FIGURE 3.

The active site of ObcA in a ligand-free form. a, the active site is shown for ObcA in a ligand-free form with the nearby residues. Acetyl-CoA-interacting residues are indicated in gray, whereas metal-ligating and oxaloacetate-interacting residues (defined later) are colored in cyan. An octahedral geometry of the metal-coordinating shell is presented. Metal-coordinating water molecules (red sphere) and the metal ion (green sphere) are also indicated. b, the cavity of the active site of ObcA is shown as surface representation in a ligand-free form, with the N-domain (blue) and C-domain (gray). Water molecules in the metal-coordinating shell are indicated with red spheres. c, the metal-coordinating shell is presented, with water molecules and metal ions overlaid with an F_o − F_c map (4σ). d, a schematic drawing is presented for the interactions in the active site of ObcA in the ligand-free form. Dashed lines indicate possible hydrogen bonds within an interatomic distance of 3.6 Å. Note that Glu³⁴⁶ is 3.8 Å apart from the water molecule.