Mutation Analysis of Thyroid Hormone Function

甲状腺激素（TH）信号由两种相关的甲状腺受体（TR）转导，所述甲状腺受体（TR）调节基因表达并且是核受体（NR）超家族的成员，所述核受体（NR）超家族还包括类固醇、维生素和脂肪酸以及各种胆固醇和脂肪酸及其代谢物的受体。目前约有20%的药物是与NR结合的配体，强调了NR家族的重要性。TH调节脂肪量、胆固醇、心脏和其他功能;因此，开发选择性调节TR作用的方法可能导致具有选择性作用的有用药物。我们已经利用X射线晶体学信息的TR配体结合（LBD）和DMA结合（DBD）域，以指导TR上的突变的位置，以分析TR的作用机制。这种诱变方法已经使我们能够定义LBD表面结合下游辅助调节因子，介导基因表达的变化，并形成TR-TR二聚体和异源二聚体与类维生素A X受体（RXR）。结果还确定了可能成为新药靶点的位点。在拟议的研究中，我们使用我们的突变库和其他拟议的突变来确定：受体如何区分各种辅阻遏物; TR与辅激活因子（PGC-1）结合的新模式的分子基础; TR和RXR如何适应识别其DMA结合位点的不同方向; TH调节受体与DMA结合的机制;盐桥的作用，影响几个不同的TR功能，在unliganded与配体模式;和一个新的配体如何表现出选择性结合一个特定的TR亚型之间插入一个侧基的配体结合腔外的结构。这些研究应该提供大量的TR功能，这是相关的了解TR的行动，其他NR的行动机制，基因表达的调控和药物设计。

Thyroid hormone (TH) signals are transduced by two related thyroid receptors (TRs) that regulate gene expression and are members of the nuclear receptor (NR) superfamily, which also includes receptors for steroids, vitamins and fatty acids and a variety of cholesterol and fatty acids and their metabolites. About 20% of current Pharmaceuticals are ligands that bind to NRs, underlining the importance of the NR family. TH regulates fat mass, cholesterol, heart and other functions; thus developing means to selectively regulate TR actions could lead to useful Pharmaceuticals with selective actions. We have utilized X-ray crystallographic information about the TR ligand-binding (LBD) and DMA-binding (DBD) domains to guide placements of mutations on the TR to analyze the mechanism of TR action. This mutagenesis approach has already allowed us to define LBD surfaces for binding downstream coregulators that mediate changes in gene expression, arid for forming TR-TR dimers and heterodimers with the retinoid X-receptor (RXR). The results also identified sites that might be targets for novel Pharmaceuticals. In the proposed studies we use our large bank of mutations and additional proposed mutations to determine: how receptors discriminate between various corepressors; the molecular basis of a novel mode of binding of TR to a coactivator (PGC-1); how the TR and RXR adapt to recognize diverse orientations of their DMA binding sites; mechanisms whereby TH regulates receptor binding to DMA; the role of salt bridges that influence several different TR functions in the unliganded vs. the liganded modes; and how a novel ligand exhibits selectivity for binding a particular TR isoform by inserting a side group between structures outside the ligand-binding cavity. These studies should provide substantial insight into TR function that is relevant for understanding TR action, mechanism of action of other NRs, regulation of gene expression and pharmaceutical design.