Pogenberg Vivian, Guichou Jean-François, Vivat-Hannah Valérie, Kammerer Sabrina, Pérez Efrén, Germain Pierre, de Lera Angel R, Gronemeyer Hinrich, Royer Catherine A, Bourguet William
Centre de Biochimie Structurale, CNRS U5048-INSERM U554-UM1, Faculté de Pharmacie, 15 avenue Charles Flahault, 34093 Montpellier, France.
J Biol Chem. 2005 Jan 14;280(2):1625-33. doi: 10.1074/jbc.M409302200. Epub 2004 Nov 4.
Retinoid receptors (RARs and RXRs) are ligand-activated transcription factors that regulate the transcription of target genes by recruiting coregulator complexes at cognate promoters. To understand the effects of heterodimerization and ligand binding on coactivator recruitment, we solved the crystal structure of the complex between the RARbeta/RXRalpha ligand-binding domain heterodimer, its 9-cis retinoic acid ligand, and an LXXLL-containing peptide (termed NR box 2) derived from the nuclear receptor interaction domain (NID) of the TRAP220 coactivator. In parallel, we measured the binding affinities of the isolated NR box 2 peptide or the full-length NID of the coactivator SRC-1 for retinoid receptors in the presence of various types of ligands. Our correlative analysis of three-dimensional structures and fluorescence data reveals that heterodimerization does not significantly alter the structure of individual subunits or their intrinsic capacity to interact with NR box 2. Similarly, we show that the ability of a protomer to recruit NR box 2 does not vary as a function of the ligand binding status of the partner receptor. In contrast, the strength of the overall association between the heterodimer and the full-length SRC-1 NID is dictated by the combinatorial action of RAR and RXR ligands, the simultaneous presence of the two receptor agonists being required for highest binding affinity. We identified an LXXLL peptide-driven mechanism by which the concerted reorientation of three phenylalanine side chains generates an "aromatic clamp" that locks the RXR activation helix H12 in the transcriptionally active conformation. Finally, we show how variations of helix H11-ligand interactions can alter the communication pathway linking helices H11, H12, and the connecting loop L11-12 to the coactivator-binding site. Together, our results reveal molecular and structural features that impact on the ligand-dependent interaction of the RAR/RXR heterodimer with nuclear receptor coactivators.
类视黄醇受体（RARs和RXRs）是配体激活的转录因子，通过在同源启动子上募集共调节复合物来调控靶基因的转录。为了了解异源二聚化和配体结合对共激活因子募集的影响，我们解析了RARβ/RXRα配体结合域异源二聚体、其9-顺式视黄酸配体以及源自TRAP220共激活因子核受体相互作用域（NID）的含LXXLL基序的肽段（称为NR框2）之间复合物的晶体结构。同时，我们测定了在各种类型配体存在下，分离的NR框2肽段或共激活因子SRC-1的全长NID与类视黄醇受体的结合亲和力。我们对三维结构和荧光数据的相关分析表明，异源二聚化不会显著改变单个亚基的结构或其与NR框2相互作用的内在能力。同样，我们发现单体募集NR框2的能力不会因伙伴受体的配体结合状态而变化。相反，异源二聚体与全长SRC-1 NID之间整体结合的强度由RAR和RXR配体的协同作用决定，两种受体激动剂同时存在时结合亲和力最高。我们确定了一种由LXXLL肽驱动的机制，通过该机制，三个苯丙氨酸侧链的协同重排产生一个“芳香钳”，将RXR激活螺旋H12锁定在转录活性构象。最后，我们展示了螺旋H11-配体相互作用的变化如何改变连接螺旋H11、H12以及连接环L11-12与共激活因子结合位点的通讯途径。总之，我们的结果揭示了影响RAR/RXR异源二聚体与核受体共激活因子配体依赖性相互作用的分子和结构特征。
