The genetic organization of Desulfovibrio desulphuricans ATCC 27774 bacterioferritin and rubredoxin-2 genes: involvement of rubredoxin in iron metabolism

The anaerobic bacterium Desulfovibrio desulphuricans ATCC 27774 contains a unique bacterioferritin, isolated with a stable di-iron centre and having i ron-coproporphyrin III as its haem cofactor, as well as a type 2 rubredoxin with an unusual spacing of four amino acid residues between the first two binding cysteines. The genes encoding for these two proteins were cloned an d sequenced. The deduced amino acid sequence of the bacterioferritin shows that it is among the most divergent members of this protein family. Most in terestingly, the bacterioferritin and rubredoxin-a genes form a dicistronic operon, which reflects the direct interaction between the two proteins. In deed, bacterioferritin and rubredoxin-2 form a complex in vitro, as shown b y the significant increase in the anisotropy and decay times of the fluores cence of rubredoxin-2 tryptophan(s) when mixed with bacterioferritin. In ad dition, rubredoxin-2 donates electrons to bacterioferritin. This is the fir st identification of an electron donor to a bacterioferritin and shows the involvement of rubredoxin-2 in iron metabolism. Furthermore, analysis of th e genomic data for anaerobes suggests that rubredoxins play a general role in iron metabolism and oxygen detoxification In these prokaryotes.