Structural comparison of the ferredoxin domains: Structural diagrams of (a) CheY-binding domain of CheA that belongs to the α+β ferredoxin-like fold (PDB: 1ffg, chain B) and (b) leghemoglobin (PDB: 2 gdm, chain A) that belongs to the globin-like fold. The structures of (c) bacterial ferredoxin domain that adopts the α+β ferredoxin-like fold and (d) α-helical ferredoxin that adopts the globin-like fold are shown. The Cα atoms of the cysteine residues that ligate [4Fe-4S] ([3Fe-4S]) clusters are shown in CPK (yellow). The loops and helices that contribute to cluster-binding are colored red (loops) and cyan (helices), respectively. Other elements are colored grey. (e) Stereo diagram of the structural superposition of a bacterial ferredoxin (1feh, red)  with a α-helical ferredoxin (1kf6, black). The structures were superimposed using the program insightII by manually defining equivalent residue pairs, which are shown as thick lines (1feh, chain A: 145–157, 188–205; 1kf6, chain B: 146–158, 202–219; RMSD 0.98 Å). All figures were made using the program BOBSCRIPT .