Fig. 2: Details of high-resolution AxqNOR and its comparison with other family members GsqNOR, NmqNOR, PacNOR, and E. coli cytochrome bo₃.

a Binuclear center of AxqNOR with Fe_B coordinated by His486, His537, and His538 and µ-oxo bridge O. Iron atoms and water molecules shown as orange and red spheres, respectively. Hydrogen bonds and metal coordinating bonds are shown as black and red dashed lines, respectively. This scheme is used throughout the figure. b Binuclear center of GsqNOR (PDB ID: 3AYG) with a penta-coordinated zinc center. Glu512 is not bonded to ligands of the non-heme iron center. Zn is shown as a gray sphere. c Binuclear center of AxqNOR with the density map contoured to a sigma level of 0.034, except for that corresponding to Glu490 and water molecules which is contoured at 0.020. d Binuclear center of NmqNOR (PDB ID: 6L3H) with a non-heme Fe_B, which is coordinated by three histidine residues and Glu494. Fe ions are shown as orange spheres. e Binuclear center of PacNOR (PDB: 3O0R) with a penta-coordinated Fe_B center. Glu211 is bonded to a non-heme iron center. Water molecule W1 is bound to Fe_B and heme b₃ Fe. f Binuclear center of E. coli cytochrome bo₃ (PDB: 7N9Z) with a tri-coordinated Cu center. Cu is shown as a blue sphere.