Volume 61, Issue 2 e202111930
Research Article

A Unified View on Varied Ultrafast Dynamics of the Primary Process in Microbial Rhodopsins

Dr. Chun-Fu Chang

Dr. Chun-Fu Chang

Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan

Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-Ku, Tokyo, 113-0033 Japan

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Dr. Hikaru Kuramochi

Dr. Hikaru Kuramochi

Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan

Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan

PRESTO (Japan) Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama, 332-0012 Japan

Present address: Research Center of Integrative Molecular Systems, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki, 444-8585 Japan

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Dr. Manish Singh

Dr. Manish Singh

Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Showa-Ku, Nagoya, Aichi, 466-8555 Japan

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Dr. Rei Abe-Yoshizumi

Dr. Rei Abe-Yoshizumi

Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Showa-Ku, Nagoya, Aichi, 466-8555 Japan

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Prof. Tatsuya Tsukuda

Prof. Tatsuya Tsukuda

Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-Ku, Tokyo, 113-0033 Japan

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Prof. Hideki Kandori

Prof. Hideki Kandori

Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Showa-Ku, Nagoya, Aichi, 466-8555 Japan

OptoBioTechnology Research Center, Nagoya Institute of Technology, Showa-Ku, Nagoya, Aichi, 466-8555 Japan

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Prof. Dr. Tahei Tahara

Corresponding Author

Prof. Dr. Tahei Tahara

Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan

Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan

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First published: 20 October 2021
Citations: 20

Graphical Abstract

Varied excited-state relaxation dynamics observed in the primary photoreaction of microbial rhodopsins are the ground-state heterogeneity arising from the acid-base equilibrium of the amino acid residue acting as the counterion of a protonated retinal Schiff base chromophore.

Abstract

All-trans to 13-cis photoisomerization of the protonated retinal Schiff base (PRSB) chromophore is the primary step that triggers various biological functions of microbial rhodopsins. While this ultrafast primary process has been extensively studied, it has been recognized that the relevant excited-state relaxation dynamics differ significantly from one rhodopsin to another. To elucidate the origin of the complicated ultrafast dynamics of the primary process in microbial rhodopsins, we studied the excited-state dynamics of proteorhodopsin, its D97N mutant, and bacteriorhodopsin by femtosecond time-resolved absorption (TA) spectroscopy in a wide pH range. The TA data showed that their excited-state relaxation dynamics drastically change when pH approaches the pKa of the counterion residue of the PRSB chromophore in the ground state. This result reveals that the varied excited-state relaxation dynamics in different rhodopsins mainly originate from the difference of the ground-state heterogeneity (i.e., protonation/deprotonation of the PRSB counterion).

Conflict of interest

The authors declare no conflict of interest.

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