Glycosyltransferases in chemo-enzymatic synthesis of oligosaccharides.

Many oligosaccharides are not commercially available, which limits studies focused on elucidation of glycan functions; therefore chemo-enzymatic methods to synthesize them can be very useful. Here, we describe the procedure to synthesize the Galα1-3GalNAcβ1-4GlcNAcβ-R (Gal-LDN) moiety, containing the Galα1-3GalNAc epitope found on the parasitic helminth Haemonchus contortus. An acceptor substrate providing a terminal N-acetylglucosamine was prepared by coupling the fluorescent hydrophobic aglycon, 2,6-diaminopyridine (DAP), to N,N'-diacetylchitobiose. By the subsequent action of recombinant Caenorhabditis elegans β1,4-N-acetylgalactosaminyltransferase the substrate was efficiently converted to GalNAcβ1-4GlcNAcβ-R (LDN-R). Since no recombinant α1,3-galactosyltransferase has been described that acts on terminal βGalNAc, we used bovine α1,3-galactosyltransferase to obtain a partial conversion of LDN-R to the Gal-LDN antigen. This method can be applied to synthesize any oligosaccharide, provided that specific glycosyltransferases are available, or related enzymes that can be pushed to elongate the selected acceptor.