4DG4:
reference: Presence versus absence of hydrogen bond donor Tyr-39 influences interactions of cationic trypsin and mesotrypsin with protein protease inhibitors., Salameh MA, Soares AS, Alloy A, Radisky ES, Protein Sci. 2012 Aug;21(8):1103-12. doi: 10.1002/pro.2097. Epub 2012 Jun 25. PMID: 22610453

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