Institut Pasteur, Biology of Gram-Positive Pathogens, Department of Microbiology, 25 Rue du Docteur Roux, 75724 Paris Cedex 15, France.
Mol Microbiol. 2011 Aug;81(3):602-22. doi: 10.1111/j.1365-2958.2011.07735.x. Epub 2011 Jul 4.
Two-component systems (TCSs) are key regulatory pathways allowing bacteria to adapt their genetic expression to environmental changes. Bacitracin, a cyclic dodecylpeptide antibiotic, binds to undecaprenyl pyrophosphate, the lipid carrier for cell wall precursors, effectively inhibiting peptidoglycan biosynthesis. We have identified a novel and previously uncharacterized TCS in the major human pathogen Staphylococcus aureus that we show to be essential for bacitracin and nisin resistance: the BraS/BraR system (Bacitracin resistance associated; SA2417/SA2418). The braRS genes are located immediately upstream from genes encoding an ABC transporter, accordingly designated BraDE. We have shown that the BraSR/BraDE module is a key bacitracin and nisin resistance determinant in S. aureus. In the presence of low antibiotic concentrations, BraSR activate transcription of two operons encoding ABC transporters: braDE and vraDE. We identified a highly conserved imperfect palindromic sequence upstream from the braDE and vraDE promoter sequences, essential for their transcriptional activation by BraSR, suggesting it is the likely BraR binding site. We demonstrated that the two ABC transporters play distinct and original roles in antibiotic resistance: BraDE is involved in bacitracin sensing and signalling through BraSR, whereas VraDE acts specifically as a detoxification module and is sufficient to confer bacitracin and nisin resistance when produced on its own. We show that these processes require functional BraD and VraD nucleotide-binding domain proteins, and that the large extracellular loop of VraE confers its specificity in bacitracin resistance. This is the first example of a TCS associated with two ABC transporters playing separate roles in signal transduction and antibiotic resistance.
双组分系统（TCSs）是允许细菌适应环境变化的关键调节途径，使其能够调节其基因表达。杆菌肽是一种环状十二肽抗生素，与未端磷酸化的十一碳烯基焦磷酸结合，作为细胞壁前体的脂质载体，有效地抑制肽聚糖的生物合成。我们在主要的人类病原体金黄色葡萄球菌中发现了一个新的、以前未被描述的 TCS，我们证明它对抗生素杆菌肽和乳链菌肽的耐药性是必需的：BraS/BraR 系统（杆菌肽耐药相关；SA2417/SA2418）。BraRS 基因位于编码 ABC 转运体的基因的上游，相应地命名为 BraDE。我们已经表明，BraSR/BraDE 模块是金黄色葡萄球菌中抗杆菌肽和乳链菌肽的关键决定因素。在低抗生素浓度下，BraSR 激活编码 ABC 转运体的两个操纵子的转录：braDE 和 vraDE。我们在 braDE 和 vraDE 启动子序列的上游发现了一个高度保守的不完美的回文序列，对于 BraSR 的转录激活是必需的，这表明它可能是 BraR 的结合位点。我们证明了这两个 ABC 转运体在抗生素耐药性中发挥着独特而原始的作用：BraDE 通过 BraSR 参与杆菌肽的感应和信号转导，而 VraDE 则作为一个解毒模块发挥作用，当单独产生时足以赋予杆菌肽和乳链菌肽的耐药性。我们表明，这些过程需要功能性的 BraD 和 VraD 核苷酸结合域蛋白，并且 VraE 的大细胞外环赋予了其在杆菌肽耐药性中的特异性。这是第一个与两个 ABC 转运体相关的 TCS 分别在信号转导和抗生素耐药性中发挥作用的例子。
