The GTPase-activating Protein RGS4 Stabilizes the Transition State for Nucleotide Hydrolysis*
- From the Department of Pharmacology, The University of Texas Southwestern Medical Center, Dallas, Texas 75235
- §To whom correspondence should be addressed: Dept. of Pharmacology, The University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75235.
Abstract
RGS proteins constitute a newly appreciated group of negative regulators of G protein signaling. Discovered by genetic screens in yeast, worms, and other organisms, two mammalian RGS proteins, RGS4 and GAIP, act as GTPase-activating proteins for members of the Gi family of G protein α subunits. We have purified recombinant RGS4 to homogeneity and demonstrate that it acts catalytically to stimulate GTP hydrolysis by Gi proteins. Furthermore, RGS4 stabilizes the transition state for GTP hydrolysis, as evidenced by its high affinity for the GDP-AlF4−-bound forms of Goα and Giα and its relatively low affinity for the GTPγS- and GDP-bound forms of these proteins. Consequently, RGS4 is most likely not a downstream effector for activated Gα subunits. All members of the Gi subfamily of proteins tested are substrates for RGS4 (including Gtα and Gzα); the protein has lower affinity for Gqα, and it does not stimulate the GTPase activity of Gsα or G12α.
Footnotes
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↵‡ Member of the Cell Regulation Graduate Program of University of Texas Southwestern Graduate School of Biomedical Sciences. Supported by the Medical Scientist Training Program and Pharmacological Sciences Training Grant GM07062.
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↵* This work was supported by National Institutes of Health Grant GM34497, the Lucille P. Markey Charitable Trust, and the Raymond and Ellen Willie Chair of Molecular Neuropharmacology. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- G proteins
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heterotrimeric guanine nucleotide-binding proteins
- GAP
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GTPase-activating protein
- GTPγS
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guanosine 5′-(3-O-thio)triphosphate
- C12E10
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polyoxyethylene-10-lauryl ether.
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- Received August 28, 1996.
- © 1996 by The American Society for Biochemistry and Molecular Biology, Inc.
