National Key Laboratory of Agricultural Microbiology, Center for Proteomics Research, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, China.
PLoS One. 2012;7(1):e30186. doi: 10.1371/journal.pone.0030186. Epub 2012 Jan 17.
Protection against oxidative stress is one of the primary defense mechanisms contributing to the survival of Mycobacterium tuberculosis in the host. In this study, we provide evidence that OxyS, a LysR-type transcriptional regulator functions as an oxidative stress response regulator in mycobacteria. Overexpression of OxyS lowers expression of the catalase-peroxidase (KatG) gene in M. smegmatis. OxyS binds directly with the katG promoter region and a conserved, GC-rich T-N(11)-A motif for OxyS binding was successfully characterized in the core binding site. Interestingly, the DNA-binding activity of OxyS was inhibited by H(2)O(2), but not by dithiothreitol. Cys25, which is situated at the DNA-binding domain of OxyS, was found to have a regulatory role for the DNA-binding ability of OxyS in response to oxidative stress. In contrast, the other three cysteine residues in OxyS do not appear to have this function. Furthermore, the mycobacterial strain over-expressing OxyS had a higher sensitivity to H(2)O(2). Thus, OxyS responds to oxidative stress through a unique cysteine residue situated in its DNA-binding domain and negatively regulates expression of the katG gene. These findings uncover a specific regulatory mechanism for mycobacterial adaptation to oxidative stress.
抵御氧化应激是分枝杆菌在宿主体内生存的主要防御机制之一。在本研究中，我们提供的证据表明，LysR 型转录调节子 OxyS 作为一种氧化应激反应调节剂在分枝杆菌中发挥作用。OxyS 的过表达降低了 M. smegmatis 中过氧化氢酶过氧化物酶（KatG）基因的表达。OxyS 直接与 katG 启动子区域结合，并且成功地鉴定了核心结合位点中保守的富含 GC 的 T-N(11)-A 基序用于 OxyS 结合。有趣的是，OxyS 的 DNA 结合活性被 H(2)O(2)抑制，但不受二硫苏糖醇抑制。位于 OxyS 的 DNA 结合域的 Cys25 被发现对 OxyS 的 DNA 结合能力具有调节作用，以响应氧化应激。相比之下，OxyS 中的其他三个半胱氨酸残基似乎没有此功能。此外，过表达 OxyS 的分枝杆菌菌株对 H(2)O(2)的敏感性更高。因此，OxyS 通过位于其 DNA 结合域中的独特半胱氨酸残基响应氧化应激，并负调控 katG 基因的表达。这些发现揭示了分枝杆菌适应氧化应激的特定调节机制。
