N-glycosylation of CRF receptor type 1 is important for its ligand-specific interaction

The corticotropin-releasing factor (CRF) receptor type 1 (CRFR1) contains f ive potential N-glycosylation sites: N38, N45, N78, N90, and N98. Cells exp ressing CRFR1 were treated with tunicamycin to block receptor glycosylation . The nonglycosylated receptor did not bind the radioligand and had a decre ased cAMP stimulation potency in response to CRF. To determine which of the polysaccharide chain(s) is/are involved in ligand interaction, the polysac charide chains were deleted using site-directed mutagenesis of the glycosyl ation consensus, N-X-S/T. Two sets of mutations were performed for each gly cosylation site: N to Q and S/T to A, respectively. The single mutants Q38, Q45, Q78, Q90, Q98, A40, A47, A80, A92, and A100 and the double mutants A4 0/A47 and A80/A100 were well expressed, bound CRF, sauvagine (SVG), and uro tensin-I (UTS-I) with a normal affinity, and increased cAMP accumulation wi th a high efficiency. In contrast, the combined mutations A80/A92/A100, A40 /A80/A92/A100, and A40/A47/A80/A92/A100 had low levels of expression, did n ot bind the radioligand, and had a decreased cAMP stimulation. These data i ndicate the requirement for three or more polysaccharide chains for normal CRFR1 function.