Pardee Keith I, Xu Xiaohui, Reinking Jeff, Schuetz Anja, Dong Aiping, Liu Suya, Zhang Rongguang, Tiefenbach Jens, Lajoie Gilles, Plotnikov Alexander N, Botchkarev Alexey, Krause Henry M, Edwards Aled
Banting and Best Department of Medical Research, The Department of Molecular Genetics, University of Toronto, Toronto, Canada.
PLoS Biol. 2009 Feb 24;7(2):e43. doi: 10.1371/journal.pbio.1000043.
Heme is a ligand for the human nuclear receptors (NR) REV-ERBalpha and REV-ERBbeta, which are transcriptional repressors that play important roles in circadian rhythm, lipid and glucose metabolism, and diseases such as diabetes, atherosclerosis, inflammation, and cancer. Here we show that transcription repression mediated by heme-bound REV-ERBs is reversed by the addition of nitric oxide (NO), and that the heme and NO effects are mediated by the C-terminal ligand-binding domain (LBD). A 1.9 A crystal structure of the REV-ERBbeta LBD, in complex with the oxidized Fe(III) form of heme, shows that heme binds in a prototypical NR ligand-binding pocket, where the heme iron is coordinately bound by histidine 568 and cysteine 384. Under reducing conditions, spectroscopic studies of the heme-REV-ERBbeta complex reveal that the Fe(II) form of the LBD transitions between penta-coordinated and hexa-coordinated structural states, neither of which possess the Cys384 bond observed in the oxidized state. In addition, the Fe(II) LBD is also able to bind either NO or CO, revealing a total of at least six structural states of the protein. The binding of known co-repressors is shown to be highly dependent upon these various liganded states. REV-ERBs are thus highly dynamic receptors that are responsive not only to heme, but also to redox and gas. Taken together, these findings suggest new mechanisms for the systemic coordination of molecular clocks and metabolism. They also raise the possibility for gas-based therapies for the many disorders associated with REV-ERB biological functions.
血红素是人类核受体（NR）REV-ERBα和REV-ERBβ的配体，这两种转录抑制因子在昼夜节律、脂质和葡萄糖代谢以及糖尿病、动脉粥样硬化、炎症和癌症等疾病中发挥着重要作用。在此我们表明，由结合血红素的REV-ERB介导的转录抑制可通过添加一氧化氮（NO）而逆转，并且血红素和NO的作用是由C端配体结合结构域（LBD）介导的。REV-ERBβ LBD与血红素的氧化Fe（III）形式形成的1.9埃晶体结构表明，血红素结合在典型的NR配体结合口袋中，其中血红素铁由组氨酸568和半胱氨酸384配位结合。在还原条件下，对血红素-REV-ERBβ复合物的光谱研究表明，LBD的Fe（II）形式在五配位和六配位结构状态之间转变，这两种状态均不具有在氧化态中观察到的半胱氨酸384键。此外，Fe（II）LBD还能够结合NO或CO，揭示了该蛋白质总共至少六种结构状态。已知共抑制因子的结合显示高度依赖于这些不同的配体状态。因此，REV-ERB是高度动态的受体，不仅对血红素敏感，而且对氧化还原和气体也有反应。综上所述，这些发现为分子时钟和代谢的系统协调提出了新机制。它们还增加了基于气体疗法治疗与REV-ERB生物学功能相关的许多疾病的可能性。
