Fig. 1: JellyOp activates robust ultrafast GIRK currents via Gαs.

a Differential interference contrast and epi-fluorescence micrographs of the same HEK293 cells transfected with a JellyOp-mKate fusion protein demonstrate highly efficient membrane targeting of JellyOp. Scale bar is 20 μm. b cAMP bioluminescent plate reader assay on JellyOp transfected HEK293 cells performed with (red) and without (black) PTX shows a preference for Gαs but significant coupling to Gαi/o (p = 0.02; one-sided t-test; error bands show mean ± SD). c,d JellyOp efficiently activates GIRK channels with a transient (ts) response onset followed by a small slower sag current. Similar GIRK responses were recorded in stable GIRK1/2 expressing HEK-GIRK cells (c) and in endogenously GIRK1/4 expressing HL-1 cells (d). e The transient response component has an ultrafast onset. f The sag current is abolished by pre-treatment with PTX, indicative of being mediated via Gαi/o (error bands show mean ± SD). g The JellyOp triggered GIRK current recover in the dark with kinetics typical for GPRC rhodopsins (error bands show mean ± SD). h The cAMP response of endogenous Gαs-coupled β2-adrenoceptors in HEK293 cells stimulated with isoproterenol (ISO) is significantly smaller in cells transfected with JellyOp (red; no illumination; 1 μM 9-cis-retinal; p = 0.027 at peak; one-sided t-test; error bands show mean ± SD) compared to control cells transfected with YFP (black). The residual ISO-induced rise in cAMP seen in the red trace likely arises from cells not expressing JellyOp (transfection efficacy ~50%). Light stimulation (500 nm) is indicated as green bars and light intensities are given in figure panels (photons/cm²/s). Source data are provided as a Source Data file.