4GYC:
reference: Ground state structure of D75N mutant of sensory rhodopsin II in complex with its cognate transducer., Ishchenko A, Round E, Borshchevskiy V, Grudinin S, Gushchin I, Klare JP, Balandin T, Remeeva A, Engelhard M, Buldt G, Gordeliy V, J Photochem Photobiol B. 2013 Jun 5;123:55-8. doi:, 10.1016/j.jphotobiol.2013.03.008. Epub 2013 Mar 29. PMID: 23619282

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