Juxtamembrane region of the amino terminus of the corticotropin releasing factor receptor type 1 is important for ligand interaction

The functional properties of the amino terminus (NT) of the corticotropin r eleasing factor (CRF) receptor type 1 (R1) were studied by use of murine (m ) CRFR1 and rat (r) parathyroid hormone (PTH)/parathyroid hormone-related p eptide receptor (PTH1R) chimeras. The chimeric receptor CXP, in which the N T of mCRFR1 was annealed to the TMs of PTH1R, and the reciprocal hybrid, PX C, bound radiolabeled analogues of sauvagine and PTH(3-34), respectively. N either hybrid bound radiolabeled CRF or PTH(1-34). CRF and PTH(1-34) weakly stimulated intracellular cAMP accumulation in COS-7 cells transfected with PXC and CXP, respectively. Thus the NT is required for ligand binding and the TMs are required for agonist-stimulated cAMP accumulation. Replacing in dividual intercysteine segments of PXC with their mCRFR1 counterparts did n ot rescue CRF or sauvagine radioligand binding or stimulation of cAMP accum ulation. Replacement of residues 1-31 of mCRFR1 with their PTH1R counterpar ts resulted in a chimeric receptor, PEG, which had normal CRFR1 functional properties. In addition, a series of chimeras (F1PEC-F6PEC) were generated by replacement of the NT intercysteine residues of PEC with their PTH1R cou nterparts. Only F1PEC, F2PEC, and F3PEC showed detectable CRF and sauvagine radioligand binding. All of the PEC chimeras except F5PEC increased cAMP a ccumulation. These data indicate that the Cys(68-)Glu(109) domain is import ant for binding and that the Cys(87)-Cys(102) region plays an important rol e in CRFR1 activation.