2NPH:
reference: Crystal structure of HIV-1 protease in situ product complex and observation of a low-barrier hydrogen bond between catalytic aspartates., Das A, Prashar V, Mahale S, Serre L, Ferrer JL, Hosur MV, Proc Natl Acad Sci U S A. 2006 Dec 5;103(49):18464-9. Epub 2006 Nov 20. PMID: 17116869

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