1e0z
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[2FE-2S]-FERREDOXIN FROM HALOBACTERIUM SALINARUM
OverviewOverview
The [2Fe-2S] ferredoxin (HsFdx) of the halophilic archaeon Halobacterium, salinarum exhibits a high degree of sequence conservation with plant-type, ferredoxins except for an insertion of 30 amino acids near its N-terminus, which is extremely rich in acidic amino acids. Unfolding studies reveal, that HsFdx has an unfolding temperature of approximately 85 degrees C in, 4.3 M NaCl, but of only 50 degrees C in low salinity, revealing its, halophilic character. The three-dimensional structure of HsFdx was, determined by NMR spectroscopy, resulting in a backbone rmsd of 0.6 A for, the diamagnetic regions of the protein. Whereas the overall structure of, HsFdx is very similar to that of the plant-type ferredoxins, two, additional alpha-helices are found in the acidic extra domain. (15)N NMR, relaxation studies indicate that HsFdx is rigid, and the flexibility of, residues is similar throughout the molecule. Monitoring protein, denaturation by NMR did not reveal differences between the core fold and, the acidic domain, suggesting a cooperative unfolding of both parts of the, molecule. A mutant of the HsFdx in which the acidic domain is replaced, with a short loop of the nonhalophilic Anabaena ferredoxin shows a, considerably changed expression pattern. The halophilic wild-type protein, is readily expressed in large amounts in H. salinarum, but not in, Escherichia coli, whereas the mutant ferredoxin could only be, overexpressed in E. coli. The salt concentration was also found to play a, critical role for the efficiency of cluster reconstitution: the cluster of, HsFdx could be reconstituted only in a solution containing molar, concentrations of NaCl, while the reconstitution of the cluster in the, mutant protein proceeds efficiently in low salt. These findings suggest, that the acidic domain mediates the halophilic character which is, reflected in its thermostability, the exclusive expression in H., salinarum, and the ability to efficiently reconstitute the iron-sulfur, cluster only at high salt concentrations.
About this StructureAbout this Structure
1E0Z is a Single protein structure of sequence from Halobacterium salinarum with ACE and FES as ligands. Full crystallographic information is available from OCA.
ReferenceReference
A two-alpha-helix extra domain mediates the halophilic character of a plant-type ferredoxin from halophilic archaea., Marg BL, Schweimer K, Sticht H, Oesterhelt D, Biochemistry. 2005 Jan 11;44(1):29-39. PMID:15628843
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