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 (CRF1), 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 CRF1 by a peptide (alpha-helical CRF(9-41)) and non-peptide antagonist (antalarmin), to determine whether the conformational requirements of the activated CRF1 states for Gs and Gi coupling are similar or different. Experimental approach: We studied the inhibitory effect of alpha-helical CRF(9-41) and antalarmin on the coupling of CRF1 to Gs- and Gi-protein in human embryonic kidney cells, using the [S-35]-GTP gamma 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 CRF1 activation by assuming that CRF1 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 CRF1.