Purpose
UNC119 is a protein partner of transducin-α (Gαt) shown to be important for transducin trafficking in rods. We have examined the solution structure of the UNC119/ Gαt complex by SAXS in order to gain insights into the mechanism of transducin trafficking.
Methods
UNC119 and myristoylated chimeric Gαt were co-expressed in E. coli. A highly pure UNC119/ Gαt complex with excellent monodispersity was obtained by a three-step chromatographic procedure. SAXS data on the UNC119/ Gαt complex were collected using different exposure times of synchrotron radiation and varying concentrations of the complex. Combined rigid-body/ab initio modeling against the SAXS data was performed using known atomic structures of UNC119 and Gαt.
Results
Analyses of the scattering curves for the protein complex indicated a radius of gyration (Rg) of 34.7 Å and a maximum particle dimension (Dmax) of 117 Å. The model of the UNC119/ Gαt complex with the best fit to the SAXS data indicated rotation and bending of the N-terminal α-helix (αN) of Gαt from its position in the structure of heterotrimeric Gt. This conformation of αN allows a considerably more compact overall conformation of the complex in which the two molecules have additional interactions involving the β3-β4 loop and the α5-helix/C-terminus of Gαt.
Conclusions
The SAXS solution structure of the UNC119/ Gαt complex suggests a novel interface between UNC119 and Gαt. This interface is potentially critical to the ability of UNC119 to solubilize transducin from the membrane and facilitate its trafficking.
Keywords: 648 photoreceptors •
659 protein structure/function •
714 signal transduction