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 sequenc es in the mouse gonadotropin-releasing hormone receptor were mutated t o determine which residues were glycosylated and the function of glyco sylation. Photoaffinity labelled Gln(4) and Gln(18) receptor mutants e xhibited lower apparent molecular weight on SDS polyacrylamide gel ele ctrophoresis, while the Gln(102) receptor showed wildtype mobility. Th is indicates that the receptor is glycosylated at Asn(4) and Asn(18) b ut not at Asn(102). Binding affinities of all the mutant receptors wer e normal, indicating that carbohydrate moieties are not involved in li gand binding interactions. However, expression of the Gln(4) and Gln(1 8) receptors were substantially decreased, indicating a role for glyco sylation in receptor expression or stability. All the glycosylation si te mutants were capable of normal signal transduction, as indicated by their ability to stimulate inositol phosphate production.