The role of glutathionylspermidine amidase in redox regulation of Escherichia coli
Date Issued
2009
Date
2009
Author(s)
Chen, Tzu-Chieh
Abstract
Glutathionylspermidine (Gsp), the conjugate of glutathione and spermidine, only appears in some parasitical protozoa or bacteria such as Escherichia coli. Therefore, the enzymes involved in Gsp metabolism are considered as the targets for anti-parasitic drugs. Glutathionylspermidine synthetase/amidase (GspSA) is a bifunctional enzyme to catalyze the biosynthesis and hydrolysis of Gsp shown as follows. Although GspSA was identified in Escharichia coli more than a decade ago, several issues still remain ambiguous. For instance, the physiological functions of Gsp and GspSA in E. coli are not clear. There is no clear answer regarding to how the two opposite activities of GspSA (Gsp synthetase and Gsp amidase) communicate. In the previous study, Gsp amidase was found to be selectively inactivated in the presence of hydrogen peroxide (H2O2) owing to temporary oxidation of cysteine-59 in the active site. In contrast, the activity of Gsp synthetase remained intact. In order to understand the regulation of GspSA and the Gsp turnover, a sensitive method was thus developed for monitoring the amount of small thiols by derivatization with mBBr, followed by HPLC analysis. In the in vitro and in vivo study, the Gsp level was found to be accumulative due to selective inactivation of Gsp amidase by H¬2O2, in contrast to the constant expression level of GspSA. In addition, Gsp was also found to increase under starvation or anaerobic conditions. A GspSA-based model was proposed to interpret how E. coli regulates the intracellular redox balance under oxidative stress. In addition to explaining how selective inactivation of Gsp amidase leading to the accumulation of Gsp, the model also demonstrates that Gsp disulfide, the oxidative form of Gsp, could be regenerated to GSH and spermidine by the Gsp amidase and GSH reductase couple.
Subjects
glutathionylspermidine
glutathione
oxidative stress
redox
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