6CJQ:
reference: Ligand discrimination and gating in cyclic nucleotide-gated ion channels from apo and partial agonist-bound cryo-EM structures., Rheinberger J, Gao X, Schmidpeter PA, Nimigean CM, Elife. 2018 Jul 20;7. pii: 39775. doi: 10.7554/eLife.39775. PMID: 30028291

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