6PU8:
reference: Visualizing Tetrahedral Oxyanion Bound in HIV-1 Protease Using Neutrons: Implications for the Catalytic Mechanism and Drug Design., Kumar M, Mandal K, Blakeley MP, Wymore T, Kent SBH, Louis JM, Das A, Kovalevsky A, ACS Omega. 2020 May 14;5(20):11605-11617. doi: 10.1021/acsomega.0c00835., eCollection 2020 May 26. PMID: 32478251

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