Figure 5.

CAIR, SAICAR, and SAICAR-Mg²⁺ bound in the SAICARs active site. A, the active site hydrogen bond network is shown here for SAICAR (green sticks), and the CAIR molecule (yellow sticks) from the second monomer is shown in superposition. The imidazole molecule is shown as magenta sticks. B, the active site hydrogen bond network is shown here for SAICAR-Mg²⁺ (green sticks and green sphere). The active site residues involved in direct (black dashed lines) or water-mediated, imidazole-mediated, and magnesium-mediated (cyan dashed lines) hydrogen bonds are shown as pale blue sticks. Residue Phe-129 that stacks with the imidazole molecule or forms a π-stacking interaction (orange dashed line) with a ligand-bound water molecule is also shown. C, refined 2F_o – F_c electron density maps for CAIR, SAICAR, and SAICAR-Mg²⁺ contoured at 1σ are shown left to right, respectively.