| 4ICB: reference: Proline cis-trans isomers in calbindin D9k observed by X-ray crystallography., Svensson LA, Thulin E, Forsen S, J Mol Biol 1992 Feb 5;223(3):601-6. PMID: 1542107 |
This OCA 
Structure page
uses Jmol,
developed by the Jmol Development Team
(documentation).