title: Light-activated rhodopsin induces structural binding motif in G protein alpha subunit.
abstract: A large superfamily of transmembrane receptors control cellular responses to diverse extracellular signals by catalyzing activation of specific types of heterotrimeric GTP-binding proteins. How these receptors recognize and promote nucleotide exchange on G protein alpha subunits to initiate signal amplification is unknown. The three-dimensional structure of the transducin (Gt) alpha subunit C-terminal undecapeptide Gtalpha(340-350) IKENLKDCGLF was determined by transferred nuclear Overhauser effect spectroscopy while it was bound to photoexcited rhodopsin. Light activation of rhodopsin causes a dramatic shift from a disordered conformation of Gtalpha(340-350) to a binding motif with a helical turn followed by an open reverse turn centered at Gly-348, a helix-terminating C capping motif of an alphaL type. Docking of the NMR structure to the GDP-bound x-ray structure of Gt reveals that photoexcited rhodopsin promotes the formation of a continuous helix over residues 325-346 terminated by the C-terminal helical cap with a unique cluster of crucial hydrophobic side chains. A molecular mechanism by which activated receptors can control G proteins through reversible conformational changes at the receptor-G protein interface is demonstrated.
authors.affiliation: Institute for Biomedical Computing, Washington University Medical School, St. Louis, MO 63110, USA.
authors.forename: O G
authors.initials: OG
authors.lastname: Kisselev
authors.forename: J
authors.initials: J
authors.lastname: Kao
authors.forename: J W
authors.initials: JW
authors.lastname: Ponder
authors.forename: Y C
authors.initials: YC
authors.lastname: Fann
authors.forename: N
authors.initials: N
authors.lastname: Gautam
authors.forename: G R
authors.initials: GR
authors.lastname: Marshall
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002151:Calorimetry; D002417:Cattle; D003198:Computer Simulation; D017124:Conserved Sequence; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008027:Light; D046911:Macromolecular Substances; D051379:Mice; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012984:Software; D015293:Transducin / Q000737:chemistry* / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D010446:Peptide Fragments; D012243:Rhodopsin; D019204:GTP-Binding Proteins; D015293:Transducin