Nagayama Y, Wadsworth H L, Chazenbalk G D, Russo D, Seto P, Rapoport B
Thyroid Molecular Biology Unit, Veterans Administration Medical Center, San Francisco, CA 94121.
Proc Natl Acad Sci U S A. 1991 Feb 1;88(3):902-5. doi: 10.1073/pnas.88.3.902.
To define the sites in the extracellular domain of the human thyrotropin (TSH) receptor that are involved in TSH binding and signal transduction we constructed chimeric thyrotropin-luteinizing hormone/chorionic gonadotropin (TSH-LH/CG) receptors. The extracellular domain of the human TSH receptor was divided into five regions that were replaced, either singly or in various combinations, with homologous regions of the rat LH/CG receptor. The chimeric receptors were stably expressed in Chinese hamster ovary cells. The data obtained suggest that the carboxyl region of the extracellular domain (amino acid residues 261-418) and particularly the middle region (residues 171-260) play a role in signal transduction. The possibility is also raised of an interaction between the amino and carboxyl regions of the extracellular domain in the process of signal transduction. With respect to hormone binding, substitution of the entire extracellular domain of the LH/CG receptor for the corresponding region of the TSH receptor resulted in high-affinity human CG binding with complete loss of TSH binding. Surprisingly, however, there was at least one chimera with a substitution at each of the five domains that still retained high-affinity TSH binding. Substitution of residues 1-170 of the TSH receptor with the corresponding region of the LH/CG receptor was associated with the retention of high-affinity TSH binding but ligand specificity was lost in that TSH and human CG could interact functionally with the receptor. In summary, these studies suggest that the middle region and carboxyl half of the extracellular domain of the TSH receptor are involved in signal transduction and that the TSH-binding region is likely to span the entire extracellular domain, with multiple discontinuous contact sites.
为了确定人促甲状腺激素（TSH）受体细胞外结构域中参与TSH结合和信号转导的位点，我们构建了嵌合促甲状腺激素-促黄体生成素/绒毛膜促性腺激素（TSH-LH/CG）受体。人TSH受体的细胞外结构域被分为五个区域，这些区域被大鼠LH/CG受体的同源区域单独或多种组合替换。嵌合受体在中国仓鼠卵巢细胞中稳定表达。获得的数据表明，细胞外结构域的羧基区域（氨基酸残基261-418），特别是中间区域（残基171-260）在信号转导中起作用。在信号转导过程中，细胞外结构域的氨基和羧基区域之间也存在相互作用的可能性。关于激素结合，用LH/CG受体的整个细胞外结构域替换TSH受体的相应区域导致高亲和力人CG结合，同时TSH结合完全丧失。然而，令人惊讶的是，至少有一个在五个结构域中的每一个都有替换的嵌合体仍然保留高亲和力TSH结合。用LH/CG受体的相应区域替换TSH受体的残基1-170与保留高亲和力TSH结合相关，但配体特异性丧失，因为TSH和人CG可以与该受体发生功能性相互作用。总之，这些研究表明，TSH受体细胞外结构域的中间区域和羧基半部分参与信号转导，并且TSH结合区域可能跨越整个细胞外结构域，具有多个不连续的接触位点。
