IscR of Rhodobacter sphaeroides functions as repressor of genes for iron-sulphur metabolism and represents a new type of iron-sulphur binding protein. Cereibacter sphaeroides 2.4.1

Iron-sulphur (Fe-S) clusters are ensembles of iron and sulphide centres. They are found in all life forms and are important components of many enzymes involved in diverse cellular processes, including respiration, DNA synthesis or gene regulation. However, the increase in oxygen after the emergence of oxygenic photosynthesis created a threat to Fe–S proteins and, consequently, to the organisms relying on them. Therefore, bacteria have evolved mechanisms to maintain a precise intracellular iron concentration. A major role of IscR in R. sphaeroides iron dependent regulation was suggested in a bioinformatic study , which predicted a binding site in the upstream regions of several iron uptake genes. Most known IscR proteins have Fe-S clusters featuring (Cys)3(His)1 ligation. However, IscR proteins from Rhodobacteraceae harbour only one Cys residue and it was considered unlikely that they can ligate an Fe-S cluster. In this study, the role of R. sphaeroides IscR as transcriptional regulator and sensor of the Fe-S cluster status of the cell was analysed. The results provide evidence that R. sphaeroides IscR functions as transcriptional repressor of genes involved in iron metabolism by binding to the predicted DNA binding motif. Furthermore, IscR possesses a unique Fe-S cluster ligation scheme with only a single cysteine involved. Overall design: RNA samples collected from a control strain (wild type 2.4.1) and of the iscR deletion strain (2.4.1∆iscR) were analyzed by two-color microarrays

铁硫（Fe-S）簇是由铁与硫化中心组成的复合体，广泛存在于所有生命形式中，是参与呼吸作用、DNA合成及基因调控等多种细胞过程的诸多酶的关键组成部分。然而，产氧光合作用出现后氧气浓度的升高，对Fe-S蛋白乃至依赖此类蛋白的生物体构成了威胁。因此，细菌演化出了维持细胞内铁浓度精准稳态的机制。一项生物信息学研究提示，IscR在球形红杆菌（R. sphaeroides）的铁依赖调控过程中发挥重要作用，该研究预测在多个铁摄取基因的上游区域存在其结合位点。绝大多数已报道的IscR蛋白，其Fe-S簇采用(Cys)3(His)1的配位方式。然而，红杆菌科来源的IscR蛋白仅含有一个半胱氨酸残基，此前认为此类蛋白无法完成Fe-S簇的配位结合。本研究针对球形红杆菌IscR作为转录调控因子以及细胞Fe-S簇状态传感器的功能展开了分析。研究结果证实，球形红杆菌IscR通过结合预测得到的DNA结合基序，充当铁代谢相关基因的转录阻遏因子。此外，该IscR蛋白拥有独特的Fe-S簇配位模式，仅依靠单个半胱氨酸参与配位。实验整体设计：本研究通过双色微阵列技术，对对照菌株（野生型2.4.1）与iscR基因缺失菌株（2.4.1ΔiscR）的RNA样本进行了转录组分析。