Kinetics studies of the superoxide-mediated electron transfer reactions between rubredoxin-type proteins and superoxide reductases

Abstract

In this work we present a kinetic study of the superoxide-mediated electron transfer reactions between rubredoxin-type proteins and members of the three different classes of superoxide reductases (SORs). SORs from the sulfate-reducing bacteria Desulfovibrio vulgaris (Dv) and D. gigas (Dg) were chosen as prototypes of classes I and II, respectively, while SOR from the syphilis spyrochete Treponema pallidum (Tp) was representative of class III. Our results show evidence for different behaviors of SORs toward electron acceptance, with a trend to specificity for the electron donor and acceptor from the same organism. Comparison of the different k app values, 176.9±25.0 min À1 in the case of the Tp/Tp electron transfer, 31.8±3.6 min À1 for the Dg/ Dg electron transfer, and 6.9±1.3 min À1 for Dv/Dv, could suggest an adaptation of the superoxide-mediated electron transfer efficiency to various environmental conditions. We also demonstrate that, in Dg, another iron-sulfur protein, a desulforedoxin, is able to transfer electrons to SOR more efficiently than rubredoxin, with a k app value of 108.8±12.0 min À1 , and was then assigned as the potential physiological electron donor in this organism.

Crystal Structure of the Tp34 (TP0971) Lipoprotein of Treponema pallidum

“…T. pallidum lacks major iron-containing proteins typically found in other bacterial pathogens, including the oxidative defense enzymes superoxide dismutase, catalase, and peroxidase (65). However, the spirochete is believed to contain superoxide reductase (Tp0823) and rubredoxin (Tp0991), both of which are likely to participate in oxygen detoxification (50,(82)(83)(84). This is consistent with the prevailing view that T. pallidum is microaerophilic (1).…”

Intermolecular electron transfer in two-iron superoxide reductase: a putative role for the desulforedoxin center as an electron donor to the iron active site

“…In bacteria where SOR is naturally expressed, rubredoxin [23][24][25][26][27] and desulforedoxin [27] have been the only SOR electron donors identified so far. Whereas the specific involvement of desulforedoxin in an electron transport chain remains to be documented, in the case of sulfate reducing bacteria, rubredoxin is thought to act as an electron relay between the NADH:rubredoxin oxidoreductase (Nro) and several metalloproteins involved in ROS detoxification [10].…”

“…In particular, it is not known yet whether SOR uses specific electron donors to reduce superoxide or if the enzyme has the capability to use a wide panel of electron sources, favoring a superoxide detoxification activity independent of a specific electron transfer pathway. Whereas cellular reductase enzymes directly involved in the SOR reduction pathway have not been identified yet, two small electron transfer proteins rubredoxin (Rub) [23][24][25][26] and desulforedoxin (Dx) [27] have been shown to efficiently transfer electrons to the ferric SOR active site. For 5 rubredoxin, these results are consistent with the fact that in several bacterial genomes, sor and rub genes have been found to be encoded within the same operon.…”

O 2 and Reactive Oxygen Species Detoxification Complex, Composed of O 2 -Responsive NADH:Rubredoxin Oxidoreductase-Flavoprotein A2-Desulfoferrodoxin Operon Enzymes, Rubperoxin, and Rubredoxin, in Clostridium acetobutylicum

“…The reaction of xanthine and XOD gener- (6). The superoxide anion flux was determined as equal to the rate of reduction of cytochrome c (1,25). The calculated rate of the superoxide anion flux generated by 0.5 mM xanthine and 1 l of purchased XOD added to 1 ml of a reaction mixture was 8.1 Ϯ 0.3 M/min.…”