The bacterium Geotalea uraniireducens, commonly found in uranium-contaminated environments, plays a key role in bioremediation strategies by converting the soluble hexavalent form of uranium (UVI) into less soluble forms (e.g. UIV.). While most of the reduction and concomitant precipitation of uranium occur outside the cells, there have been reports of important reduction processes taking place in the periplasm. In any case, the triheme periplasmic cytochromes are crucial players, either by ensuring an effective interface between the cell´s interior and exterior or by directly participating in the reduction of the metal. Therefore, understanding the functional mechanism of the highly abundant G. uraniireducens' triheme cytochromes is crucial to assist the elucidation on the respiratory pathways in this bacterium. In this work, a detailed functional characterization of the triheme cytochromes PpcA and PpcB from G. uraniireducens was conducted using NMR and visible spectroscopy techniques. Despite sharing high amino acid sequence and structural homology with their counterparts from G. sulfurreducens, the results obtained showed that the heme reduction potential values are less negative, the order of oxidation of the hemes is distinct, and the redox and redox-Bohr network of interactions revealed unprecedented functional mechanisms of the G. uraniireducens cytochromes. In these cytochromes, the reduction potential values of the three heme groups are much more similar, hence covering a narrow range of values, features that facilitate the directional electron flow from the inner membrane, thereby favouring the optimal reduction of uranium.

中文翻译：

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通过 G. uraniireducens 细菌的细胞色素对铀生物修复的新见解。


Geotalea uraniireducens 细菌常见于铀污染环境中，通过将可溶性六价形式的铀 （UVI） 转化为难溶形式（例如 UIV.），在生物修复策略中起着关键作用。虽然铀的大部分还原和伴随沉淀发生在细胞外，但有报道称重要的还原过程发生在周质中。无论如何，三血红素周质细胞色素都是关键角色，要么确保细胞内部和外部之间的有效界面，要么直接参与金属的还原。因此，了解高丰度的 G. uraniireducens 的三血红素细胞色素的功能机制对于帮助阐明该细菌的呼吸途径至关重要。在这项工作中，使用 NMR 和可见光谱技术对 G. uraniireducens 的三血红素细胞色素 PpcA 和 PpcB 进行了详细的功能表征。尽管与来自硫还原球菌的对应物共享高氨基酸序列和结构同源性，但获得的结果表明，血红素还原电位值不那么负值，血红素的氧化顺序不同，并且氧化还原和氧化还原-玻尔相互作用网络揭示了尿酸杆菌细胞色素前所未有的功能机制。在这些细胞色素中，三个血红素基团的还原电位值更加相似，因此涵盖了一个狭窄的值范围，这些特征促进了从内膜定向流出，从而有利于铀的最佳还原。