title: Extracellular loop 3 (EL3) and EL3-proximal transmembrane helix 7 of the mammalian type I and type II gonadotropin-releasing hormone (GnRH) receptors determine differential ligand selectivity to GnRH-I and GnRH-II.
abstract: Mammalian type I and II gonadotropin-releasing hormone (GnRH) receptors (GnRHRs) show differential ligand preference for GnRH-I and GnRH-II, respectively. Using a variety of chimeric receptors based on green monkey GnRHR-2 (gmGnRHR-2), a representative type II GnRHR, and rat GnRHR, a representative type I GnRHR, this study elucidated specific domains responsible for this ligand selectivity. A chimeric gmGnRHR-2 with the extracellular loop 3 (EL3) and EL3-proximal transmembrane helix 7 (TMH7) of rat GnRHR showed a great increase in ligand sensitivity to GnRH-I but not to GnRH-II. Point-mutation studies indicate that four amino acids, Leu/Phe(7.38), Leu/Phe(7.43), Ala/Pro(7.46), and Pro/Cys(7.47) in TMH7 are critical for ligand selectivity as well as receptor conformation. Furthermore, a combinatory mutation (Pro(7.31)-Pro(7.32)-Ser(7.33) motif to Ser-Glu-Pro in EL3 and Leu(7.38), Leu(7.43), Ala(7.46), and Pro(7.47) to those of rat GnRHR) in gmGnRH-2 exhibited an approximately 500-fold increased sensitivity to GnRH-I, indicating that these residues are critical for discriminating GnRH-II from GnRH-I. [Trp(7)]GnRH-I and [Trp(8)]GnRH-I but not [His(5)]GnRH-I exhibit a higher potency in activating wild-type gmGnRHR-2 than native GnRH-I, indicating that amino acids at positions 7 and 8 of GnRHs are more important than position 5 for differential recognition by type I and type II GnRHRs. As a whole, these data suggest a molecular coevolution of ligands and their receptors and facilitate the understanding of the molecular interaction between GnRHs and their cognate receptors.
authors.affiliation: Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea.
authors.forename: Jian Hua
authors.initials: JH
authors.lastname: Li
authors.forename: Han
authors.initials: H
authors.lastname: Choe
authors.forename: Ai Fen
authors.initials: AF
authors.lastname: Wang
authors.forename: Kaushik
authors.initials: K
authors.lastname: Maiti
authors.forename: Chengbing
authors.initials: C
authors.lastname: Wang
authors.forename: Abdus
authors.initials: A
authors.lastname: Salam
authors.forename: Sang Young
authors.initials: SY
authors.lastname: Chun
authors.forename: Won-Kyo
authors.initials: WK
authors.lastname: Lee
authors.forename: Kyungjin
authors.initials: K
authors.lastname: Kim
authors.forename: Hyuk Bang
authors.initials: HB
authors.lastname: Kwon
authors.forename: Jae Young
authors.initials: JY
authors.lastname: Seong
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011966:Receptors, LHRH / Q000737:chemistry* / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: C484844:GNRHR protein, human; C427484:GNRHR2 protein, human; D008024:Ligands; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; C047717:LHRH, His(5)-Trp(7)-Tyr(8)-