6GOP:
reference: (-)-Homosalinosporamide A and Its Mode of Proteasome Inhibition: An X-ray Crystallographic Study., Groll M, Nguyen H, Vellalath S, Romo D, Mar Drugs. 2018 Jul 19;16(7). pii: md16070240. doi: 10.3390/md16070240. PMID: 30029468

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