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 (α-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.
We studied the inhibitory effect of α-helical CRF(9–41) and antalarmin on the coupling of CRF1 to Gs- and Gi-protein in human embryonic kidney cells, using the [35S]-GTPγS binding stimulation assay.
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.
British Journal of Pharmacology (2006) 149, 942–947. doi:10.1038/sj.bjp.0706926