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Journal of Biochemistry Advance Access published online on January 7, 2008
Journal of Biochemistry, doi:10.1093/jb/mvm247
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© 2008 The Japanese Biochemical Society

Selenite assimilation into formate dehydrogenase H depends on thioredoxin reductase in Escherichia coli

Muneaki Takahata*, Takashi Tamura*,{ddagger}, Katsumasa Abe#, Hisaaki Mihara#, Suguru Kurokawa#, Yoshihiro Yamamoto{dagger}, Ryuhei Nakano, Nobuyoshi Esaki# and Kenji Inagaki

Department of Biofunctional Chemistry, Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530, Japan
# Laboratory of Molecular Microbial Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
{dagger} Department of Genetics, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya, Hyogo 663-8501, Japan

{ddagger}To whom correspondence should be addressed: Dr. Takashi Tamura, Fax: + 81-86-251-8388, E-mail: tktamura{at}cc.okayama-u.ac.jp

Received October 18, 2007; Accepted December 9, 2007


  Abstract

Escherichia coli growing under anaerobic conditions produces H2 and CO2 by the enzymatic cleavage of formate that is produced from pyruvate at the end of glycolysis. Selenium is an integral part of formate dehydrogenase H (FDHH), which catalyzes the first step in the formate hydrogen lyase (FHL) system. The genes of FHL system are transcribed only under anaerobic conditions, in the presence of a {sigma}54-dependent transcriptional activator FhlA that binds formate as an effector molecule. Although the formate addition to the nutrient media has been an established procedure for inducing high FDHH activity, we have identified a low-salt nutrient medium containing < 0.1% NaCl enabled constitutive, high expression of FDHH even without formate and D-glucose added to the medium. The novel conditions allowed us to study the effects of disrupting genes like trxB (thioredoxin reductase) or gor (glutathione reductase) on the production of FDHH activity and also reductive assimilation of selenite (SeO32-) into the selenoprotein. Despite the widely-accepted hypothesis that selenite is reduced by glutathione reductase-dependent system, it was demonstrated that trxB gene was essential for FDHH production and for labeling the FDHH polypeptide with 75Se-selenite. Our present study reports for the first time the physiological involvement of thioredoxin reductase in the reductive assimilation of selenite in E. coli.

Key Words: formate dehydrogenase H, thioredoxin reductase, selenite assimilation

* M.T. and T.T. contributed equally to this work.


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