Fig. 3: Light activation of rho in ROS disc membrane signalling through G_t to release Gα_t•GDP to effect hydrolysis of cGMP and its release from PDE6.

a, Native mass spectra of G_t•GDP with no additional GTP added containing two α-isoforms (α₁ and α₂) and two γ-isoforms (γ₁ and γ₂) are catalysed to apo-G_t during a 15-s time course of illumination. b, Reaction scheme: rho* catalysed the nucleotide exchange of G_t. c, The ratio of ground-state G_t•GDP to intermediate apo-G_t decreases rapidly during the first 15 s after illumination. Data are presented as mean ± s.e. (n = 3). d, Native mass spectra of PDE6 ejected from ROS disc membrane vesicles under dark conditions reveal that cGMP binds to intact tetrameric PDE6 with an approximately 1:1 ratio (top). A low population of PDE6–Gα_t•GTP is also observed (red circles). After exposure to light in the presence of ROS disc membranes, the population of PDE6 bound to cGMP is reduced considerably, consistent with the release of GMP following its hydrolysis via activated PDE6 with addition of a molar equivalent of GTPγS to G_t (bottom). e, Schematic shows the rho* signalling cascade that involves the conjugation of all-trans-retinal with PE and its light activation to form cis-retinal that is able to interact with opsin. Light-activated conversion of rho to an intermediate state takes place with rho* capable of interacting with G_t. Changes in the lipid bilayer are depicted as unsaturated lipids that are recruited during rho* signalling (lipids, orange). The Gα_t•GTP subunit produced following hydrolysis of Gα_t•GDP interacts with PDE6, relieving its inhibition via the γ-subunit and effecting the hydrolysis of cGMP, which is then released from PDE6. Gα_t•GDP is formed for the regeneration of G_t•GDP. All experiments shown in this figure were repeated at least three times. Data are presented as mean ± s.e. (n = 3).