EXTRACELLULAR CYSTEINES OF THE CORTICOTROPIN-RELEASING FACTOR-RECEPTOR ARE CRITICAL FOR LIGAND INTERACTION

The corticotropin-releasing factor receptor (CRF-R) contains six conse rved cysteines in its amino-terminal domain (C30, C44, C54, C68, C87, and C102) and one cysteine in its first and second extracellular loops (C188 and C258, respectively). Additionally, several other cysteines are located in the transmembrane domains (C128, C211, C233, and C364) and first intracellular loop (C150). Reduction of disulfide bonds with DTT decreased CRF binding to detergent-solubilized membranes, suggest ing an important role for disulfide bonds in ligand recognition. There fore, site-directed mutagenesis was used to introduce single and paire d Cys (C) to Ser (S) or Ala (A) mutations. A silent nine amino acid ta g from c myc was introduced in the amino terminus of the mouse CRF-R. With the exception of C258S and C188S/C258S mutations, all C to S or t o A receptor mutants had good surface expression that was at least 52. 5% of control. C30S, C54S, and C30S/C54S mutations had good CRF bindin g and CRF-stimulated cAMP accumulation. No CRF binding was detected fo r the C44S, C68S, C87S, C102S, C188S, C258S, C30S/C44S, C30S/C68S, C54 S/C68S, C87S/C102S, and C188S/C258S mutants, while CRF-stimulated cAMP accumulation occurred with high EC50 values. In particular, receptors carrying double mutations, C44S/C102S and C68S/C87%, had an improved signaling property as compared to receptors carrying the respective si ngle cysteine mutations. These data, together with the effects of DTT on CRF binding, indicate that disulfide bridges are important for rece ptor functions. Functional data from single and paired cysteine mutati ons suggest potential pairings between C44 and C102, C68 and C87, and C188 and C258 that are critical for ligand-receptor interactions.