Fig. 1: The crystal structure of ChR2 from Chlamydomonas reinhardtii (PDB: 6EID58).

Protonated retinal Schiff base (RSBH+) is depicted in yellow. The key residues of ion-conducting pore (magenta) and retinal binding pocket (green) with protonation states for polar residues are indicated by sticks (oxygen in red, nitrogen in blue, polar protons in white). Blue arrows show the ion permeation pathway.