Related GPCRs couple differently to G(s): preassociation between G protein and 5-HT(7) serotonin receptor reveals movement of Gα(s) upon receptor activation


  • K.W. Andressen
  • A.H. Ulsund
  • K.A. Krobert
  • M.J. Lohse
  • M. Buenemann
  • F.O. Levy


  • FASEB Journal


  • FASEB J 32 (2): 1059-1069


  • 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 G(s)-coupled serotonin (5-HT) receptors 5-HT(4) and 5-HT(7) 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-HT(7) receptors markedly reduced the diffusion of both Gα and Gβγ at the cell surface, which indicated 5-HT(7) receptor preassociation with G(s). This is in sharp contrast to the 5-HT(4) 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-HT(7) dissociated Gγ from the receptor, whereas Gα(s) underwent a rapid conformational change with respect to both Gγ and the receptor, followed by a slower dissociation of Gγ from both Gα(s) 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 Gα(s) upon activation by the receptor.