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. 2012 Nov 19;7(11):e50018. doi: 10.1371/journal.pone.0050018

Figure 1. Simplified photocycle and ChR2 single serine mutation model.

Figure 1

(A) Simple four-state model of the channelrhodopsin-2 photocycle. The two nonconducting states consist of a dark-adapted (C1) and desensitized (C2) state. The conducting states represent an early conducting state (O1) and a late conducting state (O2). Blue arrows represent illumination with blue light. (B) Structural model of ChR2 based on the channelrhodopsin chimera C1C2 (PDB entry: 3UG9) highlighting the locations of serine mutations. Three residues (black) had highly reduced photocurrents, while 5 mutations showed changes in pore size, permeability, and/or kinetics (orange). Residue S136 is shown in purple. The retinal chromophore, which is covalently bound to K257, is shown in yellow. This figure was prepared using Visual Molecular Dynamics [37]. (C) Sequence comparison of transmembrane domains between bacteriorhodopsin and channelrhodopsin-2. Residues that correspond to serine mutations are highlighted in orange. Adapted from [9].