Microbial Rhodopsins as Multi-functional Photoreactive Membrane Proteins for Optogenetics

In life science research, methods to control biological activities with stimuli such as light, heat, pressure and chemicals have been widely utilized to understand their molecular mechanisms. The knowledge obtained by those methods has built a basis for the development of medicinal products. Among those various stimuli, light has the advantage of a high spatiotemporal resolution that allows for the precise control of biological activities. Photoactive membrane protein rhodopsins from microorganisms (called microbial rhodopsins) absorb visible light and that light absorption triggers the trans–cis photoisomerization of the chromophore retinal, leading to various functions such as ion pumps, ion channels, transcriptional regulators and enzymes. In addition to their biological significance, microbial rhodopsins are widely utilized as fundamental molecular tools for optogenetics, a method to control biological activities by light. In this review, we briefly introduce the molecular basis of representative rhodopsin molecules and their applications for optogenetics. Based on those examples, we discuss the high potential of rhodopsin-based optogenetics tools for basic and clinical research in pharmaceutical sciences.