The light-gated ion channel channelrhodopsin 2 (ChR2) from Chlamydomonas reinhardtii is a major optogenetic tool. Photon absorption starts a well-characterized photocycle, but the structural basis for the regulation of channel opening remains unclear. We present high-resolution structures of ChR2 and the C128T mutant, which has a markedly increased open-state lifetime. The structure reveals two cavities on the intracellular side and two cavities on the extracellular side. They are connected by extended hydrogen-bonding networks involving water molecules and side-chain residues. Central is the retinal Schiff base that controls and synchronizes three gates that separate the cavities. Separate from this network is the DC gate that comprises a water-mediated bond between C128 and D156 and interacts directly with the retinal Schiff base. Comparison with the C128T structure reveals a direct connection of the DC gate to the central gate and suggests how the gating mechanism is affected by subtle tuning of the Schiff base's interactions.

ELI Beamlines Institute of Physics Czech Academy of Sciences 18221 Prague Czech Republic

European Synchrotron Radiation Facility 38027 Grenoble France

Institut de Biologie Structurale Jean Pierre Ebel Université Grenoble Alpes Commissariat à l'Energie Atomique et aux Energies Alternatives CNRS Grenoble France

Institut für Physikalische Biologie Heinrich Heine Universität Düsseldorf Düsseldorf Germany

Institute of Complex Systems ICS 6 Structural Biochemistry Research Centre Juelich Juelich Germany

Institute of Crystallography University of Aachen Aachen Germany

Max Planck Institute of Biophysics Frankfurt am Main Germany

Moscow Institute of Physics and Technology Dolgoprudny Russia

Science. 2017 Nov 24;358(6366):1000-1001. doi: 10.1126/science.aar2299. PubMed

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