Domain analysis of the Edwardsiella tarda ferric uptake regulator

Abstract

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.