Autologous biological response modification of the gonadotropin receptor

It is generally held with respect to heterotrimeric guanine nucleotide bind ing protein-coupled receptors that binding of ligand stabilizes a conformat ion of receptor that activates adenylyl cyclase, It is not formally appreci ated if, in the case of G-protein-coupled receptors with large extracellula r domains (ECDs), ECDs directly participate in the activation process. The large ECD of the glycoprotein hormone receptors (GPHRs) is 350 amino acids in length, composed of seven leucine-rich repeat domains, and necessary and sufficient: for high affinity binding of the glycoprotein hormones. Peptid e challenge experiments to identify regions in the follicle-stimulating hor mone (FSH) receptor (FSHR) ECD that could bind its cognate ligand identifie d only a single synthetic peptide corresponding to residues 221-252, which replicated a leucine-rich repeat domain of the FSHR ECD and which had intri nsic activity. This peptide inhibited human FSH binding to the human FSHR ( hFSHR) and also inhibited human FSH-induced signal transduction in Y-1 cell s expressing recombinant hFSHR. The hFSRR-(221-252) domain was not accessib le to anti-peptide antibody probes, suggesting that this domain resides at an interface between the hFSHR ECD and transmembrane domains. CD spectrosco py of the peptide in dodecyl phosphocholine micelles showed an increase in the ordered structure of the peptide. CD and NMR spectroscopies of the pept ide in trifluoroethanol confirmed that hFSRR-(221-252) has the propensity t o form ordered secondary structure. Importantly and consistent with the for egoing results, dodecyl phosphocholine induced a significant increase in th e ordered secondary structure of the purified hFSHR ECD as well. These data provide biophysical evidence of the influence of environment on GPHR ECD s ubdomain secondary structure and identify a specific activation domain that ; can autologously modify GPHR activity.