Red-Tuning of the Channelrhodopsin Spectrum Using Long Conjugated Retinal Analogues

Yi Chung Shen, Toshikazu Sasaki, Take Matsuyama, Takahiro Yamashita, Yoshinori Shichida, Takashi Okitsu, Yumiko Yamano, Akimori Wada, Toru Ishizuka, Hiromu Yawo, Yasushi Imamoto

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3 Citations (Scopus)

Abstract

As optogenetic studies become more popular, the demand for red-shifted channelrhodopsin is increasing, because blue-green light is highly scattered or absorbed by animal tissues. In this study, we developed a red-shifted channelrhodopsin by elongating the conjugated double-bond system of the native chromophore, all-trans-retinal (ATR1). Analogues of ATR1 and ATR2 (3,4-didehydro-retinal) in which an extra C=C bond is inserted at different positions (C6-C7, C10-C11, and C14-C15) were synthesized and introduced into a widely used channelrhodopsin variant, C1C2 (a chimeric protein of channelrhodopsin-1 and channelrhodopsin-2 from Chlamydomonas reinhardtii). C1C2 bearing these retinal analogues as chromophores showed broadened absorption spectra toward the long-wavelength side and photocycle intermediates similar to the conducting state of channelrhodopsin. However, the position of methyl groups on the retinal polyene chain influenced the yield of the pigment, absorption maximum, and photocycle pattern to a variable degree. The lack of a methyl group at position C9 of the analogues considerably decreased the yield of the pigment, whereas a methyl group at position C15 exhibited a large red-shift in the absorption spectra of the C1C2 analogue. Expansion of the chromophore binding pocket by mutation of aromatic residue Phe265 to Ala improved the yield of the pigment bearing elongated ATR1 analogues without a great alteration of the photocycle kinetics of C1C2. Our results show that elongation of the conjugated double-bond system of retinal is a promising strategy for improving the ability of channelrhodopsin to absorb long-wavelength light passing through the biological optical window.

Original languageEnglish
Pages (from-to)5544-5556
Number of pages13
JournalBiochemistry
Volume57
Issue number38
DOIs
Publication statusPublished - 2018 Sep 25

ASJC Scopus subject areas

  • Biochemistry

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    Shen, Y. C., Sasaki, T., Matsuyama, T., Yamashita, T., Shichida, Y., Okitsu, T., Yamano, Y., Wada, A., Ishizuka, T., Yawo, H., & Imamoto, Y. (2018). Red-Tuning of the Channelrhodopsin Spectrum Using Long Conjugated Retinal Analogues. Biochemistry, 57(38), 5544-5556. https://doi.org/10.1021/acs.biochem.8b00583