An X-ray absorption spectroscopic structural investigation of the nickel site in Escherichia coli NikA protein

The results of an X-ray absorption spectroscopic study of the structure of the Ni site in the periplasmic Ni-binding protein NikA are presented. These studies demonstrate that the Ni site is 6 or 7-coordinate, with the ligand environment composed of 6 or 7 O- or N-donor ligands with bonds averaging 2.06(2) Angstrom in length. Unlike UreE, another Ni-binding protein, the Ni ligands in NikA are not largely imidazole ligands from histidine residues but are more likely derived from aspartate and glutamate carboxylate side chains.