Gaudu P, Moon N, Weiss B
Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109-0602, USA.
J Biol Chem. 1997 Feb 21;272(8):5082-6. doi: 10.1074/jbc.272.8.5082.
SoxR protein, a transcriptional activator of the soxRS (superoxide response) regulon of Escherichia coli, contains autooxidizable [2Fe-2S] centers that are presumed to serve as redox sensors. In vitro transcription experiments previously demonstrated that only the oxidized form is active. Reduced SoxR was detected in overproducing strains by EPR spectroscopy of suspensions of intact cells. Oxidized Fe-S centers were determined by lysing the cells and treating them with the reducing agent sodium dithionite prior to EPR measurements. In uninduced cells, 90% of the SoxR was in the reduced form. Treatment with the redox cycling agents phenazine methosulfate or plumbagin was accompanied by reversible oxidation of the Fe-S centers. Mutant SoxR derivatives that were constitutively activated existed constitutively in an oxidized state. The results indicate the presence of a cellular pathway for countering the autooxidation of SoxR and confirm the hypothesis that induction of the regulon is mediated by a shift in the redox equilibrium of SoxR rather than by assembly of its Fe-S clusters.
SoxR蛋白是大肠杆菌soxRS（超氧化物应答）调节子的转录激活因子，含有可自动氧化的[2Fe-2S]中心，推测其作为氧化还原传感器。先前的体外转录实验表明只有氧化形式具有活性。通过完整细胞悬浮液的电子顺磁共振光谱法在过量表达菌株中检测到还原型SoxR。在电子顺磁共振测量之前，通过裂解细胞并用还原剂连二亚硫酸钠处理来测定氧化的铁硫中心。在未诱导的细胞中，90%的SoxR处于还原形式。用氧化还原循环剂硫酸吩嗪或白花丹素处理伴随着铁硫中心的可逆氧化。组成型激活的突变型SoxR衍生物以氧化状态组成型存在。结果表明存在一种对抗SoxR自动氧化的细胞途径，并证实了调节子的诱导是由SoxR氧化还原平衡的改变而非其铁硫簇的组装介导的这一假设。
