| Research Abstract |
We have investigated the mechanism of biomolecular chemical reactions. In particular, our main target was cis-trans isomerization and proton transfer reactions in rhodopsins, such as light-driven proton pump bacteriorhodopsin and visual rhodopsin. In rhodopsins, specific reactions in protein environments convert light into protein structural changes, whose relaxation leads to the functional processes. In this project, we approached such specificity from both dynamical and structural aspects. Following results were obtained.
As the dynamical aspects, we were able to capture the excited-state dynamics of visual rhodopsin and pharaonis phoborhodopsin, acting as light sensors in our vision and bacterial phototaxis, respectively, by means of femtosecond fluorescence spectroscopy. It was revealed that the protein environment facilitates efficient cis-trans photoisomerization of the retinal chromophore.
As the structural aspects, we monitored protein structural changes through inter-atomic vibrations by (Fourier-transform) infrared spectroscopy. In particular, highly optimized experimental set-up allowed to detect the spectral changes in the X-H and X-D stretching frequency regions for the first time. Direct information on the hydrogen-bonding alterations was obtained. The results involved were for bacteriorhodopsin, color visual pigments for green and red lights, and pharaonis phoborhodopsin. These results provide new structural information on the reaction specificity ; on how protein respond to light, and functional processes are driven.
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