G Protein Selectivity Is a Determinant of RGS2 Function*
- Scott P. Heximer‡§,
- Sreesha P. Srinivasaद,
- Leah S. Bernstein‡,
- Jennifer L. Bernard‡,
- Maurine E. Linder‡,
- John R. Hepler‖ and
- Kendall J. Blumer‡**
- From the ‡Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110 and the ‖Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322
Abstract
RGS (regulator of Gprotein signaling) proteins are GTPase-activating proteins that attenuate signaling by heterotrimeric G proteins. Whether the biological functions of RGS proteins are governed by quantitative differences in GTPase-activating protein activity toward various classes of Gα subunits and how G protein selectivity is achieved by differences in RGS protein structure are largely unknown. Here we provide evidence indicating that the function of RGS2 is determined in part by differences in potency toward Gq versus Gi family members. RGS2 was 5-fold more potent than RGS4 as an inhibitor of Gq-stimulated phosphoinositide hydrolysis in vivo. In contrast, RGS4 was 8-fold more potent than RGS2 as an inhibitor of Gi-mediated signaling. RGS2 mutants were identified that display increased potency toward Gi family members without affecting potency toward Gq. These mutations and the structure of RGS4-Giα1 complexes suggest that RGS2-Giα interaction is unfavorable in part because of the geometry of the switch I binding pocket of RGS2 and a potential interaction between the α8-α9 loop of RGS2 and αA of Gi class α subunits. The results suggest that the function of RGS2 relative to other RGS family members is governed in part by quantitative differences in activity toward different classes of Gα subunits.
Footnotes
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↵* This work was supported by National Institutes of Heath Grants GM44592 (to K. J. B.), GM51466 (to M. E. L.), and NS37112 (to J. R. H.) and funds from the American Heart Association (to K. J. B.), Monsanto (to K. J. B. and M. E. L.), American Heart Association-Georgia Affiliate (to J. R. H.), and the Pharmaceuticals Research and Manufacturers of America Foundation (to J. R. H.).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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↵§ These authors contributed equally to this work.
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↵¶ Present address: Div. of Discovery Oncology, Monsanto Company, St. Louis, MO 63198.
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↵** Established Investigator of the American Heart Association. To whom correspondence should be addressed: Dept. of Cell Biology and Physiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110. Tel.: 314-362-1668; Fax: 314-362-7463; E-mail address: kblumer@cellbio.wustl.edu.
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↵2 S. P. Heximer and K. J. Blumer, unpublished results.
- Abbreviations:
- G protein
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guanine nucleotide-binding regulatory protein
- GAP
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GTPase-activating protein
- GFP
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green fluorescent protein
- IP3
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inositol 1,4,5-trisphosphate
- PLC
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phospholipase C
- GTPγS
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guanosine 5′-3-O-(thio)triphosphate
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- Received May 11, 1999.
- Revision received August 26, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
