A self-inactivating invertebrate opsin with resistance to retinal depletion optically drives biased signaling toward Gβγ-dependent ion channel modulation

Animal opsins, light-sensitive G protein-coupled receptors (GPCRs), have been utilized for optogenetic tools to control G protein-dependent signaling pathways. Upon G protein activation, the Gα and Gβγ subunits drive different intracellular signaling pathways, leading to complex cellular responses. For some purposes, Gα-, Gβγ- dependent signaling needs to be separately modulated, but these responses are simultaneously evoked due to the 1:1 stoichiometry of Gα and Gβγ. Nevertheless, we show temporal activation of G protein using a self-inactivating invertebrate opsin, Platynereis c-opsin1, drives biased signaling for Gβγ-dependent GIRK channel activation in a light-dependent manner by utilizing the kinetic difference between Gβγ-dependent and Gα-dependent responses. The opsin-induced transient Gi/o activation preferably causes activation of the kinetically-fast Gβγ-dependent GIRK channels rather than slower Gi/oα-dependent adenylyl cyclase inhibition. Although similar Gβγ-biased signaling properties were observed in a self-inactivating vertebrate visual pigment, Platynereis c-opsin1 needs fewer retinal molecules to evoke cellular responses. Furthermore, the Gβγ-biased signaling properties of Platynereis c-opsin1 are enhanced by genetically fused with RGS8 protein which accelerates G protein inactivation. The self-inactivating invertebrate opsin and its RGS8-fusion protein can function as optical control tools biased for Gβγ-dependent ion channel modulation. ### Competing Interest Statement The authors have declared no competing interest.