4K4P:
reference: Crystallographic Fragment Based Drug Discovery: Use of a Brominated Fragment Library Targeting HIV Protease., Tiefenbrunn T, Forli S, Happer M, Gonzalez A, Tsai Y, Soltis M, Elder JH, Olson AJ, Stout CD, Chem Biol Drug Des. 2013 Sep 2. doi: 10.1111/cbdd.12227. PMID: 23998903

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