Structure of bovine α‐1,3‐galactosyltransferase and its complexes with UDP and DPGal inferred from molecular modeling

A homology model of alpha-1,3-galactosyltransferase (alpha-1,3-GalT), the retaining enzyme responsible for the formation of alpha-galactosyl epitopes, has been developed by means of molecular modeling using the SpsA glycosyltransferase structure. A protein-ligand docking approach was used to model alpha-1,3-GalT complexed with UDP and UDP-Gal. The comparison of structural features found in the alpha-1,3-GalT homology model with available structural data on this class of enzymes revealed similarities in the UDP-binding pocket. In the predicted structure of the complexes, the pyrophosphate interacts with the DVD motif (Asp-225, Val-226, and Asp-227) of alpha-1,3-GalT through the Mn(2+) cation. The uridine part of the UDP binds into the well-defined cavity that consists of Phe-134, Tyr-139, Ile-140, Val-136, Arg-194, Arg-202, Lys-209, Asp-173, His-218, and Thr-137 in a conformation that is generally observed in the crystal structures of other glycosyltransferase complexes.