Superoxide reductase as a unique defense system against superoxide stress in the microaerophile Treponema pallidum

Aerobic life requires the presence of antioxidant enzymes, such as superoxi de dismutase, catalase, and per oxidase to eliminate deleterious oxygen der ivatives, Treponema pallidum, a microaerophilic bacterium responsible for v enereal syphilis, is an interesting organism because it lacks all of the ab ove-mentioned enzymes, as deduced from its recently sequenced genome. In th is paper, we describe a gene in T. pallidum with sequence homologies to a n ew class of antioxidant systems, named superoxide reductases, recently isol ated from sulfate-reducing bacteria (Lombard, M., Fontecave, M., Touati, D. , and Niviere, V. (2000) J. Biol. Chem. 275, 115-121). We report that (i) e xpression of the T. pallidum gene fully restored to a superoxide dismutase- deficient Escherichia coli mutant the ability to grow under aerobic conditi ons; (ii) the corresponding protein displays a strong superoxide reductase activity; and (iii) the T. pallidum protein contains only one mononuclear n onheme ferrous center, able to reduce superoxide selectively and efficientl y, whereas previously characterized superoxide reductase from Desulfoarculu s baarsii contains an additional rubredoxin-like ferric center. These resul ts suggest that T, pallidum antioxidant defenses rely on a new class of sup eroxide reductase and raise the question of the importance of superoxide re ductases in mechanisms for detoxifying superoxide radicals.