Implications for the Light-Driven Chloride Ion Transport Mechanism of Nonlabens marinus Rhodopsin 3 by Its Photochemical Characteristics

Takashi Tsukamoto, Susumu Yoshizawa, Takashi Kikukawa, Makoto Demura, Yuki Sudo

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20 Citations (Scopus)


Several new retinal-based photoreceptor proteins that act as light-driven electrogenic halide ion pumps have recently been discovered. Some of them, called "NTQ" rhodopsins, contain a conserved Asn-Thr-Gln motif in the third or C-helix. In this study, we investigated the photochemical characteristics of an NTQ rhodopsin, Nonlabens marinus rhodopsin 3 (NM-R3), which was discovered in the N. marinus S1-08T strain, using static and time-resolved spectroscopic techniques. We demonstrate that NM-R3 binds a Cl- in the vicinity of the retinal chromophore accompanied by a spectral blueshift from 568 nm in the absence of Cl- to 534 nm in the presence of Cl-. From the Cl- concentration dependence, we estimated the affinity (dissociation constant, Kd) for Cl- in the original state as 24 mM, which is ca. 10 times weaker than that of archaeal halorhodopsins but ca. 3 times stronger than that of a marine bacterial Cl- pumping rhodopsin (C1R). NM-R3 showed no dark-light adaptation of the retinal chromophore and predominantly possessed an all-trans-retinal, which is responsible for the light-driven Cl- pump function. Flash-photolysis experiments suggest that NM-R3 passes through five or six photochemically distinct intermediates (K, L(N), O1, O2, and NM-R3′). From these results, we assume that the Cl- is released and taken up during the L(N)-O1 transition from a transiently formed cytoplasmic (CP) binding site and the O2-NM-R3′ or the NM-R3′-original NM-R3 transitions from the extracellular (EC) side, respectively. We propose a mechanism for the Cl- transport by NM-R3 based on our results and its recently reported crystal structure. (Chemical Equation Presented).

Original languageEnglish
Pages (from-to)2027-2038
Number of pages12
JournalJournal of Physical Chemistry B
Issue number9
Publication statusPublished - Mar 9 2017

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry


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