Molecular Diversity of Photosensitive Protein Opsins and Their High Potential for Optogenetic Applications.

Because G protein coupled receptors (GPCRs) represent the largest family of drug targets in clinical trials, GPCR signaling cascades are closely related to various physiological phenomena, attracting significant attention in pharmaceutical science. Opsins (also known as animal rhodopsins) are photoreceptive proteins containing retinal as a chromophore, which function as GPCRs and underlie the molecular basis of photoreception in animals. Recently, opsins have been progressively applied in an innovative technology called optogenetics to regulate biological activities using light. A wide variety of opsins have been identified in metazoans and characterized at the molecular and physiological levels, providing a foundation for their optogenetic applications. In this review, I briefly introduce the diversity of opsins in terms of their molecular functions, including G protein selectivity and photoreaction properties. This diversity provides a significant advantage for optically manipulating a wide variety of GPCR signaling cascades with high temporal resolution. Additionally, I discuss the rich array of opsin-based optogenetic tools used to control various physiological processes and their potential as therapeutic tools for vision restoration. Based on the introduction, I expect that the optogenetic approach will offer powerful tools to provide valuable insights into the molecular mechanisms of various physiological phenomena and next-generation treatment options for diseases beyond the capacity of traditional drugs.