5NFL:
reference: Sinorhizobium meliloti YrbA binds divalent metal cations using two conserved histidines., Roret T, Alloing G, Girardet JM, Perrot T, Dhalleine T, Couturier J, Frendo P, Didierjean C, Rouhier N, Biosci Rep. 2020 Oct 30;40(10). pii: 226508. doi: 10.1042/BSR20202956. PMID: 32970113

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