title: G protein subtype specificity of rhodopsin intermediates metarhodopsin Ib and metarhodopsin II.
abstract: Rhodopsin is one of the members of the G protein-coupled receptor family that can catalyze a GDP-GTP exchange reaction on the retinal G protein transducin (Gt) upon photon absorption. There are at least two intermediate states, meta-Ib and meta-II, which exhibit direct interaction with Gt. Meta-Ib binds to GDP-bound Gt, while meta-II forms a complex with Gt having no nucleotide, suggesting that meta-Ib is a state that initially interacts with Gt. Here we investigated whether or not meta-Ib exhibits specific interaction with G protein similar to meta-II, by examining the binding efficiencies of meta-Ib and meta-II to Gialpha and its mutants whose C-terminal 11 amino acids were replaced with those of Goalpha, Gqalpha and Gsalpha. The affinity of meta-Ib to the C-terminal 11 amino acids of Gtalpha was similar to those of Gialpha and its mutant with Goalpha's C-terminal 11 amino acids, whereas meta-II exhibited affinity to the C-terminal 11 amino acids of Gialpha mutant with Goalpha's C-terminal 11 amino acids about half of what was seen for Gtalpha and Gialpha. Both intermediates exhibited no affinity to the Gialpha mutants containing the C-terminal 11 amino acids of Gqalpha and Gsalpha. These results suggested that meta-Ib is the state that exhibits specific interaction with G protein as meta-II does, although meta-Ib exhibits a slightly lenient binding selectivity compared to that of meta-II.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors.forename: Takefumi
authors.initials: T
authors.lastname: Morizumi
authors.forename: Naoki
authors.initials: N
authors.lastname: Kimata
authors.forename: Akihisa
authors.initials: A
authors.lastname: Terakita
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Imamoto
authors.forename: Takahiro
authors.initials: T
authors.lastname: Yamashita
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Shichida
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D051381:Rats; D012243:Rhodopsin / Q000145:classification / Q000378:metabolism*; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D012243:Rhodopsin; D019204:GTP-Binding Proteins