You are currently viewing the editor's summary.
View Full TextLog in to view the full text
AAAS login provides access to Science for AAAS members, and access to other journals in the Science family to users who have purchased individual subscriptions.
Register for free to read this article
As a service to the community, this article is available for free. Existing users log in.
More options
Download and print this article for your personal scholarly, research, and educational use.
Buy a single issue of Science for just $15 USD.
Ligand-Induced Coupling
A long-standing question regarding the activation of heterotrimeric G proteins by G protein–coupled receptors (GPCRs) is whether the association between the GPCR and the G protein is stimulated by the binding of ligand to the receptor, or whether the receptor and G protein are precoupled. Xu et al. addressed this question by measuring the mobilities of fluorescent fusion proteins of cyclic adenosine monophosphate (cAMP) receptor 1 (cAR1), a GPCR for the chemoattractant cAMP, and the Gβ subunit in live Dictyostelium cells. The receptor and G protein moved independently in the plasma membrane and at different speeds. Whereas exposure of cells to cAMP had no effect on the mobility of cAR1, the mobility of a fraction of the faster-moving G proteins was reduced. Together with computer simulations of the effects of various proposed receptor–G protein coupling mechanisms on downstream signaling, these data suggest that the interaction between cAR1 and its G protein does not occur until the receptor is bound to ligand, and provide a means for investigating the G protein–coupling mechanisms of other GPCRs.
