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.
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.
Li
Jian Hua
JH
Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea.
Choe
Han
H
Wang
Ai Fen
AF
Maiti
Kaushik
K
Wang
Chengbing
C
Salam
Abdus
A
Chun
Sang Young
SY
Lee
Won-Kyo
WK
Kim
Kyungjin
K
Kwon
Hyuk Bang
HB
Seong
Jae Young
JY
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
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)-