Fold recognition study of α3-galactosyltransferase and molecular modeling of the nucleotide sugar-binding domain

The structure and fold of the enzyme responsible for the biosynthesis of the xenotransplantation antigen, namely pig α3 galactosyltransferase, has been studied by means of computational methods. Secondary structure predictions indicated that α3-galactosyltransferase and related protein family members, including blood group A and B transferases and Forssman synthase, are likely to consist of alternating α-helices and β-strands. Fold recognition studies predicted that α3-galactosyltransferase shares the same fold as the T4 phage DNA-modifying enzyme β-glucosyltransferase. This latter enzyme displays a strong structural resemblance with the core of glycogen phosphorylase b. By using the three-dimensional structure of β-glucosyltransferase and of several glycogen phosphorylases, the nucleotide binding domain of pig α3-galactosyltransferase was built by knowledge-based methods. Both the UDP-galactose ligand and a divalent cation were included in the model during the refinement procedure. The final three-dimensional model is in agreement with our present knowledge of the biochemistry and mechanism of α3-galactosyltransferases.