5DRE:
reference: Evaluation of the Catalytic Contribution from a Positioned General Base in Ketosteroid Isomerase., Lamba V, Yabukarski F, Pinney M, Herschlag D, J Am Chem Soc. 2016 Jul 13. PMID: 27410422

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