Ferredoxins amino acid sequence comparisons

Sequence comparisons may also suggest new ligands. Recently, the complete amino acid sequence for a ferredoxin from the thermophilic organism Pyrococcus furiosus was determined (Eccleston et al., 1991). All... 

The MoFe proteins isolated from all sources are 2/32 tetramers of Mr —220,000. The DNA sequences encoding the a subunit (nifD) and /3 subunit inifK) have been cloned and sequenced from seven organisms. The derived amino acid sequences indicate considerable homology, in particular live invariant Cys residues in the a subunit and three invariant Cys residues in the /3 subunit. As in the case with the Fe proteins, the conserved ferredoxin-like Cys-X-X-Cys spacing characteristic of many Fe-S proteins is not observed (Fig. 1). (25). Comparison of the sequences of the a and /3 subunits shows some homology, and X-ray... 

P. furiosus ferredoxin is a small protein of 66 amino acids (7500 Da) and is distinguished from most other ferredoxins by the coordination of its single [4Fe-4S] cluster by three, rather than four, cysteinyl residues. The fourth ligand is provided by an aspartyl residue. This is suggested by sequence comparisons with other 4Fe-type ferredoxins (Fig. 1). Their clusters are coordinated by a consensus sequence, Cys-X-X-Cys-X-X-Cys-(X) -Cys-Pro (where 35 residues). The P. furiosus protein is the notable exception as there is an Asp residue in place of the expected second Cys. Hence, the cluster in this ferredoxin is coordinated by... 

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