1XG6:
reference: Single mutation at P1 of a chymotrypsin inhibitor changes it to a trypsin inhibitor: X-ray structural (2.15 A) and biochemical basis., Khamrui S, Dasgupta J, Dattagupta JK, Sen U, Biochim Biophys Acta 2005 Aug 31;1752(1):65-72. PMID: 16081330

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