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“Background Ferredoxin (Fdx) is the name given to a variety of small proteins binding inorganic clusters organized around two to four iron atoms and a complementary number of sulfur atoms . Complete genomic sequences have revealed the presence of a very large number of genes encoding such proteins, mainly in bacteria and archaea . Fdxs are most often assigned selleck inhibitor electron transfer roles and some of them occupy central positions in metabolism , but the roles of a majority of Fdxs remain unknown [4, 5]. Functional substitution among Fdxs may occur, and other soluble electron shuttles, such as flavodoxins,
may act as Fdx-substitutes. This is the case upon iron starvation for a 2[4Fe-4S] Fdx in glycolytic Clostridia  or a [2Fe-2S] Fdx in some photosynthetic organisms , for instance. Despite this apparent functional redundancy, most sequenced genomes display a wealth of genes Liothyronine Sodium encoding various Fdxs. For example, the reference PAO1 strain of the opportunistic pathogen Pseudomonas aeruginosa  has at least 6 genes encoding Fdxs of different families. A flavodoxin (PA3435) is also present in this strain. It is often unclear in which reactions Fdxs are involved and which biological function relies on a given Fdx. One of P. aeruginosa Fdxs is encoded by the PA0362 locus (fdx1) and it belongs to a separated family of proteins containing two [4Fe-4S] clusters . The sequences of proteins of this family are characterized by a segment of six amino acids between two cysteine ligands of one cluster and a C terminal extension of more than 20 amino acids beyond the last ligand of the other cluster (Figure 1).