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Time-Resolved FTIR Study of Light-Driven Sodium Pump Rhodopsins

Abstract

Light-driven sodium ion pump rhodopsin (NaR) is a new functional class of microbial rhodopsin. A previous flash photolysis study of Krokinobacter eikastus rhodopsin 2 (KR2) revealed the presence of three kinetically distinct intermediates: K, L/M, and O. Previous low-temperature Fourier-transform infrared (FTIR) spectroscopy of KR2 showed that photoisomerization from the all-trans to the 13-cis form is the primary event of the Na+ pumping photocycle, but structural information of the subsequent intermediates is limited. Here, we applied step-scan time-resolved FTIR spectroscopy to KR2 and Nonlabens dokdonensis rhodopsin 2 (NdR2). Both low-temperature static and time-resolved FTIR spectra resolved a K-like intermediate, and the corresponding spectra showed few differences. Strong hydrogen-out-of-plane (HOOP) vibrations, which appeared in the K intermediate, is common among other rhodopsins. It is however unique for NaR that such HOOP bands are persistent in late intermediates, such as L and O intermediates. This observation strongly suggests common chromophore structures for the K, L, and O intermediates. In fact, an isotope-labeled study that used 12, 14-D2 retinal revealed that the chromophore configuration of the O intermediate in NaR is 13-cis. In contrast to the vibrations of the chromophore, those of protein differ among intermediates, and this is related to the sodium-pumping function. The molecular mechanism of the light-driven sodium pump is discussed on the basis of the present time-resolved FTIR results.

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Publication details

The article was received on 24 Apr 2018, accepted on 11 Jun 2018 and first published on 13 Jun 2018


Article type: Paper
DOI: 10.1039/C8CP02599A
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Time-Resolved FTIR Study of Light-Driven Sodium Pump Rhodopsins

    H. Chen, K. Inoue, H. Ono, R. Abe-Yoshizumi, A. Wada and H. Kandori, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP02599A

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