Spore-Encapsulating Glycosyltransferase Catalysis Tandem Reactions: Facile Chemoenzymatic Synthesis of Complex Human Glycans

Sialyl galactose (Sia-Gal) is one of the most abundant terminal motifs of oligosaccharides and is widely present in glycoconjugates and unconjugated glycans of animals. To investigate their function and biological roles, it is essential to obtain terminally structurally defined oligosaccharides. Herein, we describe a convenient and efficient strategy for the regioselective modification of glycans with terminal galactose (Gal) or Sia-Gal residues using immobilized enzymes. Galactosyltransferase (GalT) and sialyltransferase (ST) were encapsulated on the surface of yeast spores, which enabled facile assembly of diverse naturally occurring sialyl-galactosylated glycans, including human milk oligosaccharide, N-glycan biomarker, O-Man glycan, and O-GalNAc glycan. The utility of this strategy was further demonstrated by systematic construction of a panel of Core 2 O-GalNAc glycans.