Figure 1. Photocycle model of channelrhodopsin.

Schematic model of the C1C2 photocycle. Superscript of each reaction intermediate (P₁⁽⁵²⁰⁾, P₂⁽³⁹⁰⁾, P₃⁽⁵²⁰⁾, P₄⁽⁴⁸⁰⁾) indicates the wavelength of maximum absorption. Open/close states of the channel pore and the proposed model of the retinal and protonation of Schiff base are indicated. The time range in which the P₁–P₃ intermediates were observed in the spectroscopic studies in solution is shown.

Figure 1—figure supplement 1. Sequence alignment of channelrhodopsin (ChR) variants.

Amino acid sequences of major variants of ChRs are shown. Conserved residues are highlighted in gray and red. The residues in red indicate important residues for the initial trigger revealed by the current study. The D–C pair is indicated by green arrow heads.