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Sci. Signal., 28 September 2010
Vol. 3, Issue 141, p. ra71
[DOI: 10.1126/scisignal.2000980]

RESEARCH ARTICLES

Coupling Mechanism of a GPCR and a Heterotrimeric G Protein During Chemoattractant Gradient Sensing in Dictyostelium

Xuehua Xu1*, Tobias Meckel1*{dagger}, Joseph A. Brzostowski2, Jianshe Yan1, Martin Meier-Schellersheim3, and Tian Jin1{ddagger}

1 Chemotaxis Signal Section, National Institutes of Health, Rockville, MD 20852, USA.
2 Laboratory of Immunogenetics Imaging Facility, Laboratory of Immunogenetics, National Institutes of Health, Rockville, MD 20852, USA.
3 Program in Systems Immunology and Infectious Disease Modeling, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.

* These authors contributed equally to this work.

{dagger} Present address: Department of Biology, Technische Universität Darmstadt, Schnittspahnstrasse 3-5, D-64287 Darmstadt, Germany.

Abstract: The coupling of heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (GPCRs) with G proteins is fundamental for GPCR signaling; however, the mechanism of coupling is still debated. Moreover, how the proposed mechanisms affect the dynamics of downstream signaling remains unclear. Here, through experiments involving fluorescence recovery after photobleaching and single-molecule imaging, we directly measured the mobilities of cyclic adenosine monophosphate (cAMP) receptor 1 (cAR1), a chemoattractant receptor, and a G protein β{gamma} subunit in live cells. We found that cAR1 diffused more slowly in the plasma membrane than did Gβ{gamma}. Upon binding of ligand to the receptor, the mobility of cAR1 was unchanged, whereas the speed of a fraction of the faster-moving Gβ{gamma} subunits decreased. Our measurements showed that cAR1 was relatively immobile and Gβ{gamma} diffused freely, suggesting that chemoattractant-bound cAR1 transiently interacted with G proteins. Using models of possible coupling mechanisms, we computed the temporal kinetics of G protein activation. Our fluorescence resonance energy transfer imaging data showed that fully activated cAR1 induced the sustained dissociation of G protein {alpha} and β{gamma} subunits, which indicated that ligand-bound cAR1 activated G proteins continuously. Finally, simulations indicated that a high-affinity coupling of ligand-bound receptors and G proteins was essential for cAR1 to translate extracellular gradient signals into directional cellular responses. We suggest that chemoattractant receptors use a ligand-induced coupling rather than a precoupled mechanism to control the activation of G proteins during chemotaxis.

{ddagger} To whom correspondence should be addressed. E-mail: tjin{at}niaid.nih.gov

Citation: X. Xu, T. Meckel, J. A. Brzostowski, J. Yan, M. Meier-Schellersheim, T. Jin, Coupling Mechanism of a GPCR and a Heterotrimeric G Protein During Chemoattractant Gradient Sensing in Dictyostelium. Sci. Signal. 3, ra71 (2010).

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