and enrichment of glycoconjugates. Here, we identify Campylobacter jejuni sialyltransferase Cst-II I53S as a tool for cell-surface glycan modification, expanding the exo-enzymatic labeling toolkit to include installation of 2,8-disialyl epitopes. Labeling with Cst-II was achieved with biotin- and azide-tagged CMP-Neu5Ac derivatives on a model glycoprotein and on native sialylated cell-surface glycans across a panel of cell lines. The introduction of modified Neu5Ac derivatives onto cells by Cst-II was also retained on the surface for 6 h. By examining the specificity of Cst-II on cell surfaces, it was revealed that the 2,8-sialyltransferase primarily labeled N-glycans, with O-glycans labeled to a lesser extent, and there was an apparent preference for 2,3-linked sialosides. This approach thus broadens the scope of tools for selective exo-enzymatic labeling of native sialylated glycans and is highly amenable for construction of cell-based arrays.