Spx-dependent oxygen sensing mechanism in lactic acid bacteria

在本研究中，我们分析了变形链球菌Spx依赖的氧敏机制。SPX是最初在枯草芽孢杆菌中发现的一种RNA结合蛋白。变形链球菌SpxA和SpxB在半胱氨酸残基被氧化时与RNA聚合酶的α-亚基结合更强。对细胞Spx降解途径的分析表明，SpxB被ClpXP酶复合体降解，而细胞内SpxA浓度恒定，不受ClpXP酶的影响。在clpPor clpX突变体中，SpxB浓度的增加并不影响抗氧化蛋白的表达。这些结果表明，半胱氨酸的氧化减少了Spx的残留量，而不是细胞Spx的浓度，这可能在变形链球菌的氧敏中起关键作用。

In thepresent study, we analyzed Spx-dependent oxygensensing mechanism of Streptococcus mutans. Spx is a RNA-binding protein originally identified in Bacillus subtilis. Both SpxA and SpxB of S. mutanswere shown to more strongly bind to alpha-subunit of RNA polymerase when cysteineresidues of these proteins were oxidized. Analysis of cellular Spx degradation pathway demonstrated that SpxB was degraded by ClpXP protease complexwhilecellular SpxA concentrations were constant and not affected by ClpXP protease. Increased concentrationsof SpxB in clpPor clpXmutant didn't affect the expression profileof antioxidative proteins. Theseresultsindicated that the oxidation of cysteineresidues of Spx, rather than cellularSpx concentrations, might play a critical role in oxygen sensing of S. mutans.