The Study and Application of Photoreceptive Membrane Protein, Rhodopsin

Microbial rhodopsins are photoreceptive seven-transmembrane proteins diversely found in unicellular microorganisms. The chromophore of microbial rhodopsin is all-trans retinal. The retinal isomerizes to 13-cis form upon light-absorption and it triggers the expression of various biological functions by light. We studied the mechanism of various types of microbial rhodopsins (H+ pump, Cl− pump and sensors) by physicochemical spectroscopic methods. On the basis of these studies, we found the importance of the residues on the third helix (helix C) for the function of microbial rhodopsin, and it led to the discovery of a new functional class of microbial rhodopsin, light-driven outward Na+ pump. The mechanism of Na+ pump rhodopsin was studied by several spectroscopic methods and X-ray crystallography. These studies provided new insights very informative for the development of novel functional artificial rhodopsins (K+ and Cs+ pumps). These new natural and artificial rhodopsins are expected to have high potential for applications such as optogenetics.