Department of Life Science, Graduate School and Faculty of Engineering Science, Akita University, 1-1 Tegata Gakuen Town, Akita 010-8502, Japan.
J Biochem. 2018 Mar 1;163(3):223-232. doi: 10.1093/jb/mvx074.
The AhR, so called the dioxin receptor, is a member of the nuclear receptor superfamily. The ligand-free AhR forms a cytosolic protein complex with the molecular chaperone HSP90, co-chaperone p23, and XAP2 in the cytoplasm. Following ligand binding like 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD), the AhR translocates into the nucleus. Although it has been reported that HSP90 regulates the translocation of the AhR to the nucleus, the precise activation mechanisms of the AhR have not yet been fully understood. AhR consists of the N-terminal bHLH domain containing NLS and NES, the middle PAS domain and the C-terminal transactivation domain. The PAS domain is familiar as a ligand and HSP90 binding domain. In this study, we focused on the bHLH domain that was thought to be a HSP90 binding domain. We investigated the binding properties of bHLH to HSP90. We analyzed the direct interaction of bHLH with HSP90, p23 and XAP2 using purified proteins. We found that not only the PAS domain but also the bHLH domain bound to HSP90. The bHLH domain forms complex with HSP90, p23 and XAP2. We also determined the bHLH binding domain was HSP90 N-domain. The bHLH domain makes a complex with HSP90, p23 and XAP2 via the HSP90 N-domain. Although the NLS is closed in the absence of a ligand, the structure of AhR will be changed in the presence of a ligand, which leads to NLS open, result in the nuclear translocation of AhR.
芳香烃受体（AhR），又称为二噁英受体，是核受体超家族的成员之一。在细胞质中，无配体的 AhR 与分子伴侣 HSP90、共伴侣 p23 和 XAP2 形成胞质蛋白复合物。在与配体结合（如 2,3,7,8-四氯二苯并-p-二噁英（TCDD））后，AhR 易位到细胞核内。尽管已有报道称 HSP90 调节 AhR 向核内的易位，但 AhR 的精确激活机制尚未完全阐明。AhR 由包含 NLS 和 NES 的 N 端 bHLH 结构域、中间 PAS 结构域和 C 端转录激活结构域组成。PAS 结构域作为配体和 HSP90 结合域而广为人知。在本研究中，我们专注于被认为是 HSP90 结合域的 bHLH 结构域。我们研究了 bHLH 与 HSP90 的结合特性。我们使用纯化蛋白分析了 bHLH 与 HSP90、p23 和 XAP2 的直接相互作用。我们发现不仅 PAS 结构域，而且 bHLH 结构域都与 HSP90 结合。bHLH 结构域与 HSP90、p23 和 XAP2 形成复合物。我们还确定了 bHLH 结合域是 HSP90 的 N 结构域。bHLH 结构域通过 HSP90 的 N 结构域与 HSP90、p23 和 XAP2 形成复合物。尽管在没有配体的情况下 NLS 是封闭的，但在存在配体的情况下，AhR 的结构会发生变化，导致 NLS 开放，从而导致 AhR 的核易位。
