Chemoenzymatic Synthesis of 6-Sulfo Lewis X-Related Glycans for Probing Their Ligand-Binding Proteins

6-sulfo Lewis x-related glycan epitopes, including 6-sulfo Lewis x and its sialylated form, sialyl 6-sulfo Lewis x, constitute an important class of carbohydrate determinants that are widely expressed in human cells. Elucidating the biological roles and structure-function relationships of these glycans has attracted considerable attention, as a substantial body of literatures suggest that 6-sulfo Lewis x-related glycans regulate numerous physiological and pathological processes through interactions with their glycan-binding proteins. However, the synthesis of intact complex glycans processing 6-sulfo Lewis x or sialyl 6-sulfo Lewis x glycan epitopes is much more difficult, as the incorporation of the sulfate group and sialic acid residue introduces additional complexity to the oligosaccharide synthesis. Here, we present a chemoenzymatic synthetic strategy for the efficient synthesis of complex N-glycans and O-glycans bearing 6-sulfo Lewis x-related epitopes. By screening a microarray prepared with this glycan library, we systematically probed their binding specificities with many important human glycan-binding proteins. The results provide an insightful understanding of the structure-function relationships of this important class of glycan structures.