2KSY:
reference: Structure determination of the seven-helix transmembrane receptor sensory rhodopsin II by solution NMR spectroscopy., Gautier A, Mott HR, Bostock MJ, Kirkpatrick JP, Nietlispach D, Nat Struct Mol Biol. 2010 Jun;17(6):768-74. Epub 2010 May 30. PMID: 20512150

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