Natural and recombinant A and B gene encoded glycosyltransferases

The human blood group A and B synthesizing enzymes are glycosyltransferases that catalyse the transfer of a monosaccharide residue from UDP-GalNAc and UDP-Gal donors, respectively, to alpha Fuc 1,2-Gal terminated blood group H acceptors. Extensive investigations of their substrate specificity and ph ysical properties have been carried out since their initial discovery. Thes e studies demonstrated a rigid specificity for the acceptor structure, cros sover in donor specificity and immunological similarity along with chromato graphic differences. Cloning of the enzymes has shown that they are highly homologous, differing in only four of their 354 amino acids. Changing the r esidues Argt76 --> Gly, Gly235 --> Ser, Leu266 --> Met and Gly 268 --> Ala converts the enzyme specificity from blood group A to blood group B glycosy ltransferase. Structure function investigations have been carried out by sy stematic interchange and modification of these four critical amino acids. T hese studies have shown that donor specificity is attributed to the last tw o amino acids. Mutants have also been produced with greatly enhanced turnov er rates as well as hybrid A/B enzymes that catalyse both reactions efficie ntly.