Conformational change of DNA bound to transcription factor response to environmental change

[2Fe-2S]转录因子SoxR在大肠杆菌中作为氧化应激的感受器发挥作用。在氧化状态，转录是通过扭曲目标DNA启动子区域来激活的，以启动RNA聚合酶的转录，而蛋白质的非活性还原状态仍然没有特征。通过用荧光探针2-氨基嘌呤(2AP)和吡咯-DC分别定点替换启动子寡核苷酸的腺嘌呤和胞嘧啶碱基，直接观察到启动子DNA氧化还原依赖的构象变化。SoxR-DNA复合体中[2Fe-2S]团簇的减少显著减弱了DNA中心部分结合的2AP部分的荧光强度。这些结果有力地表明，氧化还原的变化导致了DNA启动子区域中心A-T碱基对区域内的大的构象变化。

The [2Fe-2S] transcriptional factor SoxR functions as a sensor of oxidative stress in Escherichia coli. In the oxidized state, transcription is activated by distorting the target DNA promoter region to initiate transcription by RNA polymerase, while the inactive reduced state of the protein remains uncharacterized. The redox-dependent conformational change of the promoter DNA was directly observed by site-specifically replacing the adenine and cytosine bases of the promoter oligonucleotide with the fluorescent probes 2-aminopurine (2Ap) and pyrrolo-dC, respectively. Reduction of the [2Fe-2S] cluster in SoxR-DNA complex dramatically weakened the fluorescence intensity of the 2Ap moieties incorporated into the central part of the DNA. These results strongly suggested that the redox change caused a large conformational change within the region confined to the central A-T base pairs in the promoter region of the DNA.