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Journal of Bacteriology, March 2001, p. 1961-1973, Vol. 183, No. 6
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.6.1961-1973.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Essential Thioredoxin-Dependent Peroxiredoxin System from Helicobacter pylori: Genetic and Kinetic Characterization

Laura M. S. Baker,1 Ausra Raudonikiene,2,dagger Paul S. Hoffman,2 and Leslie B. Poole1,*

Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina,1 and Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada2

Received 18 October 2000/Accepted 3 January 2001

Helicobacter pylori, an oxygen-sensitive microaerophile, contains an alkyl hydroperoxide reductase homologue (AhpC, HP1563) that is more closely related to 2-Cys peroxiredoxins of higher organisms than to most other eubacterial AhpC proteins. Allelic replacement mutagenesis revealed ahpC to be essential, suggesting a critical role for AhpC in defending H. pylori against oxygen toxicity. Characterization of the ahpC promoter region divulged two putative regulatory elements and identified the transcription initiation site, which was mapped to 96 and 94 bp upstream of the initiation codon. No homologue of ahpF, which encodes the dedicated AhpC reductase in most eubacteria, was found in the H. pylori genome. Instead, homologues of Escherichia coli thioredoxin (Trx) reductase (TrxR, HP0825) and Trx (Trx1, HP0824) formed a reductase system for H. pylori AhpC. A second Trx homologue (Trx2, HP1458) was identified but was incapable of AhpC reduction, although Trx2 exhibited disulfide reductase activity with other substrates [insulin and 5,5'-dithiobis(2-nitrobenzoic acid)]. AhpC interactions with each substrate, Trx1 and hydroperoxide, were bimolecular and nonsaturable (infinite Vmax and Km values) but rapid enough (at 1 × 105 to 2 × 105 M-1 s-1) to suggest an important role for AhpC in cellular peroxide metabolism. AhpC also exhibited a wide specificity for hydroperoxide substrates, which, taken together with the above results, suggests a minimal binding site for hydroperoxides composed of little more than the cysteinyl (Cys49) active site. H. pylori AhpC was not reduced by Salmonella typhimurium AhpF and was slightly more active with E. coli TrxR and Trx1 than was S. typhimurium AhpC, demonstrating the specialized catalytic properties of this peroxiredoxin.

* Corresponding author. Mailing address: Wake Forest University School of Medicine, Department of Biochemistry, Medical Center Blvd., Winston-Salem, NC 27157. Phone: (336) 716-6711. Fax: (336) 716-7671. E-mail: lbpoole{at}wfubmc.edu.

dagger Present address: Aventis Pasteur Ltd., Toronto, Ontario M2R 3T4, Canada.

Journal of Bacteriology, March 2001, p. 1961-1973, Vol. 183, No. 6
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.6.1961-1973.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.