Repairing oxidized proteins in the bacterial envelope using respiratory chain electrons
作者:Alexandra Gennaris、Benjamin Ezraty、Camille Henry、Rym Agrebi、Alexandra Vergnes、Emmanuel Oheix、Julia Bos、Pauline Leverrier、Leon Espinosa、Joanna Szewczyk、Didier Vertommen、Olga Iranzo、Jean-François Collet、Frédéric Barras
DOI:10.1038/nature15764
日期:2015.12
The identification of an enzymatic system repairing proteins containing oxidized methionine in the bacterial cell envelope, a compartment particularly susceptible to oxidative damage by host defence mechanisms. Frédéric Barras and colleagues report the identification of an enzyme system, MsrPQ, which repairs a wide range of periplasmic proteins with oxidatively damaged methionine (methionine sulfoxide, Met-O) in the bacterial cell envelope, a compartment that is particularly susceptible to oxidative damage by host defence mechanisms. MsrP and MsrQ are widely distributed in Gram-negative bacteria and are expressed following exposure to hypochlorous acid, a powerful antimicrobial agent that is released by neutrophils. Interestingly, the MsrPQ repair system is functionally distinct from conventional methionine sulfoxide reductases as it exhibits non-stereospecificity and can reduce both R- and S-diastereoisomers of Met-O. Furthermore, the authors report a novel mechanism of action for MsrPQ in which electrons from the respiratory chain are used for reducing power, establishing a new link between metabolism and cellular integrity. The reactive species of oxygen and chlorine damage cellular components, potentially leading to cell death. In proteins, the sulfur-containing amino acid methionine is converted to methionine sulfoxide, which can cause a loss of biological activity. To rescue proteins with methionine sulfoxide residues, living cells express methionine sulfoxide reductases (Msrs) in most subcellular compartments, including the cytosol, mitochondria and chloroplasts1,2,3. Here we report the identification of an enzymatic system, MsrPQ, repairing proteins containing methionine sulfoxide in the bacterial cell envelope, a compartment particularly exposed to the reactive species of oxygen and chlorine generated by the host defence mechanisms. MsrP, a molybdo-enzyme, and MsrQ, a haem-binding membrane protein, are widely conserved throughout Gram-negative bacteria, including major human pathogens. MsrPQ synthesis is induced by hypochlorous acid, a powerful antimicrobial released by neutrophils. Consistently, MsrPQ is essential for the maintenance of envelope integrity under bleach stress, rescuing a wide series of structurally unrelated periplasmic proteins from methionine oxidation, including the primary periplasmic chaperone SurA. For this activity, MsrPQ uses electrons from the respiratory chain, which represents a novel mechanism to import reducing equivalents into the bacterial cell envelope. A remarkable feature of MsrPQ is its capacity to reduce both rectus (R-) and sinister (S-) diastereoisomers of methionine sulfoxide, making this oxidoreductase complex functionally different from previously identified Msrs. The discovery that a large class of bacteria contain a single, non-stereospecific enzymatic complex fully protecting methionine residues from oxidation should prompt a search for similar systems in eukaryotic subcellular oxidizing compartments, including the endoplasmic reticulum.
鉴定出一种酶系统可修复细菌细胞包膜中含有氧化蛋氨酸的蛋白质,而细菌细胞包膜是一个特别容易受到宿主防御机制氧化损伤的区域。Frédéric Barras及其同事报告了一种酶系统MsrPQ的鉴定结果,该酶系统可修复细菌细胞包膜中含有氧化损伤的蛋氨酸(蛋氨酸亚砜,Met-O)的多种包膜蛋白质,而细菌细胞包膜是一个特别容易受到宿主防御机制氧化损伤的区域。MsrP 和 MsrQ 广泛分布于革兰氏阴性细菌中,在接触中性粒细胞释放的强效抗菌剂次氯酸后会表达。有趣的是,MsrPQ 修复系统在功能上有别于传统的蛋氨酸亚砜还原酶,因为它表现出非立体特异性,可以还原 Met-O 的 R-和 S-非对映异构体。此外,作者还报告了 MsrPQ 的一种新作用机制,即利用呼吸链中的电子进行还原,从而在新陈代谢和细胞完整性之间建立起一种新的联系。氧和氯的活性物种会破坏细胞成分,可能导致细胞死亡。在蛋白质中,含硫氨基酸蛋氨酸会转化为蛋氨酸亚砜,从而导致生物活性丧失。为了挽救含有蛋氨酸亚砜残基的蛋白质,活细胞在大多数亚细胞区室(包括细胞质、线粒体和叶绿体)中都表达蛋氨酸亚砜还原酶(Msrs)1,2,3。在这里,我们报告了一种酶系统--MsrPQ--的发现,它能修复细菌细胞包膜中含有蛋氨酸亚砜的蛋白质,而细菌细胞包膜是一个特别容易受到宿主防御机制产生的氧和氯等活性物种影响的区室。MsrP 是一种钼酵素,MsrQ 是一种血红素结合膜蛋白,它们在革兰氏阴性细菌(包括主要的人类病原体)中广泛保守。次氯酸是中性粒细胞释放的一种强力抗菌剂,可诱导 MsrPQ 的合成。在漂白压力下,MsrPQ 对维持包膜完整性至关重要,它能从蛋氨酸氧化中挽救一系列结构上不相关的包膜蛋白质,包括主要的包膜伴侣 SurA。为了实现这种活性,MsrPQ 使用了来自呼吸链的电子,这是一种将还原等价物导入细菌细胞包膜的新机制。MsrPQ 的一个显著特点是它有能力还原蛋氨酸亚砜的直向(R-)和阴向(S-)非对映异构体,这使得这种氧化还原酶复合物在功能上有别于以前发现的 Msrs。 发现一大类细菌含有一种单一的、非立体特异性的酶复合物,能完全保护蛋氨酸残基不被氧化,这应促使人们在真核生物亚细胞氧化区(包括内质网)中寻找类似的系统。