title: The solution structure of the transducin-α-uncoordinated 119 protein complex suggests occlusion of the Gβ₁γ₁-binding sites.
abstract: Uncoordinated 119 protein (UNC119) is a partner of transducin-α subunit (Gαt ) that is essential for transducin trafficking in rod photoreceptors. The interaction is known to involve binding of the acylated N terminus of Gαt 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 Gαt (Gαt *) and UNC119₅₀₋₂₄₀, and examined the solution structure by small angle X-ray scattering and chemical crosslinking. The solution structure of the Gαt -UNC119₅₀₋₂₄₀ complex was derived with rigid body/ab initio modeling against the small angle X-ray scattering data by use of known atomic structures of Gαt and UNC119, and a distance constraint based on the protein crosslinking with p-phenyldimaleimide. The model of the Gαt -UNC119₅₀₋₂₄₀ complex indicates rotation and bending of the N-terminal α-helix of Gαt 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/α3-β5 surface of Gαt . Supporting a novel interface, UNC119 was found to bind full-length Gαt * more strongly than the Gαt N-terminal peptide. Furthermore, UNC119 competed with the effector molecule phosphodiesterase-6 γ-subunit, which is known to bind to the same surface of Gαt . The solution structure of the Gαt -UNC119 complex suggests that the ability of UNC119 to dissociate Gt subunits and release Gαt from the membrane is attributable to disruption and sterical occlusion of the Gβ₁γ₁-binding sites on Gαt .
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Iowa, IA, USA.
authors.forename: Pallavi
authors.initials: P
authors.lastname: Cheguru
authors.forename: Anurima
authors.initials: A
authors.lastname: Majumder
authors.forename: Ravi
authors.initials: R
authors.lastname: Yadav
authors.forename: Kota N
authors.initials: KN
authors.lastname: Gopalakrishna
authors.forename: Lokesh
authors.initials: L
authors.lastname: Gakhar
authors.forename: Nikolai O
authors.initials: NO
authors.lastname: Artemyev
mesh_terms: D001665:Binding Sites; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism; D015293:Transducin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D015293:Transducin
keywords: chemical crosslinking; molecular modeling; photoreceptors; small-angle X-ray scattering; transducin