Hung Jacky, Cooper Dee, Turner Mark S, Walsh Terry, Giffard Philip M
Infectious Disease Program, Faculty of Science, Queensland University of Technology, G.P.O. Box 2434, Brisbane, Qld 4001, Australia.
FEMS Microbiol Lett. 2003 Oct 10;227(1):93-9. doi: 10.1016/S0378-1097(03)00653-0.
BspA is an abundant surface protein from Lactobacillus fermentum BR11, and is required for normal cystine uptake. In previous studies, a mutant strain deficient in BspA (L. fermentum PNG201) was found to be sensitive to oxidative stress. In this study, the biochemical basis for this was explored. It was found that under aerobic batch culture conditions in de Mann-Rogosa-Sharpe medium, both L. fermentum BR11 and PNG201 entered stationary phase due to hydrogen peroxide accumulation. However, this took place at a lower optical density for PNG201 than for BR11. Measurements of hydrogen peroxide levels revealed that the BspA mutant strain overproduces this compound. Addition of 6 mM cystine to aerobic cultures was found to prevent hydrogen peroxide production by both the BR11 and PNG201 strains, but lower cystine concentrations depressed hydrogen peroxide production in BR11 more efficiently than in PNG201. Each mole of cystine was able to prevent the production of several moles of hydrogen peroxide by L. fermentum BR11, suggesting that hydrogen peroxide breakdown is dependent upon a thiol that cycles between reduced and oxidized states. It was concluded that peroxide breakdown by L. fermentum BR11 is dependent upon exogenous cystine. It is most probable that the imported L-cystine is catabolized by a cystathionine lyase and then converted into a thiol reductant for a peroxidase.
BspA是发酵乳杆菌BR11中一种丰富的表面蛋白，是正常摄取胱氨酸所必需的。在先前的研究中，发现缺乏BspA的突变菌株（发酵乳杆菌PNG201）对氧化应激敏感。在本研究中，探讨了其生化基础。发现在德氏-罗氏-夏普培养基中的好氧分批培养条件下，由于过氧化氢的积累，发酵乳杆菌BR11和PNG201均进入稳定期。然而，PNG201达到稳定期时的光密度低于BR11。过氧化氢水平的测量显示，BspA突变菌株过量产生这种化合物。发现在好氧培养物中添加6 mM胱氨酸可防止BR11和PNG201菌株产生过氧化氢，但较低的胱氨酸浓度对BR11中过氧化氢产生的抑制作用比对PNG201更有效。每摩尔胱氨酸能够防止发酵乳杆菌BR11产生几摩尔过氧化氢，这表明过氧化氢的分解依赖于一种在还原态和氧化态之间循环的硫醇。得出的结论是，发酵乳杆菌BR11的过氧化物分解依赖于外源性胱氨酸。很可能导入的L-胱氨酸被胱硫醚裂解酶分解代谢，然后转化为过氧化物酶的硫醇还原剂。
