Structural basis for the asymmetric binding of coactivator SRC1 to FXR-RXRα and allosteric communication within the complex

In this study, we employed an integrative approach to investigate the interaction between FXR-RXRα-DNA complex and the entire coactivator SRC1-NRID (nuclear receptor interaction domain). We constructed a multi-domain model of FXR-RXRα-DNA, highlighting the interface between FXR-DBD and LBD. Using HDX-MS, XL-MS, and biochemical assays, we revealed the allosteric communications in FXR-RXRα-DNA upon agonist and DNA binding. We then demonstrated that SRC1 binds only to the coactivator binding surface of FXR within the FXR-RXRα heterodimer, with the NR-box2 and NR-box3 of SRC1 as the key binding motifs. Our findings, which provide the first model of SRC1-NRID in complex with FXR-RXRα-DNA, shed light on the molecular mechanism through which the coactivator asymmetrically interacts with nuclear receptors and provide structural basis for further understanding the function of FXR and its implications in diseases.在本研究中，我们采用整合策略探究FXR-RXRα-DNA复合物与完整共激活因子SRC1-NRID（核受体相互作用域，nuclear receptor interaction domain）之间的相互作用。我们构建了FXR-RXRα-DNA的多结构域模型，着重展示了FXR的DNA结合域（DBD）与配体结合域（LBD）之间的界面。通过氢氘交换质谱（HDX-MS）、交联质谱（XL-MS）及生化实验，我们揭示了激动剂与DNA结合后FXR-RXRα-DNA中的变构通讯。随后，我们证实SRC1仅与FXR-RXRα异二聚体中FXR的共激活因子结合表面结合，其中SRC1的NR-box2和NR-box3为关键结合基序。我们的研究结果首次构建了SRC1-NRID与FXR-RXRα-DNA复合物的模型，揭示了共激活因子与核受体不对称相互作用的分子机制，并为深入理解FXR的功能及其在疾病中的意义提供了结构基础。