1GM9:
reference: Crystal structures of penicillin acylase enzyme-substrate complexes: structural insights into the catalytic mechanism., McVey CE, Walsh MA, Dodson GG, Wilson KS, Brannigan JA, J Mol Biol. 2001 Oct 12;313(1):139-50. PMID: 11601852

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