1zcp
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Crystal Structure of a catalytic site mutant E. coli TrxA (CACA)
OverviewOverview
Escherichia coli thioredoxin is a small monomeric protein that reduces, disulfide bonds in cytoplasmic proteins. Two cysteine residues present in, a conserved CGPC motif are essential for this activity. Recently, we, identified mutations of this motif that changed thioredoxin into a, homodimer bridged by a [2Fe-2S] iron-sulfur cluster. When exported to the, periplasm, these thioredoxin mutants could restore disulfide bond, formation in strains lacking the entire periplasmic oxidative pathway., Essential for the assembly of the iron-sulfur was an additional cysteine, that replaced the proline at position three of the CGPC motif. We solved, the crystalline structure at 2.3 Angstroms for one of these variants, TrxA(CACA). The mutant protein crystallized as a dimer in which the, iron-sulfur cluster is replaced by two intermolecular disulfide bonds. The, catalytic site, which forms the dimer interface, crystallized in two, different conformations. In one of them, the replacement of the CGPC motif, by CACA has a dramatic effect on the structure and causes the unraveling, of an extended alpha-helix. In both conformations, the second cysteine, residue of the CACA motif is surface-exposed, which contrasts with, wildtype thioredoxin where the second cysteine of the CXXC motif is, buried. This exposure of a pair of vicinal cysteine residues apparently, allows thioredoxin to acquire an iron-sulfur cofactor at its active site, and thus a new activity and mechanism of action.
About this StructureAbout this Structure
1ZCP is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
ReferenceReference
The crystal structure of TrxA(CACA): Insights into the formation of a [2Fe-2S] iron-sulfur cluster in an Escherichia coli thioredoxin mutant., Collet JF, Peisach D, Bardwell JC, Xu Z, Protein Sci. 2005 Jul;14(7):1863-9. PMID:15987909
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