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J. Biol. Chem., Vol. 283, Issue 20, 13913-13922, May 16, 2008

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Characterization of the Arabidopsis Heterotrimeric G Protein^*

Shiyu Wang, Sarah M. Assmann, and Nina V. Fedoroff^¶1

From the Department of Biology, Huck Institutes of the Life Sciences, Penn State University, University Park, Pennsylvania 16802 and ^¶Santa Fe Institute, Santa Fe, New Mexico 87501

We have used fluorescence resonance energy transfer and co-immunoprecipitation to analyze the interactions among the , β, and 1 subunits of the Arabidopsis heterotrimeric G protein. Using cyan and yellow fluorescent protein fusion constructs, we show that overexpressed G₁ localizes to protoplast membranes, but Gβ exhibits membrane localization only when the G₁ protein is co-overexpressed. Overexpressed G shows membrane localization unaccompanied by overexpression of either Gβ or G₁. We detect fluorescence resonance energy transfer between Gβ and G₁ in the absence of G overexpression and between G and G₁ but only when all three subunits are co-overexpressed. Both G and Gβ are associated with large macromolecular complexes of 700 kDa in the plasma membrane. G is present in both large complexes and as free G in plasma membranes from wild type plants. In plants homozygous for a null allele of the Gβ gene, G is associated with smaller complexes in the 200–400-kDa range, indicating that its presence in the large complex depends on association with Gβ. Activation of the G subunit with guanosine 5'-3-O-(thio)triphosphate (GTPS) results in partial dissociation of G from the complex. Hydrogen peroxide (H₂O₂) promotes extensive dissociation of the G complex but does not interfere with binding of GTPS to purified recombinant G, suggesting that reactive oxygen species affect the stability of the large complex but not the activity of G itself.

Received for publication, February 20, 2008

^* This work was supported by United States Department of Agriculture Grant 2002-35100-12139 and National Science Foundation (NSF) Grant MCB-0447506 (to N. V. F.) with additional support from NSF Grant MCB-0209694 (to S. M. A.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: 219 Wartik Laboratory, PA State University, University Park, PA 16802. Fax: 814-8636699; E-mail: nvf1{at}psu.edu.