2OZK:
reference: Crystal Structure of a Monomeric Form of Severe Acute Respiratory Syndrome Coronavirus Endonuclease nsp15 Suggests a Role for Hexamerization as an Allosteric Switch., Joseph JS, Saikatendu KS, Subramanian V, Neuman BW, Buchmeier MJ, Stevens RC, Kuhn P, J Virol. 2007 Jun;81(12):6700-8. Epub 2007 Apr 4. PMID: 17409150

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