Structure of a thioredoxin-like [2Fe-2S] ferredoxin from Aquifex aeolicus

The 2.3 Angstrom resolution crystal structure of a [2Fe-2S] cluster contain ing ferredoxin from Aquifex aeolicus reveals a thioredoxin-like fold that i s novel among iron-sulfur proteins. The [2Fe-2S] cluster is located near th e surface of the protein, at a site corresponding to that of the active-sit e disulfide bridge in thioredoxin. The four cysteine ligands are located ne ar the ends of two surface loops. Two of these ligands can be substituted b y non-native cysteine residues introduced throughout a stretch of the polyp eptide chain that forms a protruding loop extending away from the cluster. The presence of homologs of this ferredoxin as components of more complex a naerobic and aerobic electron transfer systems indicates that this is a ver satile fold for biological redox processes. (C) 2000 Academic Press.