Recent studies have shown that the ferric uptake regulator (Fur) of
Edwardsiella tarda (Fur
Et) shares high sequence identity with the
Escherichia coli Fur (Fur
Ec) at the N-terminal DNA-binding region. In the present study, the functional importance of the C-terminal region of Fur
Et was investigated. It was found that Fur
Et bearing deletion of the C-terminal 12 residues still possesses most of the repressor activity, whereas Fur
Et bearing deletions of the C-terminal 16 and more than 16 residues are severely affected in activity. Domain swapping analyses indicated that the chimeric Fur proteins (Et75Ec73 and Et75Vh74) consisting of the N-terminal 1-75 region of Fur
Et fused to the C-terminal 76-148 region of Fur
Ec and the C-terminal 76-149 region of the
Vibrio harveyi Fur (Fur
Vh), respectively, are fully active. C92 of Fur
Ec and C137 of Fur
Vh, which are functionally essential in Fur
Ec and Fur
Vh, respectively, are also essential in Et75Ec73 and Et75Vh74, respectively. Further study identified an artificial Fur protein, EtMF54, which is composed of the N-terminal 49 residues of Fur
Et and five artificial residues. Compared to Fur
Et, EtMF54 possesses partial Fur activity that is iron-dependent. These results (i) indicate that there exist certain functional/structural compatibilities among Fur
Et, Fur
Ec, and Fur
Vh at the C-terminal region; (ii) provide insights to the potential location of the regulatory ion-binding site of Fur
Et.
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