4S2R:
reference: Crystal structure of X-prolyl aminopeptidase from Caenorhabditis elegans: A cytosolic enzyme with a di-nuclear active site., Iyer S, La-Borde PJ, Payne KA, Parsons MR, Turner AJ, Isaac RE, Acharya KR, FEBS Open Bio. 2015 Apr 2;5:292-302. doi: 10.1016/j.fob.2015.03.013. eCollection , 2015. PMID: 25905034

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