1bh2: Difference between revisions

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A326S MUTANT OF AN INHIBITORY ALPHA SUBUNIT

OverviewOverview

Agonist-bound heptahelical receptors activate heterotrimeric G proteins by catalyzing exchange of GDP for GTP on their alpha subunits. In search of an approximation of the receptor-alpha subunit complex, we have considered the properties of A326S Gialpha1, a mutation discovered originally in Gsalpha (Iiri, T., Herzmark, P., Nakamoto, J. M., Van Dop, C., and Bourne, H. R. (1994) Nature 371, 164-168) that mimics the effect of receptor on nucleotide exchange. The mutation accelerates dissociation of GDP from the alphai1beta1gamma2 heterotrimer by 250-fold. Nevertheless, affinity of mutant Gialpha1 for GTPgammaS is high in the presence of Mg2+, and the mutation has no effect on the intrinsic GTPase activity of the alpha subunit. The mutation also uncouples two activities of betagamma: stabilization of the GDP-bound alpha subunit (which is retained) and retardation of GDP dissociation from the heterotrimer (which is lost). For wild-type and mutant Gialpha1, beta gamma prevents irreversible inactivation of the alpha subunit at 30 degreesC. However, the mutation accelerates irreversible inactivation of alpha at 37 degreesC despite the presence of beta gamma. Structurally, the mutation weakens affinity for GTPgammaS by steric crowding: a 2-fold increase in the number of close contacts between the protein and the purine ring of the nucleotide. By contrast, we observe no differences in structure at the GDP binding site between wild-type heterotrimers and those containing A326S Gialpha1. However, the GDP binding site is only partially occupied in crystals of G protein heterotrimers containing A326S Gialpha1. In contrast to original speculations about the structural correlates of receptor-catalyzed nucleotide exchange, rapid dissociation of GDP can be observed in the absence of substantial structural alteration of a Galpha subunit in the GDP-bound state.

About this StructureAbout this Structure

1BH2 is a Single protein structure of sequence from Rattus norvegicus with and as ligands. Full crystallographic information is available from OCA.

ReferenceReference

The A326S mutant of Gialpha1 as an approximation of the receptor-bound state., Posner BA, Mixon MB, Wall MA, Sprang SR, Gilman AG, J Biol Chem. 1998 Aug 21;273(34):21752-8. PMID:9705312

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-[[Image:1bh2.jpg|left|200px]]<br /><applet load="1bh2" size="450" color="white" frame="true" align="right" spinBox="true"
+[[Image:1bh2.jpg|left|200px]]<br /><applet load="1bh2" size="350" color="white" frame="true" align="right" spinBox="true"
 caption="1bh2, resolution 2.1&Aring;" />
 '''A326S MUTANT OF AN INHIBITORY ALPHA SUBUNIT'''<br />
 ==Overview==
-Agonist-bound heptahelical receptors activate heterotrimeric G proteins by, catalyzing exchange of GDP for GTP on their alpha subunits. In search of, an approximation of the receptor-alpha subunit complex, we have considered, the properties of A326S Gialpha1, a mutation discovered originally in, Gsalpha (Iiri, T., Herzmark, P., Nakamoto, J. M., Van Dop, C., and Bourne, H. R. (1994) Nature 371, 164-168) that mimics the effect of receptor on, nucleotide exchange. The mutation accelerates dissociation of GDP from the, alphai1beta1gamma2 heterotrimer by 250-fold. Nevertheless, affinity of, mutant Gialpha1 for GTPgammaS is high in the presence of Mg2+, and the, mutation has no effect on the intrinsic GTPase activity of the alpha, subunit. The mutation also uncouples two activities of betagamma:, stabilization of the GDP-bound alpha subunit (which is retained) and, retardation of GDP dissociation from the heterotrimer (which is lost). For, wild-type and mutant Gialpha1, beta gamma prevents irreversible, inactivation of the alpha subunit at 30 degreesC. However, the mutation, accelerates irreversible inactivation of alpha at 37 degreesC despite the, presence of beta gamma. Structurally, the mutation weakens affinity for, GTPgammaS by steric crowding: a 2-fold increase in the number of close, contacts between the protein and the purine ring of the nucleotide. By, contrast, we observe no differences in structure at the GDP binding site, between wild-type heterotrimers and those containing A326S Gialpha1., However, the GDP binding site is only partially occupied in crystals of G, protein heterotrimers containing A326S Gialpha1. In contrast to original, speculations about the structural correlates of receptor-catalyzed, nucleotide exchange, rapid dissociation of GDP can be observed in the, absence of substantial structural alteration of a Galpha subunit in the, GDP-bound state.
+Agonist-bound heptahelical receptors activate heterotrimeric G proteins by catalyzing exchange of GDP for GTP on their alpha subunits. In search of an approximation of the receptor-alpha subunit complex, we have considered the properties of A326S Gialpha1, a mutation discovered originally in Gsalpha (Iiri, T., Herzmark, P., Nakamoto, J. M., Van Dop, C., and Bourne, H. R. (1994) Nature 371, 164-168) that mimics the effect of receptor on nucleotide exchange. The mutation accelerates dissociation of GDP from the alphai1beta1gamma2 heterotrimer by 250-fold. Nevertheless, affinity of mutant Gialpha1 for GTPgammaS is high in the presence of Mg2+, and the mutation has no effect on the intrinsic GTPase activity of the alpha subunit. The mutation also uncouples two activities of betagamma: stabilization of the GDP-bound alpha subunit (which is retained) and retardation of GDP dissociation from the heterotrimer (which is lost). For wild-type and mutant Gialpha1, beta gamma prevents irreversible inactivation of the alpha subunit at 30 degreesC. However, the mutation accelerates irreversible inactivation of alpha at 37 degreesC despite the presence of beta gamma. Structurally, the mutation weakens affinity for GTPgammaS by steric crowding: a 2-fold increase in the number of close contacts between the protein and the purine ring of the nucleotide. By contrast, we observe no differences in structure at the GDP binding site between wild-type heterotrimers and those containing A326S Gialpha1. However, the GDP binding site is only partially occupied in crystals of G protein heterotrimers containing A326S Gialpha1. In contrast to original speculations about the structural correlates of receptor-catalyzed nucleotide exchange, rapid dissociation of GDP can be observed in the absence of substantial structural alteration of a Galpha subunit in the GDP-bound state.
 ==About this Structure==
-BH2 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Rattus_norvegicus Rattus norvegicus] with MG and GSP as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1BH2 OCA].
+BH2 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Rattus_norvegicus Rattus norvegicus] with <scene name='pdbligand=MG:'>MG</scene> and <scene name='pdbligand=GSP:'>GSP</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1BH2 OCA].
 ==Reference==
@@ Line 13: / Line 13: @@
 [[Category: Rattus norvegicus]]
 [[Category: Single protein]]
-[[Category: Gilman, A.G.]]
+[[Category: Gilman, A G.]]
-[[Category: Mixon, M.B.]]
+[[Category: Mixon, M B.]]
-[[Category: Posner, B.A.]]
+[[Category: Posner, B A.]]
-[[Category: Sprang, S.R.]]
+[[Category: Sprang, S R.]]
-[[Category: Wall, M.A.]]
+[[Category: Wall, M A.]]
 [[Category: GSP]]
 [[Category: MG]]
 [[Category: signal transduction protein]]
-''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Tue Nov 20 11:39:13 2007''
+''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 11:55:14 2008''