Desulfoferrodoxin: a modular protein

. The gene encoding the non-heme iron-containing desulfoferrodoxin from Desulfovibrio vulgaris was cloned in two fragments in order to obtain polypeptides corresponding to the N- and C-terminal domains observed in the tertiary structure. These fragments were expressed in Escherichia coli , purified to homogeneity and biochemically and spectroscopically characterized. Both recombinant fragments behaved as independent metal-binding domains. The N-terminal fragment exhibited properties similar to desulforedoxin, as expected by the presence of a Fe(S-Cys) 4 metal binding motif. The C-terminal fragment, which accommodates a Fe(N ε -His) 3 (N δ -His)(S-Cys) center, was shown to have properties similar to neelaredoxin, except for the reaction with superoxide. The activities of desulfoferrodoxin and of the expressed C-terminal fragment were tested with superoxide in the presence and absence of cytochrome c . The results are consistent with superoxide reductase activity and a possible explanation for the low superoxide consumption in the superoxide dismutase activity assays is proposed.