Comparison of Fe–ligand coordination geometry at the active site prior to O2 binding in some 2-His-1-carboxylate enzymes. (a) The APD–4NC complex structure, (b) the 4,5-PCD structure (PDB entry 1b4u
; Sugimoto et al., 1999), (c) HPCD (PDB entry 2iga
; Kovaleva & Lipscomb, 2007) and (d) the α-KG-dependent enzyme clavaminate synthase (CAS-α-KG-PCV; PDB entry 1drt
; Zhang et al., 2000). Schematic representations of the Fe-coordination scheme are shown in the middle and simplified representations showing Fe coordination with two O− anions from the carboxylic side chain of the Glu residue and a hydroxyl substituent of the bound ligand are shown at the bottom.