How GPCRs and G proteins interact is important for their biologic functions and their functions as pharmacologic targets. It is still an open question whether receptors and G proteins are preassembled in a complex or interact only after receptor activation. We compared the propensity of the two Gs-coupled serotonin (5-HT) receptors 5-HT4 and 5-HT7 to associate with G protein prior to agonist activation. Combining receptor-immobilized fluorescence recovery after photobleaching and fluorescence resonance energy transfer methodologies, we observed that 5-HT7 receptors markedly reduced the diffusion of both Gα and Gβγ at the cell surface, which indicated 5-HT7 receptor preassociation with Gs. This is in sharp contrast to the 5-HT4 receptor for which the diffusion of Gαβγ was not modified, and agonist activation brought together the receptor and Gγ, which is consistent with interaction by collision coupling. Agonist activation of 5-HT7 dissociated Gγ from the receptor, whereas Gαs underwent a rapid conformational change with respect to both Gγ and the receptor, followed by a slower dissociation of Gγ from both Gαs and the receptor. Taken together, these data demonstrate a different propensity among receptors to preassociate with G protein in the absence of ligand and reveals a rapid conformational change in Gαs upon activation by the receptor.-Andressen, K. W., Ulsund, A. H., Krobert, K. A., Lohse, M. J., Bünemann, M., Levy, F. O. Related GPCRs couple differently to Gs: preassociation between G protein and 5-HT7 serotonin receptor reveals movement of Gαs upon receptor activation.
Keywords: FRAP; FRET; Gnas; collision coupling; precoupling.