A Mollusk Retinoic Acid Receptor (RAR) Ortholog Sheds Light on the Evolution of Ligand Binding
A Mollusk Retinoic Acid Receptor (RAR) Ortholog Sheds Light on the Evolution of Ligand Binding
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DOI：
10.1210/en.2014-1181
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发表时间：
2014-11-01
期刊：
影响因子：
4.8
通讯作者：
Laudet, Vincent
中科院分区：
文献类型：
--
作者：
Gutierrez-Mazariegos, Juliana;Nadendla, Eswar Kumar;Laudet, Vincent
核受体是调节靶基因网络以响应小分子的转录因子。我们对这些受体的认识存在很大的偏差，因为它们主要存在于经典模式生物中，主要是脊椎动物。因此，特定的配体-受体对的进化起源仍然难以捉摸。在这里，我们提出了一个视黄酸受体（RAR）的鉴定和表征的软体动物Nucella lapillus（NlRAR）。我们发现，这种受体特异性结合到DNA反应元件组织在直接重复作为异源二聚体与维甲酸X受体。令人惊讶的是，我们还发现NlRAR不结合全反式维甲酸或我们测试的任何其他类维生素A。此外，NlRAR不能响应于类维生素A的刺激而激活报告基因的转录，并且在这些化合物的存在下不能募集共激活因子。NlRAR的配体结合结构域的三维建模揭示了与脊椎动物RAR相似的整体结构。然而，在软体动物受体的配体结合口袋（LBP）中，与配体相互作用的几个残基的改变显然导致了与配体相互作用强度的总体下降。因此，在LBP内的关键位置处的NlRAR的突变产生响应于类视色素的受体。总之，我们的数据表明，在软体动物中，RAR已经失去了其亲和力的全反式视黄酸，突出了其LBP的进化可塑性。当放在进化的背景下，我们的研究结果揭示了核受体的新的结构和功能特征，这些特征经过数百万年的进化验证，在模式生物中是不可能揭示的。
Nuclear receptors are transcription factors that regulate networks of target genes in response to small molecules. There is a strong bias in our knowledge of these receptors because they were mainly characterized in classical model organisms, mostly vertebrates. Therefore, the evolutionary origins of specific ligand-receptor couples still remain elusive. Here we present the identification and characterization of a retinoic acid receptor (RAR) from the mollusk Nucella lapillus (NlRAR). We show that this receptor specifically binds to DNA response elements organized in direct repeats as a heterodimer with retinoid X receptor. Surprisingly, we also find that NlRAR does not bind all-trans retinoic acid or any other retinoid we tested. Furthermore, NlRAR is unable to activate the transcription of reporter genes in response to stimulation by retinoids and to recruit coactivators in the presence of these compounds. Three-dimensional modeling of the ligand-binding domain of NlRAR reveals an overall structure that is similar to vertebrate RARs. However, in the ligand-binding pocket (LBP) of the mollusk receptor, the alteration of several residues interacting with the ligand has apparently led to an overall decrease in the strength of the interaction with the ligand. Accordingly, mutations of NlRAR at key positions within the LBP generate receptors that are responsive to retinoids. Altogether our data suggest that, in mollusks, RAR has lost its affinity for all-trans retinoic acid, highlighting the evolutionary plasticity of its LBP. When put in an evolutionary context, our results reveal new structural and functional features of nuclear receptors validated by millions of years of evolution that were impossible to reveal in model organisms.