Exo-enzymatic glycan labeling strategies
have emerged
as versatile
tools for efficient and selective installation of terminal glyco-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 identifyCampylobacter jejunisialyltransferase Cst-II I53S as a tool for cell surface glycan modification,
expanding the exo-enzymatic labeling toolkit to include installation
of α2,8-disialyl epitopes. Labeling with Cst-II was achieved
with biotin- and azide-tagged CMP-Neu5Ac derivatives on a model glycoprotein
and 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 α2,8-sialyltransferase
primarily labeled N-glycans, with O-glycans labeled to a lesser extent,
and there was an apparent preference for α2,3-linked sialosides
on cells. This approach thus broadens the scope of tools for selective
exo-enzymatic labeling of native sialylated glycans and is highly
amenable for the construction of cell-based arrays.