Molecular mechanism of calcium inhibition in viral channelrhodopsins
Abstract
Abstract Viral channelrhodopsins (VCR1s) are giant-virus-encoded light-gated channels permeable to monovalent and divalent cations, including Na + and Ca 2+ ions, and inhibited by millimolar Ca 2+ concentrations. Here, we combine X-ray crystallography, time-resolved UV-vis spectroscopy, and ATR-FTIR spectroscopy to investigate molecular mechanisms of ion permeation and Ca 2+ -dependent inhibition in OLPVR1. An atomic resolution structure of OLPVR1 obtained in the presence of 10 mM CaCl 2 and 900 mM NaCl reveals a transient intracellular Ca 2+ binding site near T87 and T88, close to the retinal cofactor. Upon photoactivation, this Ca 2+ ion prevents a key rearrangement of the intracellular gate required for ion translocation, namely the flip of E44, thereby disrupting ion conduction. Instead, illumination leads to the accumulation of Na + ions between E44, S208 and the carbonyl oxygen of retinal-binding residue K204. Our findings reveal the molecular basis of Ca 2+ -dependent inhibition in VCR1s and provide a foundation for engineering enhanced tools for calcium optogenetics.
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Authors: Dmitrii Zabelskii, Sergey Bukhdruker, Gerrit H. U. Lamm, Siarhei Bukhalovich, Mako Aoyama, Vsevolod V. Sudarev, Alexander Kuzmin, Mikihiro Shibata, Kota Katayama, Hideki Kandori, Josef Wachtveitl, Ernst Bamberg, Valentin Gordeliy
Institutions: Moscow Institute of Physics and Technology, Université Grenoble Alpes, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Centre National de la Recherche Scientifique, Kanazawa University, Goethe University Frankfurt, Life Science Institute, CEA Grenoble, Institut de Biologie Structurale, Nagoya Institute of Technology, Max Planck Institute of Biophysics, European X-Ray Free-Electron Laser