Chazenbalk G D, Nagayama Y, Russo D, Wadsworth H L, Rapoport B
Thyroid Molecular Biology Unit, Veterans Administration Medical Center, San Francisco, California.
J Biol Chem. 1990 Dec 5;265(34):20970-5.
The thyrotropin (TSH) receptor belongs to a family of guanine nucleotide protein-coupled receptors with seven transmembrane-spanning regions joined regulatory together by extracellular and intracellular loops. The cytoplasmic domain comprises three cytoplasmic loops and a cytoplasmic tail that are likely to be important in coupling of the receptor to the guanine nucleotide proteins. To address the question of which portions of the cytoplasmic domain of the TSH receptor are important in this process, we have altered groups of amino acids in the region of the TSH receptor by site-directed mutagenesis. Because of the low affinity of TSH binding to the TSH receptor mutated in the amino terminus of the second cytoplasmic loop and the amino terminus of the cytoplasmic tail, definitive conclusions cannot be made regarding the roles of these regions in signal transduction. However, our data indicate that the first cytoplasmic loop (residues 441-450), the carboxyl-terminal region of the second cytoplasmic loop (residues 528-537), and the carboxyl-terminal (but not the amino-terminal) region of the third cytoplasmic loop (residues 617-625) are important in the ability of the TSH receptor to mediate an increase in intracellular cAMP production. Furthermore, two-thirds of the carboxyl-terminal end of the cytoplasmic tail (residues 709-764; corresponding to the region not conserved between the TSH and lutropin/chorionic gonadotropin receptors) can be removed without functional impairment of the TSH receptor.
促甲状腺激素（TSH）受体属于鸟嘌呤核苷酸蛋白偶联受体家族，具有七个跨膜区，通过细胞外和细胞内环连接在一起进行调节。细胞质结构域包括三个细胞质环和一个细胞质尾巴，它们可能在受体与鸟嘌呤核苷酸蛋白的偶联中起重要作用。为了解决TSH受体细胞质结构域的哪些部分在此过程中很重要的问题，我们通过定点诱变改变了TSH受体区域中的氨基酸组。由于TSH与在第二个细胞质环的氨基末端和细胞质尾巴的氨基末端发生突变的TSH受体结合的亲和力较低，因此无法就这些区域在信号转导中的作用得出明确结论。然而，我们的数据表明，第一个细胞质环（第441 - 450位氨基酸残基）、第二个细胞质环的羧基末端区域（第528 - 537位氨基酸残基）以及第三个细胞质环的羧基末端（而非氨基末端）区域（第617 - 625位氨基酸残基）在TSH受体介导细胞内cAMP产生增加的能力中很重要。此外，细胞质尾巴羧基末端的三分之二（第709 - 764位氨基酸残基；对应于TSH与促黄体生成素/绒毛膜促性腺激素受体之间不保守的区域）可以去除而不会损害TSH受体的功能。
