Cystathionine γ-Lyase Is a Component of Cystine-Mediated Oxidative Defense in Lactobacillus reuteri BR11
Cystathionine γ-Lyase Is a Component of Cystine-Mediated Oxidative Defense in Lactobacillus reuteri BR11
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DOI：
10.1128/jb.01553-08
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发表时间：
2009-03-15
影响因子：
3.2
通讯作者：
Giffard, Philip M.
中科院分区：
文献类型：
--
作者：
Lo, Raquel;Turner, Mark S.;Giffard, Philip M.
罗伊氏乳杆菌BR11具有一种新的氧化防御机制，涉及cyuABC基因簇编码的丰富的胱氨酸ABC转运体。在CyuC转运体摄取胱氨酸时，会分泌大量硫醇，包括H2S。在一些罗伊氏乳杆菌菌株中，胱氨酸γ裂解酶（cystathionine γ - lysase, cgl）基因与cyu基因共转录，并被假设通过产生还原等量物参与胱氨酸介导的氧化防御。通过构建cgl突变体（PNG901），并将其与相似构建的cyuC突变体（PNG902）进行比较，在罗伊氏乳杆菌BR11中验证了这一假设。尽管胱氨酸生产H2S需要Cgl，但在de Mann-Rogosa-Sharpe培养基中，Cgl对氧化防御并不重要，与CyuC相反，CyuC的失活导致了充气培养中的滞后期停滞。Cgl在氧化防御中的重要性仅在血红蛋白存在时才被发现，血红蛋白会造成严重的氧化应激。在曝气培养中，两种突变体的生长缺陷都可以通过补充半胱氨酸（cgl突变体也是如此）而不是蛋氨酸来缓解，cyuC突变体对蛋氨酸的需求量要高得多。我们得出结论，罗伊氏乳杆菌BR11需要高浓度的外源半胱氨酸/胱氨酸才能在有氧条件下最佳生长。丰富的CyuC转运体满足了这一要求，这可能是由于Cgl具有广泛的底物特异性，导致CyuC转运体将胱氨酸降解为H2S的无效途径。Cgl在氧化防御中起着次要作用，其半胱氨酸生物合成的功能已得到充分证明。
Lactobacillus reuteri BR11 possesses a novel mechanism of oxidative defense involving an abundant cystine ABC transporter encoded by the cyuABC gene cluster. Large amounts of thiols, including H2S, are secreted upon cystine uptake by the CyuC transporter. A cystathionine gamma-lyase (cgl) gene is cotranscribed with the cyu genes in several L. reuteri strains and was hypothesized to participate in cystine-mediated oxidative defense by producing reducing equivalents. This hypothesis was tested with L. reuteri BR11 by constructing a cgl mutant (PNG901) and comparing it to a similarly constructed cyuC mutant (PNG902). Although Cgl was required for H2S production from cystine, it was not crucial for oxidative defense in de Mann-Rogosa-Sharpe medium, in contrast to CyuC, whose inactivation resulted in lag-phase arrest in aerated cultures. The importance of Cgl in oxidative defense was seen only in the presence of hemin, which poses severe oxidative stress. The growth defects in aerated cultures of both mutants were alleviated by supplementation with cysteine ( and cystine in the cgl mutant) but not methionine, with the cyuC mutant showing a much higher concentration requirement. We conclude that L. reuteri BR11 requires a high concentration of exogenous cysteine/cystine to grow optimally under aerobic conditions. This requirement is fulfilled by the abundant CyuC transporter, which has probably arisen due to the broad substrate specificity of Cgl, resulting in a futile pathway which degrades cystine taken up by the CyuC transporter to H2S. Cgl plays a secondary role in oxidative defense by its well-documented function of cysteine biosynthesis.