4KGR:
reference: Protein-like Tertiary Folding Behavior from Heterogeneous Backbones., Reinert ZE, Lengyel GA, Horne WS, J Am Chem Soc. 2013 Aug 28;135(34):12528-31. doi: 10.1021/ja405422v. Epub 2013, Aug 15. PMID: 23937097

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