Color-Discriminating Retinal Configurations of Sensory RhodopsinI by Photo-Irradiation Solid-State NMR Spectroscopy

SRI (sensory rhodopsinI) can discriminate multiple colors for the attractant and repellent phototaxis. Studies aimed at revealing the color-dependent mechanism show that SRI is a challenging system not only in photobiology but also in photochemistry. During the photoreaction of SRI, an M-intermediate (attractant) transforms into a P-intermediate (repellent) by absorbing blue light. Consequently, SRI then cycles back to the G-state. The photoreactions were monitored with the 13CNMR signals of [20-13C]retnal-SrSRI using insitu photo-irradiation solid-state NMR spectroscopy. The M-intermediate was trapped at -40°C by illumination at 520nm. It was transformed into the P-intermediate by subsequent illumination at 365nm. These results reveal that the G-state could be directly transformed to the P-intermediate by illumination at 365nm. Thus, the stationary trapped M- and P-intermediates are responsible for positive and negative phototaxis, respectively.