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 structur e of the Ni site in the periplasmic Ni-binding protein NikA are presen ted. 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 w ith bonds averaging 2.06(2) Angstrom in length. Unlike UreE, another N i-binding protein, the Ni ligands in NikA are not largely imidazole li gands from histidine residues but are more likely derived from asparta te and glutamate carboxylate side chains.