Spectroscopic characteristics of: Rubricoccus marinus xenorhodopsin (Rm XeR) and a putative model for its inward H+ transport mechanism

Saki Inoue, Susumu Yoshizawa, Yu Nakajima, Keiichi Kojima, Takashi Tsukamoto, Takashi Kikukawa, Yuki Sudo

Research output: Contribution to journalArticle

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Abstract

A new group of microbial rhodopsins named xenorhodopsins (XeR), which are closely related to the cyanobacterial Anabaena sensory rhodopsin, show a light-driven "inward" proton transport activity, as reported for one representative of this group from Parvularcula oceani (PoXeR). In this study, we functionally and spectroscopically characterized a new member of the XeR clade from a marine bacterium Rubricoccus marinus SG-29T (RmXeR). Escherichia coli cells expressing recombinant RmXeR showed a light-induced alkalization of the cell suspension, which was strongly impaired by a protonophore, suggesting that RmXeR is a light-driven "inward" proton pump as is PoXeR. The spectroscopic properties of purified RmXeR were investigated and compared with those of PoXeR and a light-driven "outward" proton pump, bacteriorhodopsin (BR) from the archaeon Halobacterium salinarum. Action spectroscopy revealed that RmXeR with all-trans retinal is responsible for the light-driven inward proton transport activity, but not with 13-cis retinal. From pH titration experiments and mutational analysis, we estimated the pKa values for the protonated Schiff base of the retinal chromophore and its counterion as 11.1 ± 0.07 and 2.1 ± 0.07, respectively. Of note, the direction of both the retinal composition change upon light-dark adaptation and the acid-induced spectral shift was opposite that of BR, which is presumably related to the opposite directions of ion transport (from outside to inside for RmXeR and from inside to outside for BR). Flash photolysis experiments revealed the appearances of three intermediates (L, M and O) during the photocycle. The proton uptake and release were coincident with the formation and decay of the M intermediate, respectively. Together with associated findings from other microbial rhodopsins, we propose a putative model for the inward proton transport mechanism of RmXeR.

Original languageEnglish
Pages (from-to)3172-3183
Number of pages12
JournalPhysical Chemistry Chemical Physics
Volume20
Issue number5
DOIs
Publication statusPublished - Feb 7 2018

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Bacteriorhodopsins
protons
Protons
Microbial Rhodopsins
Proton Pumps
dark adaptation
light adaptation
Sensory Rhodopsins
anabaena
pumps
Schiff Bases
Photolysis
Chromophores
Escherichia
Titration
titration
Escherichia coli
bacteria
imines
chromophores

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Spectroscopic characteristics of : Rubricoccus marinus xenorhodopsin (Rm XeR) and a putative model for its inward H+ transport mechanism. / Inoue, Saki; Yoshizawa, Susumu; Nakajima, Yu; Kojima, Keiichi; Tsukamoto, Takashi; Kikukawa, Takashi; Sudo, Yuki.

In: Physical Chemistry Chemical Physics, Vol. 20, No. 5, 07.02.2018, p. 3172-3183.

Research output: Contribution to journalArticle

Inoue, Saki ; Yoshizawa, Susumu ; Nakajima, Yu ; Kojima, Keiichi ; Tsukamoto, Takashi ; Kikukawa, Takashi ; Sudo, Yuki. / Spectroscopic characteristics of : Rubricoccus marinus xenorhodopsin (Rm XeR) and a putative model for its inward H+ transport mechanism. In: Physical Chemistry Chemical Physics. 2018 ; Vol. 20, No. 5. pp. 3172-3183.
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