Selmi-Ruby S, Casanova J, Malhotra S, Roussett B, Raaka B M, Samuels H H
Division of Molecular Endocrinology, Department of Medicine, New York University Medical Center, NY 10016, USA.
Mol Cell Endocrinol. 1998 Mar 16;138(1-2):105-14. doi: 10.1016/s0303-7207(98)00016-1.
The ligand binding domain (LBD) of thyroid hormone (T3) receptors contains subdomains that participate in transcriptional activation, hormone-relieved repression and dimerization. A sequence conserved within the nuclear receptor superfamily is found at positions 397-405 of the 408-amino acid chicken T3 receptor-alpha (cTR alpha) and is deleted in the related avian v-erbA. Since v-erbA exhibits compromised ligand binding and transcriptional activation, this conserved region may play a role in ligand-dependent transcriptional activation. Transfections reveal that cTR alpha(1-392) and site-directed mutants cTR alpha(L398R) and cTR alpha(F399E) are inactive, while cTR alpha(1-403) displays reduced ligand-dependent transcriptional activity. The loss of transcriptional activity in cTR alpha(1-392) is not caused by impaired DNA binding or receptor dimer formation. Proteolytic protection assays reveal that both transcriptionally active and inactive cTR alpha derivatives undergo T3-mediated conformational changes. Gal4 chimeras containing the final 16, 35 or 44 amino acids of cTR alpha indicate that the conserved C-terminal region does not function as an independent transactivation domain. Our results are consistent with a model in which ligand plays a structural role to position the conserved C-terminal regions of cTR alpha and related receptors in a transcriptionally active conformation.
甲状腺激素（T3）受体的配体结合结构域（LBD）包含参与转录激活、激素解除抑制和二聚化的亚结构域。在408个氨基酸的鸡T3受体α（cTRα）的397 - 405位发现了核受体超家族中保守的序列，而在相关的禽v-erbA中该序列缺失。由于v-erbA表现出受损的配体结合和转录激活，这个保守区域可能在配体依赖性转录激活中起作用。转染实验表明，cTRα（1 - 392）以及定点突变体cTRα（L398R）和cTRα（F399E）无活性，而cTRα（1 - 403）表现出降低的配体依赖性转录活性。cTRα（1 - 392）转录活性的丧失不是由DNA结合受损或受体二聚体形成受损引起的。蛋白水解保护试验表明，转录活性和无活性的cTRα衍生物都经历T3介导的构象变化。含有cTRα最后16、35或44个氨基酸的Gal4嵌合体表明，保守的C末端区域不作为独立的转录激活结构域发挥作用。我们的结果与一个模型一致，即配体起结构作用，将cTRα和相关受体的保守C末端区域定位在转录活性构象中。
