6MQW:
reference: Mimicking Microbial Rhodopsin Isomerization in a Single Crystal., Ghanbarpour A, Nairat M, Nosrati M, Santos EM, Vasileiou C, Dantus M, Borhan B, Geiger JH, J Am Chem Soc. 2018 Dec 22. doi: 10.1021/jacs.8b12493. PMID: 30580520

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