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PDBsum entry 3f8d
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Oxidoreductase
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PDB id
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3f8d
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References listed in PDB file
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Key reference
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Title
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Structure and stability of a thioredoxin reductase from sulfolobus solfataricus: a thermostable protein with two functions.
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Authors
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A.Ruggiero,
M.Masullo,
M.R.Ruocco,
P.Grimaldi,
M.A.Lanzotti,
P.Arcari,
A.Zagari,
L.Vitagliano.
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Ref.
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Biochim Biophys Acta, 2009,
1794,
554-562.
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PubMed id
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Abstract
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Recent investigations have demonstrated that disulfide bridges may play a
crucial role in the stabilization of proteins in hyperthermophilic organisms. A
major role in the process of disulfide formation is played by ubiquitous
proteins belonging to the thioredoxin superfamily, which includes thioredoxins
(Trx), thioredoxin reductases (TrxR), and disulfide oxidases/isomerases
(PDO/PDI). Here we report a characterization of the structure and stability of
the TrxR (SsTrxRB3) isolated from the archaeon Sulfolobus solfataricus. This
protein is particularly interesting since it is able to process different
substrates (Trxs and PDO) and it is endowed with an additional NADH oxidase
activity. The crystal structure of the wild-type enzyme, of its complex with
NADP and of the C147A mutant provides interesting clues on the enzyme function.
In contrast to what is observed for class II TrxRs, in the structure of the
oxidized enzyme, the FAD binding site is occupied by a partially disordered NAD
molecule. In the active site of the C147A mutant, which exhibits a marginal NADH
oxidase activity, the FAD is canonically bound to the enzyme. Molecular modeling
indicates that a FAD molecule can be accommodated in the site of the reduced
SsTrxRB3. Depending on the oxidation state, SsTrxRB3 can bind a different
cofactor in its active site. This peculiar feature has been related to its dual
activity. Denaturation experiments followed by circular dichroism indicate that
electrostatic interactions play an important role in the stabilization of this
thermostable protein. The analysis of the enzyme 3D-structure has also provided
insights into the bases of SsTrxRB3 stability.
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