Shimizu Takayuki, Shen Jiangchuan, Fang Mingxu, Zhang Yixiang, Hori Koichi, Trinidad Jonathan C, Bauer Carl E, Giedroc David P, Masuda Shinji
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Kanagawa 226-8501, Japan.
Department of Chemistry, Indiana University, Bloomington, IN 47405-7102.
Proc Natl Acad Sci U S A. 2017 Feb 28;114(9):2355-2360. doi: 10.1073/pnas.1614133114. Epub 2017 Feb 14.
Sulfide was used as an electron donor early in the evolution of photosynthesis, with many extant photosynthetic bacteria still capable of using sulfur compounds such as hydrogen sulfide (HS) as a photosynthetic electron donor. Although enzymes involved in HS oxidation have been characterized, mechanisms of regulation of sulfide-dependent photosynthesis have not been elucidated. In this study, we have identified a sulfide-responsive transcriptional repressor, SqrR, that functions as a master regulator of sulfide-dependent gene expression in the purple photosynthetic bacterium SqrR has three cysteine residues, two of which, C41 and C107, are conserved in SqrR homologs from other bacteria. Analysis with liquid chromatography coupled with an electrospray-interface tandem-mass spectrometer reveals that SqrR forms an intramolecular tetrasulfide bond between C41 and C107 when incubated with the sulfur donor glutathione persulfide. SqrR is oxidized in sulfide-stressed cells, and tetrasulfide-cross-linked SqrR binds more weakly to a target promoter relative to unmodified SqrR. C41S and C107S SqrRs lack the ability to respond to sulfide, and constitutively repress target gene expression in cells. These results establish that SqrR is a sensor of HS-derived reactive sulfur species that maintain sulfide homeostasis in this photosynthetic bacterium and reveal the mechanism of sulfide-dependent transcriptional derepression of genes involved in sulfide metabolism.
在光合作用进化的早期，硫化物被用作电子供体，许多现存的光合细菌仍然能够利用硫化氢（HS）等硫化合物作为光合电子供体。尽管参与HS氧化的酶已得到表征，但硫化物依赖性光合作用的调控机制尚未阐明。在本研究中，我们鉴定了一种硫化物响应转录阻遏物SqrR，它作为紫色光合细菌中硫化物依赖性基因表达的主要调节因子发挥作用。SqrR有三个半胱氨酸残基，其中两个，即C41和C107，在来自其他细菌的SqrR同源物中是保守的。液相色谱与电喷雾接口串联质谱联用分析表明，当与硫供体谷胱甘肽过硫化物一起孵育时，SqrR在C41和C107之间形成分子内四硫键。SqrR在受到硫化物胁迫的细胞中被氧化，相对于未修饰的SqrR，四硫键交联的SqrR与靶启动子的结合更弱。C41S和C107S SqrR缺乏对硫化物作出反应的能力，并在细胞中组成性地抑制靶基因表达。这些结果表明，SqrR是HS衍生的活性硫物种的传感器，可维持这种光合细菌中的硫化物稳态，并揭示了参与硫化物代谢的基因的硫化物依赖性转录去抑制机制。
