α1 → 3‐Galactosyltransferase: the use of recombinant enzyme for the synthesis of α‐galactosylated glycoconjugates

We have reported the isolation and characterization of a bovine cDNA clone containing the complete coding sequence for UDP-Gal:Gal beta 1----4GlcNAc alpha 1----3-galactosyltransferase [Joziasse, D. H., Shaper, J. H., Van den Eijnden, D. H., Van Tunen, A. J. & Shaper, N. L. (1989) J. Biol. Chem. 264, 14290-14297]. Insertion of this cDNA clone into the genome of Autographa californica nuclear polyhedrosis virus (AcNPV) and subsequent infection of Spodoptera frugiperda (Sf9) insect cells with recombinant virus, resulted in high-level expression of enzymatically active alpha 1----3-galactosyltransferase. The expressed enzyme accounted for about 2% of the cellular protein; the corresponding specific enzyme activity was 1000-fold higher than observed in calf thymus, the tissue with the highest specific enzyme activity reported to date. The recombinant alpha 1----3-galactosyltransferase could be readily detergent-solubilized and subsequently purified by affinity chromatography on UDP-hexanolamine-Sepharose. The recombinant alpha 1----3-galactosyltransferase showed the expected preference for the acceptor substrate N-acetyllactosamine (Gal beta 1----4GlcNAc), and demonstrated enzyme kinetics identical to those previously reported for affinity-purified calf thymus alpha 1----3-galactosyltransferase [Blanken, W. M. & Van den Eijnden, D. H. (1985) J. Biol. Chem. 260, 12927-12934]. In pilot studies, the recombinant enzyme was examined for the ability to synthesize alpha 1----3-galactosylated oligosaccharides, glycolipids and glycoproteins. By a combination of 1H-NMR, methylation analysis, HPLC, and exoglycosidase digestion it was established that, for each of the model compounds, the product of galactose transfer had the anticipated terminal structure, Gal alpha 1----3Gal beta 1----4-R. Our results demonstrate that catalysis by recombinant alpha 1----3-galactosyltransferase can be used to obtain preparative quantities of various alpha 1----3-galactosylated glycoconjugates. Therefore, enzymatic synthesis using the recombinant enzyme is an effective alternative to the chemical synthesis of these biologically relevant compounds.