Wang Chengbing, Oh Da Young, Maiti Kaushik, Kwon Hyuk Bang, Cheon Jun, Hwang Jong-Ik, Seong Jae Young
Graduate School of Medicine, Korea University, Seoul 136-705, Korea.
Mol Cells. 2008 Feb 29;25(1):91-8.
The Glu/Asp(7.32) residue in extracellular loop 3 of the mammalian type-I gonadotropin-releasing hormone receptor (GnRHR) interacts with Arg(8) of GnRH-I, conferring preferential ligand selectivity for GnRH-I over GnRH-II. Previously, we demonstrated that the residues (Ser and Pro) flanking Glu/Asp(7.32) also play a role in the differential agonist selectivity of mammalian and non-mammalian GnRHRs. In this study, we examined the differential antagonist selectivity of wild type and mutant GnRHRs in which the Ser and Pro residues were changed. Cetrorelix, a GnRH-I antagonist, and Trptorelix-2, a GnRH-II antagonist, exhibited high selectivity for mammalian type-I and non-mammalian GnRHRs, respectively. The inhibitory activities of the antagonists were dependent on agonist concentration and subtype. Rat GnRHR in which the Ser-Glu-Pro (SEP) motif was changed to Pro-Glu-Val (PEV) or Pro-Glu-Ser (PES) had increased sensitivity to Trptorelix-2 but decreased sensitivity to Cetrorelix. Mutant bullfrog GnRHR-1 with the SEP motif had the reverse antagonist selectivity, with reduced sensitivity to Trptorelix-2 but increased sensitivity to Cetrorelix. These findings indicate that the residues flanking Glu(7.32) are important for antagonist as well as agonist selectivity.
哺乳动物I型促性腺激素释放激素受体（GnRHR）胞外环3中的Glu/Asp(7.32)残基与GnRH-I的Arg(8)相互作用，赋予对GnRH-I比对GnRH-II的优先配体选择性。此前，我们证明了Glu/Asp(7.32)两侧的残基（Ser和Pro）在哺乳动物和非哺乳动物GnRHRs的差异激动剂选择性中也起作用。在本研究中，我们研究了Ser和Pro残基发生改变的野生型和突变型GnRHRs的差异拮抗剂选择性。GnRH-I拮抗剂西曲瑞克和GnRH-II拮抗剂曲普瑞林-2分别对哺乳动物I型和非哺乳动物GnRHRs表现出高选择性。拮抗剂的抑制活性取决于激动剂浓度和亚型。将Ser-Glu-Pro（SEP）基序改变为Pro-Glu-Val（PEV）或Pro-Glu-Ser（PES）的大鼠GnRHR对曲普瑞林-2的敏感性增加，但对西曲瑞克的敏感性降低。具有SEP基序的突变型牛蛙GnRHR-1具有相反的拮抗剂选择性，对曲普瑞林-2的敏感性降低，但对西曲瑞克的敏感性增加。这些发现表明，Glu(7.32)两侧的残基对拮抗剂以及激动剂的选择性都很重要。
