4TS5:
reference: Adenine Phosphoribosyltransferase from Sulfolobus solfataricus Is an Enzyme with Unusual Kinetic Properties and a Crystal Structure that Suggests It Evolved from a 6-Oxopurine Phosphoribosyltransferase., Jensen KF, Hansen MR, Jensen KS, Christoffersen S, Poulsen JC, Molgaard A, Kadziola A, Biochemistry. 2015 Mar 30. PMID: 25790177

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