Figure 3.

The donor nucleotide sugar binding site in B3GNT2.A, The structure of SeMet-B3GNT2:UDP:Mg²⁺ showing the dimer in the asymmetric unit (cyan and gray cartoons). The UDP (magenta, stick mode) and Mg²⁺ (green sphere) in the active site and the disulfide bonds (yellow spheres), the N-terminus of the structure (blue spheres), and C-terminus (red spheres) are shown. The proposed membrane bound form of the SeMet-B3GNT2:UDP:Mg²⁺ dimer is depicted with a diagrammatic representation of the “stem region” (residues 29–51, cyan and gray arcs) and NH₂-terminal transmembrane anchor (residues 8–28, cyan and grayrectangles) for the full-length enzyme found in vivo. B, The structure of the SeMetB3GNT2:UDP:Mg²⁺monomer in cartoon mode with secondary structural elements colored as follows: helices (pale gray), sheets (orange), and loops (cyan). The secondary structure elements are numbered sequentially. The active site UDP, the Mg²⁺ ion, the N-and C- termini are shown and colored as in panel A. The N-glycans attached to N127 and N219 are also shown and colored yellow.