Journal of Biological Chemistry
Volume 275, Issue 37, 15 September 2000, Pages 28439-28448
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GENOMICS PROTEOMICS AND BIOINFORMATICS
Neelaredoxin, an Iron-binding Protein from the Syphilis Spirochete, Treponema pallidum, Is a Superoxide Reductase*

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Treponema pallidum, the causative agent of venereal syphilis, is a microaerophilic obligate pathogen of humans. As it disseminates hematogenously and invades a wide range of tissues, T. pallidum presumably must tolerate substantial oxidative stress. Analysis of the T. pallidumgenome indicates that the syphilis spirochete lacks most of the iron-binding proteins present in many other bacterial pathogens, including the oxidative defense enzymes superoxide dismutase, catalase, and peroxidase, but does possess an orthologue (TP0823) for neelaredoxin, an enzyme of hyperthermophilic and sulfate-reducing anaerobes shown to possess superoxide reductase activity. To analyze the potential role of neelaredoxin in treponemal oxidative defense, we examined the biochemical, spectroscopic, and antioxidant properties of recombinant T. pallidum neelaredoxin. Neelaredoxin was shown to be expressed in T. pallidum by reverse transcriptase-polymerase chain reaction and Western blot analysis. Recombinant neelaredoxin is a 26-kDa α2 homodimer containing, on average, 0.7 iron atoms/subunit. Mössbauer and EPR analysis of the purified protein indicates that the iron atom exists as a mononuclear center in a mixture of high spin ferrous and ferric oxidation states. The fully oxidized form, obtained by the addition of K3(Fe(CN)6), exhibits an optical spectrum with absorbances at 280, 320, and 656 nm; the last feature is responsible for the protein's blue color, which disappears upon ascorbate reduction. The fully oxidized protein has aA 280/A 656 ratio of 10.3. Enzymatic studies revealed that T. pallidumneelaredoxin is able to catalyze a redox equilibrium between superoxide and hydrogen peroxide, a result consistent with it being a superoxide reductase. This finding, the first description of a T. pallidum iron-binding protein, indicates that the syphilis spirochete copes with oxidative stress via a primitive mechanism, which, thus far, has not been described in pathogenic bacteria.

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Published, JBC Papers in Press, June 26, 2000, DOI 10.1074/jbc.M003314200

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This work was supported by National Institutes of Health Grants AI 26756 (to J. D. R.) and GM58778 (to B. H. H.), by PRAXIS XXI (to C. A., I. M., and J. J. G. M.), and by support from the Mayo Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.