Lee Kang-Lok, Singh Atul K, Heo Lim, Seok Chaok, Roe Jung-Hye
Laboratory of Molecular Microbiology, School of Biological Sciences, and Institute of Microbiology, Seoul National University, Seoul, 151-742, Korea.
Department of Chemistry, Seoul National University, Seoul, 151-747, Korea.
Mol Microbiol. 2015 Sep;97(5):808-21. doi: 10.1111/mmi.13068. Epub 2015 Jun 12.
SoxR is a [2Fe-2S]-containing sensor-regulator, which is activated through oxidation by redox-active compounds (RACs). SoxRs show differential sensitivity to RACs, partly due to different redox potentials, such that Escherichia coli (Ec) SoxR with lower potential respond to broader range of RACs than Streptomyces coelicolor (Sc) SoxR. In S. coelicolor, the RACs that do not activate ScSoxR did not inhibit growth, suggesting that ScSoxR is tuned to respond to growth-inhibitory RACs. Based on sequence comparison and mutation studies, two critical amino acids around the [2Fe-2S] binding site were proposed as key determinants of sensitivity. ScSoxR-like mutation (R127L/P131V) in EcSoxR changed its sensitivity profile as ScSoxR, whereas EcSoxR-like mutation (L126R/V130P) in ScSoxR caused relaxed response. In accordance, the redox potentials of EcSoxR(R) (127) (L) (/) (P) (131) (V) and ScSoxR(L126R/V130P) were estimated to be -192 ± 8 mV and -273 ± 10 mV, respectively, approaching that of ScSoxR (-185 mV) and EcSoxR (-290 mV). Molecular dynamics simulations revealed that the R127L and P131V substitutions in EcSoxR caused more electropositive environment around [2Fe-2S], making it harder to get oxidized. This reveals a mechanism to modulate redox-potential in [Fe-S]-containing sensors by point mutations and to evolve a sensor with differential sensitivity to achieve optimal cellular physiology.
SoxR是一种含[2Fe-2S]的传感调节蛋白，通过被氧化还原活性化合物（RACs）氧化而被激活。SoxRs对RACs表现出不同的敏感性，部分原因是氧化还原电位不同，因此具有较低电位的大肠杆菌（Ec）SoxR比天蓝色链霉菌（Sc）SoxR对更广泛的RACs有反应。在天蓝色链霉菌中，不激活ScSoxR的RACs不会抑制生长，这表明ScSoxR被调节为对抑制生长的RACs做出反应。基于序列比较和突变研究，[2Fe-2S]结合位点周围的两个关键氨基酸被认为是敏感性的关键决定因素。EcSoxR中的ScSoxR样突变（R127L/P131V）改变了其敏感性，使其与ScSoxR相同，而ScSoxR中的EcSoxR样突变（L126R/V130P）则导致反应松弛。相应地，EcSoxR(R) (127) (L) (/) (P) (131) (V)和ScSoxR(L126R/V130P)的氧化还原电位估计分别为-192±8 mV和-273±10 mV，接近ScSoxR（-185 mV）和EcSoxR（-290 mV）。分子动力学模拟表明，EcSoxR中的R127L和P131V取代导致[2Fe-2S]周围的正电环境增加，使其更难被氧化。这揭示了一种通过点突变调节含[Fe-S]传感器氧化还原电位的机制，并进化出一种具有不同敏感性的传感器以实现最佳细胞生理功能。
