Ferritin-like proteins, Dps (DNA-binding protein from starved cells), store iron and play a key role in the iron homeostasis in bacteria, yet their iron releasing machinery remains largely unexplored. The electron donor proteins that may interact with Dps and promote the mobilization of the stored iron have hitherto not been identified. Here, we investigate the binding capacity of the two atypical Dps proteins NpDps4 and NpDps5 from Nostoc punctiforme to isolated ferredoxins. We report NpDps-ferredoxin interactions by fluorescence correlation spectroscopy (FCS) and fluorescence resonance energy transfer (FRET) methods. Dynamic light scattering, size exclusion chromatography and native gel electrophoresis results show that NpDps4 forms a dodecamer at both pH 6.0 and pH 8.0, while NpDps5 forms a dodecamer only at pH 6.0. In addition, FCS data clearly reveal that the non-canonical NpDps5 interacts with DNA at pH 6.0. Our spectroscopic analysis shows that [FeS] centers of the three recombinantly expressed and isolated ferredoxins are properly incorporated and are consistent with their respective native states. The results support our hypothesis that ferredoxins could be involved in cellular iron homeostasis by interacting with Dps and assisting the release of stored iron.

中文翻译：

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来自蓝藻点状细菌的两个非典型Dps的结构扩散特性揭示了与铁氧还蛋白和DNA的相互作用。

铁蛋白样蛋白Dps（饥饿细胞中的DNA结合蛋白）可存储铁并在细菌的铁稳态中发挥关键作用，但它们的铁释放机制仍未开发。迄今为止，尚未发现可能与Dps相互作用并促进所存储的铁的动员的电子供体蛋白。在这里，我们调查点状鼻菜的两个非典型Dps蛋白NpDps4和NpDps5与分离的铁氧还蛋白的结合能力。我们通过荧光相关光谱法（FCS）和荧光共振能量转移（FRET）方法报告了NpDps-铁氧还蛋白相互作用。动态光散射，尺寸排阻色谱和天然凝胶电泳结果表明，NpDps4在pH 6.0和pH 8.0时均形成十二聚体，而NpDps5仅在pH 6.0时形成十二聚体。此外，FCS数据清楚地表明，非经典NpDps5与pH 6.0的DNA相互作用。我们的光谱分析表明，三种重组表达和分离的铁氧还蛋白的[FeS]中心已正确掺入并与它们各自的天然状态一致。结果支持我们的假设，即铁氧还蛋白可以通过与Dps相互作用并协助释放所存储的铁而参与细胞铁稳态。