Reaction of the desulfoferrodoxin from Desulfoarculus baarsii with superoxide anion. Evidence for a superoxide reductase activity

TL;DR

This study reveals that desulfoferrodoxin from Desulfoarculus baarsii acts as a superoxide reductase, providing a new antioxidant mechanism distinct from superoxide dismutase, with implications for oxidative stress protection.

Contribution

The paper demonstrates that desulfoferrodoxin functions as a superoxide reductase, offering a novel insight into bacterial oxidative stress defense mechanisms.

Findings

Desulfoferrodoxin exhibits weak superoxide dismutase activity.

Ferrous center reduces superoxide with high efficiency.

E. coli extracts can reduce desulfoferrodoxin using NADH/NADPH.

Abstract

Desulfoferrodoxin is a small protein found in sulfate-reducing bacteria that contains two independent mononuclear iron centers, one ferric and one ferrous. Expression of desulfoferrodoxin from Desulfoarculus baarsii has been reported to functionally complement a superoxide dismutase deficient Escherichia coli strain. To elucidate by which mechanism desulfoferrodoxin could substitute for superoxide dismutase in E. coli, we have purified the recombinant protein and studied its reactivity toward O-(2). Desulfoferrodoxin exhibited only a weak superoxide dismutase activity (20 units mg(-1)) that could hardly account for its antioxidant properties. UV-visible and electron paramagnetic resonance spectroscopy studies revealed that the ferrous center of desulfoferrodoxin could specifically and efficiently reduce O-(2), with a rate constant of 6-7 x 10(8) M(-1) s(-1). In addition, we showed that membrane and cytoplasmic E. coli protein extracts, using NADH and NADPH as electron donors, could reduce the O-(2) oxidized form of desulfoferrodoxin. Taken together, these results strongly suggest that desulfoferrodoxin behaves as a superoxide reductase enzyme and thus provide new insights into the biological mechanisms designed for protection from oxidative stresses.