Fig. 1.

Activity of CaRhGC in Xenopus oocytes. a Model of the dimeric rhodopsin-guanylyl cyclases from Catenaria anguillulae (Ca). The photo-sensitive rhodopsin domain (yellow) is directly connected to the guanylyl cyclase domain (blue) via a coiled-coil stretch (red). b Single plane confocal images of a non-injected oocyte (top left) and an oocyte expressing the first 1–425 aa (CaRh) inserted between the two halves of a split YFP (top right, bottom left, bottom right: *region magnified, scale bar = 500 µm). YFP fluorescence is reconstituted in oocytes 3 days after injection. c Representative currents from a Xenopus oocyte, expressing CaRhGC together with the cGMP-sensitive CNGA2 channel in response to green light (blue traces, light 2 s, 560 ± 60 nm, intensities as depicted). No photocurrents were detected in oocytes expressing CaRhGC alone or together with a cAMP-sensitive CNGA2 channel (gray traces, 2 s, 560 ± 60 nm, 0.28 mW mm⁻²). d Half saturation of current initial slopes (EC₅₀), deduced from c was reached at 0.027 mW mm⁻², the light intensity-response relationship was fitted exponentially. e, f ELISA-based quantification of cGMP (e) and cAMP (f) from whole oocyte lysates. Oocytes expressing untagged CaRhGC, YFP-tagged CaRhGC (N- or C-terminal) were kept in darkness or illuminated with green light (1 min, 532 nm 0.3 mW mm⁻²). Data are presented as mean ± s.d., n = 3 samples of 5 oocytes each, ***p = 0.0002, **p = 0.002, *p = 0.02, unpaired t-tests light vs dark. ^###p = 0.0001, Dunnett’s multiple comparisons vs control (dark conditions, following one-way ANOVA (p < 0.0001)). Control = non-injected oocytes, CNG = channel cyclic nucleotide-gated channel