Diversity of chemical mechanisms in thioredoxin catalysis revealed by single-molecule force spectroscopy.

Thioredoxins (Trxs) are oxidoreductase enzymes, present in all organisms, that catalyze the reduction of disulfide bonds in proteins. By applying a calibrated force to a substrate disulfide, the chemical mechanisms of Trx catalysis can be examined in detail at the single-molecule level. Here we use single-molecule force-clamp spectroscopy to explore the chemical evolution of Trx catalysis by probing the chemistry of eight different Trx enzymes.

Chloroplast monothiol glutaredoxins as scaffold proteins for the assembly and delivery of [2Fe-2S] clusters.

Glutaredoxins (Grxs) are small oxidoreductases that reduce disulphide bonds or protein-glutathione mixed disulphides. More than 30 distinct grx genes are expressed in higher plants, but little is currently known concerning their functional diversity. This study presents biochemical and spectroscopic evidence for incorporation of a [2Fe-2S] cluster in two heterologously expressed chloroplastic Grxs, GrxS14 and GrxS16, and in vitro cysteine desulphurase-mediated assembly of an identical [2Fe-2S] cluster in apo-GrxS14.

Active site mutagenesis and phospholipid hydroperoxide reductase activity of poplar type II peroxiredoxin.

The nature of the active site and the substrate specificity of poplar type II peroxiredoxin, an enzyme which preferentially uses glutaredoxin as an electron donor, were investigated in this study. The type II peroxiredoxin is able to use phospholipid hydroperoxide nearly as efficiently as hydrogen peroxide. Two of the hyper-conserved amino acid residues in peroxiredoxins have been altered, by site-directed mutagenesis, generating the mutants T48V and R129Q.

Evidence for a subgroup of thioredoxin h that requires GSH/Grx for its reduction.

Poplar thioredoxin h4 (popTrxh4) and a related CXXS type (popCXXS3) are both members of a plant thioredoxin h subgroup. PopTrxh4 exhibits the usual catalytic site WCGPC, whereas popCXXS3 harbors the non-typical active site WCMPS. Recombinant popTrxh4 and popCXXS3 are not reduced either by Arabidopsis thaliana NADPH-dependent thioredoxin reductases (NTR) A and B or by Escherichia coli NTR.

Molecular and catalytic properties of a peroxiredoxin-glutaredoxin hybrid from Neisseria meningitidis.

A hybrid protein from Neisseria meningitidis, which contains both a peroxiredoxin and a glutaredoxin domain, has been isolated. The enzyme was active in the reduction of various peroxides and dehydroascorbate in the presence of reduced glutathione. These findings suggest that both the peroxiredoxin and glutaredoxin domains are biochemically active in the fusion.

Crystallization and preliminary X-ray data of a bifunctional peroxiredoxin from poplar.

Two variants (wild type and V152C mutant) of a bifunctional poplar peroxiredoxin have been overexpressed in Escherichia coli cells. The two recombinant enzymes were purified and crystallized using the hanging-drop vapour-diffusion technique. Data sets were collected to 1.

Glutaredoxin-dependent peroxiredoxin from poplar: protein-protein interaction and catalytic mechanism.

Recently, a poplar phloem peroxiredoxin (Prx) was found to accept both glutaredoxin (Grx) and thioredoxin (Trx) as proton donors. To investigate the catalytic mechanism of the Grx-dependent reduction of hydroperoxides catalyzed by Prx, a series of cysteinic mutants was constructed. Mutation of the most N-terminal conserved cysteine of Prx (Cys-51) demonstrates that it is the catalytic one.