3SHJ:
reference: Hydroxyureas as Noncovalent Proteasome Inhibitors., Gallastegui N, Beck P, Arciniega M, Huber R, Hillebrand S, Groll M, Angew Chem Int Ed Engl. 2011 Nov 21. doi: 10.1002/anie.201106010. PMID: 22105886

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