title: Noncatalytic domains of RGS9-1.Gbeta 5L play a decisive role in establishing its substrate specificity.
abstract: The complex between the photoreceptor-specific regulator of G protein signaling (RGS) protein, RGS9-1, and type 5 G protein beta-subunit, Gbeta5L, regulates the duration of the cellular response to light by stimulating the GTPase activity of G protein, transducin. An important property of RGS9-1.Gbeta5L is that it interacts specifically with transducin bound to its effector, cGMP phosphodiesterase, rather than with transducin alone. The minimal structure within the RGS9-1.Gbeta5L complex capable of activating transducin GTPase is the catalytic domain of RGS9. This domain itself is also able to discriminate between free and effector-bound transducin but to a lesser degree than RGS9-1.Gbeta5L. The goal of this study was to determine whether other, noncatalytic domains of RGS9-1.Gbeta5L enhance the intrinsic specificity of the catalytic domain or whether they set the specificity of RGS9-1.Gbeta5L regardless of the specificity of its catalytic domain. We found that a double L353E/R360P amino acid substitution reversed the specificity of the recombinant catalytic domain but did not reverse the specificity of RGS9-1.Gbeta5L. However, the degree of discrimination between free and effector-bound transducin was reduced. Therefore, noncatalytic domains of RGS9-1.Gbeta5L play a decisive role in establishing its substrate specificity, yet the high degree of this specificity observed under physiological conditions requires an additional contribution from the catalytic domain.
authors.affiliation: Department of Ophthalmology, Harvard Medical School and the Massachusetts Eye and Ear Infirmary, Boston Massachusetts 02114, USA.
authors.forename: Kirill A
authors.initials: KA
authors.lastname: Martemyanov
authors.forename: Vadim Y
authors.initials: VY
authors.lastname: Arshavsky
mesh_terms: D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D006152:Cyclic GMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020710:RGS Proteins / Q000737:chemistry*; D012160:Retina / Q000378:metabolism; D013379:Substrate Specificity; D015293:Transducin / Q000737:chemistry* / Q000378:metabolism
chemical_list: D020710:RGS Proteins; C116925:regulator of g-protein signaling 9; D020558:GTP Phosphohydrolases; D015293:Transducin; D006152:Cyclic GMP