Bacterial Glycosyltransferase-mediated Cell-surface Chemoenzymatic Glycan Editing: Methods and Applications

Chemoenzymatic glycan editing that modifies glycan structures directly on the cell surface has emerged as a complementary tool to metabolic oligosaccharide engineering. In this article, we report the discovery that three bacterial enzymes − Pasteurella multocida α2-3-sialyltransferase M144D mutant (Pm2,3ST-M144D), Photobacterium damsel α2-6-sialyltransferase (Pd2,6ST) and Helicobacter mustelae α1-2-fucosyltransferase (Hm1,2FT)− can serve as highly efficient tools for cell-surface glycan editing. Among these three enzymes, the two sialyltransferases were also found to be tolerant to large substituents introduced to the C-5 position of the cytidine monophosphate N-acetylneuraminic acid donor, including biotin and fluorescent dyes. Combining these enzymes with our previously discovered Helicobacter pylori α1-3-FT, we developed a live cell-based assay to probe host-cell glycan-mediated influenza A virus (IAV) infection including both wild-type and mutant strains of human H1N1 and H3N2 influenza subtypes. At high SiaNAcα2-6-Gal levels, the ability of a viral strain to induce the host cell death is positively correlated with the SiaNAcα2-6-Gal binding affinity of its haemagglutinin. Surprisingly, the creation of sLeX on the host cell surface via in situα1-3-Fuc editing also exacerbated the killing induced by several wild-type IAV strains as well as a mutant known as HK68-MTA. Structural alignment of HAs from the wild-type HK68 and HK68-MTA revealed the formation of a putative hydrogen bond between Trp222 of HA-HK68-MTA and the C-4 hydroxyl group of the α1-3-linked fucose of sLeX. This interaction is likely to be responsible for the better binding affinity of HA-HK68-MTA to sLeX and accordingly the enhanced host-cell killing compared with the wild-type HK68.