Genomic Medicine Program, The Methodist Hospital Research Institute, Houston, Texas, USA.
Nat Struct Mol Biol. 2013 Jun;20(6):740-7. doi: 10.1038/nsmb.2568. Epub 2013 May 5.
IscR from Escherichia coli is an unusual metalloregulator in that both apo and iron sulfur (Fe-S)-IscR regulate transcription and exhibit different DNA binding specificities. Here, we report structural and biochemical studies of IscR suggesting that remodeling of the protein-DNA interface upon Fe-S ligation broadens the DNA binding specificity of IscR from binding the type 2 motif only to both type 1 and type 2 motifs. Analysis of an apo-IscR variant with relaxed target-site discrimination identified a key residue in wild-type apo-IscR that, we propose, makes unfavorable interactions with a type 1 motif. Upon Fe-S binding, these interactions are apparently removed, thereby allowing holo-IscR to bind both type 1 and type 2 motifs. These data suggest a unique mechanism of ligand-mediated DNA site recognition, whereby metallocluster ligation relocates a protein-specificity determinant to expand DNA target-site selection, allowing a broader transcriptomic response by holo-IscR.
大肠杆菌中的 IscR 是一种不同寻常的金属调控因子，因为apo 和铁硫（Fe-S）-IscR 都能调节转录，并表现出不同的 DNA 结合特异性。在这里，我们报告了 IscR 的结构和生化研究，表明 Fe-S 键合后蛋白质-DNA 界面的重塑拓宽了 IscR 的 DNA 结合特异性，使其不仅能结合 2 型模体，还能结合 1 型和 2 型模体。对具有宽松靶位点识别的 apo-IscR 变体的分析确定了野生型 apo-IscR 中的一个关键残基，我们提出，该残基与 1 型模体产生不利相互作用。Fe-S 结合后，这些相互作用显然被消除，从而使全酶 IscR 能够结合 1 型和 2 型模体。这些数据表明了一种独特的配体介导的 DNA 位点识别机制，其中金属簇键合将蛋白特异性决定因素重新定位，从而扩大 DNA 靶位点选择，使全酶 IscR 能够产生更广泛的转录组反应。
