Production of α-Galactosyl epitopes via combined use of two recombinant whole cells harboring UDP-galactose 4-epimerase and α-1,3-galactosyltransferase

α-Galactosyl epitopes (or α-Gal, oligosaccharides with a terminal Galα1,3Gal sequence) are a class of biologically important oligosaccharides in great demand in bulk quantities for basic and clinical studies on preventing hyperacute rejection in pig-to-primate organ xenotransplantaion. A truncated bovine α-1,3-galactosyltransferase, the key enzyme responsible for the biosynthesis of the terminal structure of α-Gal, was cloned and overexpressed previously. The acceptor specificity was further studied in the present paper, and lactose and galactose derivatives were found to be good acceptors. To develop a more proficient reaction process, we report herein an example of an efficient enzymatic synthesis of α-Gal oligosaccharides catalyzed by the combination of two recombinant Escherichia coli whole cells harboring the genes of a UDP-galactose 4-epimerase and the α-1,3-galactosyltransferase, respectively. Using lactosyl azide (LacN₃) as the acceptor for the glycosyltransferase, the combined use of the two recombinant cells efficiently produced α-Gal epitope Galα1,3LacN₃ in 60-68% yield.