Fig. 4. (A) Molecular surface representation of dGMII showing the position of the active site-bound Tris molecule and the MPD-binding site. (B) Molecular surface representation of dGMII with the GlcNAcMan₅GlcNAc₂ substrate modeled into the binding pocket. The substrate molecule is positioned into the binding pocket with α1,6-linked mannose M6 (shown in green) docked into the active site and β1,2-GlcNAc residue G3 (shown in black) placed in the MPD-binding site. Individual mannose residues of the substrate are colored according to the coloring scheme used in Figure 1A. (C) Representation of the sequential trimming of the α1,6- (M6) and α1,3-linked (M7) mannose residues. All molecular surface images were produced using GRASP (Nicholls et al., 1991).