Dependence of agonist activation on an aromatic moiety in the DPLIY motif of the gonadotropin-releasing hormone receptor.
In the GnRH receptor, the NPX2-3Y motif that is present in the seventh transmembrane helix of most G protein-coupled receptors is unusual in containing Asp instead of Asn but retains the highly conserved Tyr residue. The importance of this aromatic residue in the DPLIY sequence of the GnRH receptor function was analyzed by replacing Tyr322 with Ala or Phe residues. The Y322A mutant receptor expressed in COS-7 cells had high agonist binding affinity, but its ability to interact with G protein(s) and to activate inositol phosphate production in response to GnRH was abolished. Although functionally inactive, the Y322A mutant receptor was internalized at about 50% of the rate of the wild type receptor in agonist-treated cells. When Tyr322 was replaced with Phe to preserve its aromatic nature, the Y322F mutant receptor displayed normal G protein activation and inositol phosphate responses to GnRH and was internalized in the same manner as the wild type receptor. These findings demonstrate that the aromatic moiety of the Tyr322 component of the DPLIY motif in the GnRH receptor is a critical determinant of agonist-induced receptor activation and signal transduction.
Arora
K K
KK
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Cheng
Z
Z
Catt
K J
KJ
D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000502:physiology; D015870:Gene Expression; D007987:Gonadotropin-Releasing Hormone / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D017385:Sequence Homology; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014162:Transfection; D014443:Tyrosine
D007295:Inositol Phosphates; D001224:Aspartic Acid; D007987:Gonadotropin-Releasing Hormone; D014443:Tyrosine; D019204:GTP-Binding Proteins