A hyperthermophilic plant-type [2Fe-2S] ferredoxin from Aquifex aeolicus is stabilized by a disulfide bond.

A [2Fe-2S] ferredoxin (Fd1) from the hyperthermophilic bacterium Aquifex aeolicus has been obtained by heterologous expression of the encoding gene in Escherichia coli. Sequence comparisons show that this protein belongs to the extended family of plant- and mammalian-type [2Fe-2S] ferredoxins but also indicate that it is not closely similar to either the plant-type or mammalian-type subfamilies. Instead, it appears to bear some similarity to novel members of this family, in particular the Isc-type ferredoxins involved in the assembly of iron−sulfur clusters in vivo. The two redox levels of the [2Fe-2S]2+/+ metal site of A. aeolicus ferredoxin have been studied by UV−visible, resonance Raman, EPR, variable temperature magnetic circular dichroism, and Mossbauer spectroscopies. A full-spin Hamiltonian analysis is given for the Mossbauer spectra. In aggregate, the spectroscopic data reveal differences with both the plant-type and mammalian-type ferredoxins, in keeping with the sequence comparisons. The midpoi...