2PGQ:
reference: Important role of the cys-191 cys-220 disulfide bond in thrombin function and allostery., Bush-Pelc LA, Marino F, Chen Z, Pineda AO, Mathews FS, Di Cera E, J Biol Chem. 2007 Sep 14;282(37):27165-70. Epub 2007 Jul 18. PMID: 17636263

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