2Y3Y:
reference: Holo-Ni(2+)Helicobacter pylori NikR contains four square-planar nickel-binding sites at physiological pH., Benini S, Cianci M, Ciurli S, Dalton Trans. 2011 Aug 21;40(31):7831-3. Epub 2011 Jul 4. PMID: 21725560

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).