Spx is a major regulator of stress responses in Firmicutes. In Streptococcus mutans , two Spx homologues, SpxA1 and SpxA2, were identified as mediators of oxidative stress responses but the regulatory circuits controlling their levels and activity are presently unknown. Comparison of SpxA1 and SpxA2 protein sequences revealed differences at the C‐terminal end, with SpxA1 containing an unusual number of acidic residues. Here, we showed that a green fluorescence protein (GFP) reporter becomes unstable when fused to the last 10 amino acids of SpxA2 but remained stable when fused to the C‐terminal acidic tail of SpxA1. Inactivation of clpP or simultaneous inactivation of clpC and clpE stabilized the GFP::SpxA2_tail fusion protein. Addition of acidic amino acids to the GFP::SpxA2_tail chimera stabilized GFP, while deletion of the acidic residues destabilized GFP::SpxA1_tail. Promoter reporter fusions revealed that spxA1 transcription is co‐repressed by the metalloregulators PerR and SloR while spxA2 transcription is largely dependent on the envelope stress regulator LiaFSR. In agreement with spxA2 being part of the LiaR regulon, SpxA2 was found to be critical for the growth of S. mutans under envelope stress conditions. Finally, we showed that redox sensing is essential for SpxA1‐dependent activation of oxidative stress responses but dispensable for SpxA2‐mediated envelope stress responses.

中文翻译：

---

控制变形链球菌Spx水平的调节电路。

Spx是Firmicutes中压力反应的主要调节器。在变形链球菌中，两个Spx同源物SpxA1和SpxA2被确定为氧化应激反应的介体，但目前尚不清楚控制其水平和活性的调节电路。SpxA1和SpxA2蛋白序列的比较揭示了C末端的差异，其中SpxA1包含异常数量的酸性残基。在这里，我们显示了绿色荧光蛋白（GFP）报告基因与SpxA2的最后10个氨基酸融合时变得不稳定，而与SpxA1的C末端酸性尾端融合时则保持稳定。的失活CLPP或同时失活CLPC和clpE稳定GFP :: SpxA2_尾融合蛋白。向GFP :: SpxA2_尾部嵌合体添加酸性氨基酸可稳定GFP，而删除酸性残基则使GFP :: SpxA1_尾部不稳定。启动子记者融合显示，spxA1转录被金属调节剂PerR和SloR共抑制，而spxA2转录在很大程度上取决于包膜应激调节剂LiaFSR。与spxA2是LiaR regulon的一部分相一致，发现SpxA2对于包膜胁迫条件下的变形链球菌生长至关重要。最后，我们表明，氧化还原感测对于SpxA1依赖性的氧化应激反应激活至关重要，但对于SpxA2介导的包膜应激反应却是必不可少的。