Desulfoferrodoxin: a modular protein

The gene encoding the non-heme iron-containing desulfoferrodoxin from Desul fovibrio vulgaris was cloned in two fragments in order to obtain polypeptid es 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 rec ombinant fragments behaved as independent metal-binding domains. The N-term inal fragment exhibited properties similar to desulforedoxin, as expected b y the presence of a Fe(S-Cys)(4) metal binding motif, The C-terminal fragme nt, which accommodates a Fe(N-epsilon-His)(3)(N-delta-His)(S-Cys) center, w as shown to have properties similar to neelaredoxin, except for the reactio n with superoxide. The activities of desulfoferrodoxin and of the expressed C-terminal fragment were tested with superoxide in the presence and absenc e of cytochrome c, The results are consistent with superoxide reductase act ivity and a possible explanation for the low superoxide consumption in the superoxide dismutase activity assays is proposed.