Evidence that corticotropin‐releasing factor receptor type 1 couples to Gs‐ and Gi‐proteins through different conformations of its J‐domain

Background and purpose: According to the two‐domain model for the corticotropin‐releasing factor receptor type 1 (CRF 1 ), peptide antagonists bind to the N‐terminal domain (N‐domain), non‐peptide antagonists to the transmembrane region (J‐domain), whereas peptide agonists attach to both the N‐ and J‐domain of the receptor to express activity. The aim of this study was to search for possible differences in the antagonism of the Gs‐ and Gi‐protein coupling of CRF 1 by a peptide ( α ‐helical CRF(9–41)) and non‐peptide antagonist (antalarmin), to determine whether the conformational requirements of the activated CRF 1 states for Gs and Gi coupling are similar or different. Experimental approach: We studied the inhibitory effect of α ‐helical CRF(9–41) and antalarmin on the coupling of CRF 1 to Gs‐ and Gi‐protein in human embryonic kidney cells, using the [ 35 S]‐GTP γ S binding stimulation assay. Key results: The non‐peptide antagonized the receptor coupling to Gs competitively but that to Gi noncompetitively, and its antagonistic potency was different for urocortin‐ and sauvagine‐evoked G‐protein activation. In contrast, the peptide antagonist exhibited uniformly competitive antagonism. Conclusions and Implications: The results allow us to extend the two‐domain model of CRF 1 activation by assuming that CRF 1 agonists activate the receptor by binding to at least two ensembles of J‐domain configurations which couple to Gs or Gi, that are in turn antagonized by a non‐peptide antagonist competitively and allosterically, respectively. It is further concluded that the allosteric mechanism of non‐peptide antagonism is not valid for the Gs‐mediated physiological activities of CRF 1 . British Journal of Pharmacology (2006) 149 , 942–947. doi: 10.1038/sj.bjp.0706926