Light-induced structural changes during early photo-intermediates of the eubacterial Cl− pump Fulvimarina rhodopsin observed by FTIR difference spectroscopyElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ra19363j

• Main Authors: Koua, Faisal Hammad Mekky, Kandori, Hideki
• Format: Article
• ISSN: 2046-2069
• DOI: 10.1039/c5ra19363j

Fulvimarina pelagi rhodopsin (FR) is a member of inward eubacterial light-activated Cl − translocating rhodopsins (ClR) that were found recently in marine bacteria. Here, we present the first detailed low-temperature FTIR difference spectroscopy analyses assisted with static UV-visible spectroscopy on this novel ClR, monitoring its FR K and FR L-like (FR L′ ) intermediates at 77 and 220 K, respectively. Light-activated FTIR difference spectra in the fingerprint C-C bands (1290-1040 cm −1 ) and the hydrogen-out-of-plane (HOOP) wagging vibrations of the retinal chromophore indicate similar but not identical configurations of the FR K and FR L′ , and that the retinal undergoes all- trans to 13- cis isomerization upon photo-activation similar to other microbial rhodopsins. Further, the analysis of the C&z.dbd;C ethylenic vibrations reveal that FR K and FR L′ states are red-shifted from the unphotolyzed state. Light-induced FTIR difference spectral analyses of the amide I and amide II regions (1700−1560 cm −1 ) of the protein moiety, further suggest that FR undergoes large protein rearrangements during the primary states of photo-activation. In addition, we tentatively assign the bands at 1628 (−)/1618 (+) cm −1 to the C&z.dbd;N stretching vibrations, that is ∼6 (−)/3 (+) cm −1 downshifted from its archaeal counterpart halorhodopsin. This assignment reveals that FR undergoes no changes in the C&z.dbd;N stretch upon FR L′ -formation, suggesting similar hydrogen-bonding and Schiff base environments between FR K and FR L′ . Fulvimarina pelagi rhodopsin (FR) is a member of inward eubacterial light-activated Cl − translocating rhodopsins (ClR) that were found recently in marine bacteria.