IscU, the central scaffold protein in the bacterial ISC iron–sulfur (Fe–S) cluster biosynthesis system, has long been recognized to bind a Zn²⁺ ion at its active site. While initially regarded as an artifact, Zn²⁺ binding has been shown to induce stabilization of the IscU structure that may mimic a state biologically relevant to IscU’s role in Fe–S cluster biosynthesis. More recent studies have revealed that SufU, a homologous protein involved in Fe–S cluster biosynthesis in Gram-positive bacteria, also binds a Zn²⁺ ion with structural implications. Given the widespread occurrence of the “IscU-like” protein fold, particularly among Fe–S cluster biosynthesis systems, an interesting question arises as to whether Zn²⁺ ion binding and the resulting structural alterations are common properties in IscU-like proteins. Interactions between IscU and specific metal ions are investigated and compared side-by-side with those of SufU from a representative Gram-positive bacterium in the phylum Firmicutes. These studies were extended with additional transition metal ions chosen to investigate the influence of coordination geometry on selectivity for binding at the active sites of IscU and SufU. Monitoring and comparing the conformational behavior and stabilization afforded by different transition metal ions upon IscU and SufU revealed similarities between the two proteins and suggest that metal-dependent conformational transitions may be characteristic of U-type proteins involved in Fe–S cluster biosynthesis.

中文翻译：

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细菌IscU和SufU对Zn ²⁺和选择的过渡金属离子响应的比较

IscU是细菌ISC铁-硫（Fe-S）簇生物合成系统中的中心支架蛋白，长期以来人们一直认为它会在其活性位点结合Zn ²⁺离子。尽管最初被认为是人工产物，但已证明Zn ²⁺结合可诱导IscU结构的稳定化，这可能模拟了与IscU在Fe–S团簇生物合成中的作用有关的生物学状态。最近的研究表明，SufU是一种与革兰氏阳性细菌中Fe–S簇生物合成有关的同源蛋白，它也与Zn ²⁺离子结合，具有结构意义。考虑到“ IscU样”蛋白折叠的普遍存在，特别是在Fe–S团簇生物合成系统中，关于Zn ²⁺是否存在一个有趣的问题离子结合和产生的结构改变是IscU样蛋白的共同特性。研究了IscU和特定金属离子之间的相互作用，并将其与Firmicutes门上具有代表性的革兰氏阳性细菌的SufU进行了比较。这些研究通过选择其他过渡金属离子进行扩展，以研究配位几何形状对IscU和SufU活性位点结合选择性的影响。监测和比较不同过渡金属离子对IscU和SufU提供的构象行为和稳定性，揭示了两种蛋白质之间的相似性，并表明金属依赖性构象转变可能是参与Fe–S团簇生物合成的U型蛋白质的特征。