Molecular properties of a DTD channelrhodopsin from <i>Guillardia theta</i>

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Author(s)

    • Yamauchi Yumeka
    • Department of Life Science and Applied Chemistry, Nagoya Institute of Technology
    • Konno Masae
    • Department of Life Science and Applied Chemistry, Nagoya Institute of Technology|OptoBioTechnology Research Center, Nagoya Institute of Technology
    • Ito Shota
    • Department of Life Science and Applied Chemistry, Nagoya Institute of Technology
    • Tsunoda Satoshi P.
    • Department of Life Science and Applied Chemistry, Nagoya Institute of Technology|OptoBioTechnology Research Center, Nagoya Institute of Technology|PRESTO, Japan Science and Technology Agency
    • Inoue Keiichi
    • Department of Life Science and Applied Chemistry, Nagoya Institute of Technology|OptoBioTechnology Research Center, Nagoya Institute of Technology|PRESTO, Japan Science and Technology Agency|Frontier Research Institute for Material Science, Nagoya Institute of Technology
    • Kandori Hideki
    • Department of Life Science and Applied Chemistry, Nagoya Institute of Technology|OptoBioTechnology Research Center, Nagoya Institute of Technology

Abstract

<p>Microbial rhodopsins are membrane proteins found widely in archaea, eubacteria and eukaryotes (fungal and algal species). They have various functions, such as light-driven ion pumps, light-gated ion channels, light sensors and light-activated enzymes. A light-driven proton pump bacteriorhodopsin (BR) contains a DTD motif at positions 85, 89, and 96, which is unique to archaeal proton pumps. Recently, channelrhodopsins (ChRs) containing the DTD motif, whose sequential identity is ~20% similar to BR and to cation ChRs in <i>Chlamydomonas reinhardtii</i> (<i>Cr</i>CCRs), were found. While extensive studies on ChRs have been performed with <i>Cr</i>CCR2, the molecular properties of DTD ChRs remain an intrigue. In this paper, we studied a DTD rhodopsin from <i>G. theta</i> (<i>Gt</i>CCR4) using electrophysiological measurements, flash photolysis, and low-temperature difference FTIR spectroscopy. Electrophysiological measurements clearly showed that <i>Gt</i>CCR4 functions as a light-gated cation channel, similar to other <i>G. theta</i> DTD ChRs (<i>Gt</i>CCR1-3). Light-driven proton pump activity was also suggested for <i>Gt</i>CCR4. Both electrophysiological and flash photolysis experiments showed that channel closing occurs upon reprotonation of the Schiff base, suggesting that the dynamics of retinal and channels are tightly coupled in <i>Gt</i>CCR4. From Fourier transform infrared (FTIR) spectroscopy at 77 K, we found that the primary reaction is an all-<i>trans</i> to a 13-<i>cis</i> photoisomerization, like other microbial rhodopsins, although perturbations in the secondary structure were much smaller in <i>Gt</i>CCR4 than in <i>Cr</i>CCR2.</p>

Journal

  • Biophysics and Physicobiology

    Biophysics and Physicobiology 14(0), 57-66, 2017

    The Biophysical Society of Japan

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