IDENTIFICATION OF N-GLYCOSYLATION SITES IN THE GONADOTROPIN-RELEASING-HORMONE RECEPTOR - ROLE IN RECEPTOR EXPRESSION BUT NOT LIGAND-BINDING

The asparagine residues of the three N-glycosylation consensus sequences in the mouse gonadotropin-releasing hormone receptor were mutated to determine which residues were glycosylated and the function of glycosylation. Photoaffinity labelled Gln(4) and Gln(18) receptor mutants exhibited lower apparent molecular weight on SDS polyacrylamide gel electrophoresis, while the Gln(102) receptor showed wildtype mobility. This indicates that the receptor is glycosylated at Asn(4) and Asn(18) but not at Asn(102). Binding affinities of all the mutant receptors were normal, indicating that carbohydrate moieties are not involved in ligand binding interactions. However, expression of the Gln(4) and Gln(18) receptors were substantially decreased, indicating a role for glycosylation in receptor expression or stability. All the glycosylation site mutants were capable of normal signal transduction, as indicated by their ability to stimulate inositol phosphate production.