2HBQ:
reference: A common allosteric site and mechanism in caspases., Scheer JM, Romanowski MJ, Wells JA, Proc Natl Acad Sci U S A. 2006 May 16;103(20):7595-600. Epub 2006 May 8. PMID: 16682620

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