Optogenetic potentials of diverse animal opsins

Abstract

Animal opsin-based pigments are light-activated G-protein-coupled receptors (GPCRs), which drive signal transduction cascades via G proteins. Thousands of animal opsins have been identified, and molecular phylogenetic and biochemical analyses have revealed that opsin-based pigments have basically diversified in selective activation of G proteins (Gs, Gq, Gi, Go, and transducin). Here, we discuss the optogenetic potentials of diverse animal opsins, particularly Gq-coupled spider opsin, Gs-coupled jellyfish opsin, and Gi/Go-coupled mosquito opsin 3 (Opn3). After absorbing light, these purified opsin-based pigments do not release the chromophore retinal, indicating the bleach-resistant nature of their photoproducts. In addition, unlike vertebrate visual opsin-based pigments that have been conventionally used for optogenetic applications, the stable photoproducts of spider opsin- and mosquito Opn3-based pigments revert to their original dark states upon subsequent light absorption, which indicates their photoregeneration ability. Mammalian cultured cells that express spider opsin exhibit light-induced increases in Ca 2+ levels, and jellyfish opsin- and mosquito Opn3-expressing cells exhibit light-dependent increases and decreases in cyclic adenosine monophosphate (cAMP) levels, respectively. These findings indicate that these pigments control different second messengers, Ca 2+ and cAMP, in mammalian cultured cells, suggesting that these bleach-resistant opsins have an optogenetic potential.