2FR6:
reference: The 1.48 A Resolution Crystal Structure of the Homotetrameric Cytidine Deaminase from Mouse., Teh AH, Kimura M, Yamamoto M, Tanaka N, Yamaguchi I, Kumasaka T, Biochemistry. 2006 Jun 27;45(25):7825-7833. PMID: 16784234

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