A structural model of the constitutive androstane receptor defines novel interactions that mediate ligand-independent activity
A structural model of the constitutive androstane receptor defines novel interactions that mediate ligand-independent activity
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DOI：
10.1128/mcb.22.15.5270-5280.2002
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发表时间：
2002-08-01
影响因子：
5.3
通讯作者：
Forman, BM
中科院分区：
文献类型：
--
作者：
Dussault, I;Lin, M;Forman, BM
与需要配体进行转录活性的经典核受体不同，组成型雄甾烷受体（CAR）在没有配体的情况下也具有活性。为了确定这种构成活性背后的分子接触，我们创建了 CAR 的三维模型，并通过突变分析验证了关键的结构特征。我们发现，在经典受体中促进配体依赖性活性的相同基序也在 CAR 中介导组成型活性。这就提出了一个关键问题：这些基序如何在未配体的 CAR 中保持活性构象？该模型确定了几种解释此活动的新颖交互作用。首先，CAR 在螺旋 11 和反式激活结构域（螺旋 12）之间拥有一个短环，以及一个短的羧基末端螺旋。总之，这些特征有利于反式激活结构域在配体激活受体特征位置上的配体独立对接。其次，这种活性构象通过电荷-电荷相互作用进一步稳定，该相互作用将羧基末端激活结构域锚定到螺旋4。这些相互作用的突变分析为该模型提供了直接的实验支持。我们还表明，配体介导的组成性活性抑制反映了共激活子的置换和辅阻遏物的募集。我们的数据表明，CAR 利用与最初为经典核受体定义的相同的保守结构基序和共调节蛋白。尽管存在这些显着的相似之处，我们的模型证明了 CAR 中的一些关键变化如何能够显着逆转该蛋白质的转录活性。
Unlike classical nuclear receptors that require ligand for transcriptional activity, the constitutive androstane receptor (CAR) is active in the absence of ligand. To determine the molecular contacts that underlie this constitutive activity, we created a three-dimensional model of CAR and verified critical structural features by mutational analysis. We found that the same motifs that facilitate ligand-dependent activity in classical receptors also mediated constitutive activity in CAR. This raises a critical question: how are these motifs maintained in an active conformation in unliganded CAR? The model identified several novel interactions that account for this activity. First, CAR possesses a short loop between helix 11 and the transactivation domain (helix 12), as well as a short carboxy-terminal helix. Together, these features favor ligand-independent docking of the transactivation domain in a position that is characteristic of ligand-activated receptors. Second, this active conformation is further stabilized by a charge-charge interaction that anchors the carboxy-terminal activation domain to helix 4. Mutational analysis of these interactions provides direct experimental support for this model. We also show that ligand-mediated repression of constitutive activity reflects both a displacement of coactivator and a recruitment of corepressor. Our data demonstrate that CAR utilizes the same conserved structural motifs and coregulator proteins as originally defined for classical nuclear receptors. Despite these remarkable similarities, our model demonstrates how a few critical changes in CAR can dramatically reverse the transcriptional activity of this protein.