Structure of the visual signaling complex between transducin and phosphodiesterase 6.
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ABSTRACT:
SUBMITTER: Gao Y
PROVIDER: S-EPMC8208777 | biostudies-literature | 2021 Jun
REPOSITORIES: biostudies-literature
Publications
Structure of the visual signaling complex between transducin and phosphodiesterase 6.
Gao Yang Y Eskici Gözde G Ramachandran Sekar S Poitevin Frédéric F Seven Alpay Burak AB Panova Ouliana O Skiniotis Georgios G Cerione Richard A RA
Molecular cell 20210601 11
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Project description:Heterotrimeric G proteins communicate signals from activated G protein-coupled receptors to downstream effector proteins. In the phototransduction pathway responsible for vertebrate vision, the G protein-effector complex is composed of the GTP-bound transducin α subunit (GαT·GTP) and the cyclic GMP (cGMP) phosphodiesterase 6 (PDE6), which stimulates cGMP hydrolysis, leading to hyperpolarization of the photoreceptor cell. Here we report a cryo-electron microscopy (cryoEM) structure of PDE6 complexed to GTP-bound GαT. The structure reveals two GαT·GTP subunits engaging the PDE6 hetero-tetramer at both the PDE6 catalytic core and the PDEγ subunits, driving extensive rearrangements to relieve all inhibitory constraints on enzyme catalysis. Analysis of the conformational ensemble in the cryoEM data highlights the dynamic nature of the contacts between the two GαT·GTP subunits and PDE6 that supports an alternating-site catalytic mechanism.
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Project description:Uncoordinated 119 protein (UNC119) is a partner of transducin-? subunit (G?t ) that is essential for transducin trafficking in rod photoreceptors. The interaction is known to involve binding of the acylated N terminus of G?t to the hydrophobic pocket of UNC119. To gain insights into the mechanism of transducin trafficking, we isolated a highly pure protein complex between myristoylated chimeric G?t (G?t *) and UNC119??????, and examined the solution structure by small angle X-ray scattering and chemical crosslinking. The solution structure of the G?t -UNC119?????? complex was derived with rigid body/ab initio modeling against the small angle X-ray scattering data by use of known atomic structures of G?t and UNC119, and a distance constraint based on the protein crosslinking with p-phenyldimaleimide. The model of the G?t -UNC119?????? complex indicates rotation and bending of the N-terminal ?-helix of G?t from its position in the structure of the heterotrimeric G-protein transducin (Gt ). This allows a considerably more compact complex conformation, which also suggests a novel interface involving the switch II/?3-?5 surface of G?t . Supporting a novel interface, UNC119 was found to bind full-length G?t * more strongly than the G?t N-terminal peptide. Furthermore, UNC119 competed with the effector molecule phosphodiesterase-6 ?-subunit, which is known to bind to the same surface of G?t . The solution structure of the G?t -UNC119 complex suggests that the ability of UNC119 to dissociate Gt subunits and release G?t from the membrane is attributable to disruption and sterical occlusion of the G????-binding sites on G?t .
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