RHODOPSIN CONTROLS A CONFORMATIONAL SWITCH ON THE TRANSDUCIN gamma SUBUNIT
Kisselev, O.G., Downs, M.A.(2003) Structure 11: 367-373
- PubMed: 12679015 
- DOI: https://doi.org/10.1016/s0969-2126(03)00045-5
- Primary Citation of Related Structures:  
1MF6 - PubMed Abstract: 
Rhodopsin, a prototypical G protein-coupled receptor, catalyzes the activation of a heterotrimeric G protein, transducin, to initiate a visual signaling cascade in photoreceptor cells. The betagamma subunit complex, especially the C-terminal domain of the transducin gamma subunit, Gtgamma(60-71)farnesyl, plays a pivotal role in allosteric regulation of nucleotide exchange on the transducin alpha subunit by light-activated rhodopsin. We report that this domain is unstructured in the presence of an inactive receptor but forms an amphipathic helix upon rhodopsin activation. A K65E/E66K charge reversal mutant of the gamma subunit has diminished interactions with the receptor and fails to adopt the helical conformation. The identification of this conformational switch provides a mechanism for active GPCR utilization of the betagamma complex in signal transfer to G proteins.
Organizational Affiliation: 
Department of Ophthalmology, Saint Louis University School of Medicine, St. Louis, MO 63104, USA. kisselev@slu.edu