The crystal structure of superoxide dismutase from Plasmodium falciparum.

BACKGROUND: Superoxide dismutases (SODs) are important enzymes in defence against oxidative stress. In Plasmodium falciparum, they may be expected to have special significance since part of the parasite life cycle is spent in red blood cells where the formation of reactive oxygen species is likely to be promoted by the products of haemoglobin breakdown. Thus, inhibitors of P. falciparum SODs have potential as anti-malarial compounds. As a step towards their development we have determined the crystal structure of the parasite's cytosolic iron superoxide dismutase. RESULTS: The cytosolic iron superoxide dismutase from P. falciparum (PfFeSOD) has been overexpressed in E. coli in a catalytically active form. Its crystal structure has been solved by molecular replacement and refined against data extending to 2.5 A resolution. The structure reveals a two-domain organisation and an iron centre in which the metal is coordinated by three histidines, an aspartate and a solvent molecule. Consistent with ultracentrifugation analysis the enzyme is a dimer in which a hydrogen bonding lattice links the two active centres. CONCLUSION: The tertiary structure of PfFeSOD is very similar to those of a number of other iron-and manganese-dependent superoxide dismutases, moreover the active site residues are conserved suggesting a common mechanism of action. Comparison of the dimer interfaces of PfFeSOD with the human manganese-dependent superoxide dismutase reveals a number of differences, which may underpin the design of parasite-selective superoxide dismutase inhibitors.

Structures of two superoxide dismutases from Bacillus anthracis reveal a novel active centre.

The BA4499 and BA5696 genes of Bacillus anthracis encode proteins homologous to manganese superoxide dismutase, suggesting that this organism has an expanded repertoire of antioxidant proteins. Differences in metal specificity and quaternary structure between the dismutases of prokaryotes and higher eukaryotes may be exploited in the development of therapeutic antibacterial compounds. Here, the crystal structure of two Mn superoxide dismutases from B. anthracis solved to high resolution are reported. Comparison of their structures reveals that a highly conserved residue near the active centre is substituted in one of the proteins and that this is a characteristic feature of superoxide dismutases from the B. cereus/B. anthracis/B. thuringiensis group of organisms.

Structural and biochemical characterization of a mitochondrial peroxiredoxin from Plasmodium falciparum.

Plasmodium falciparum possesses a single mitochondrion with a functional electron transport chain. During respiration, reactive oxygen species are generated that need to be removed to protect the organelle from oxidative damage. In the absence of catalase and glutathione peroxidase, the parasites rely primarily on peroxiredoxin-linked systems for protection. We have analysed the biochemical and structural features of the mitochondrial peroxiredoxin and thioredoxin of P. falciparum. The mitochondrial localization of both proteins was confirmed by expressing green fluorescent protein fusions in parasite erythrocytic stages. Recombinant protein was kinetically characterized using the cytosolic and the mitochondrial thioredoxin (PfTrx1 and PfTrx2 respectively). The peroxiredoxin clearly preferred PfTrx2 to PfTrx1 as a reducing partner, reflected by the KM values of 11.6 microM and 130.4 microM respectively. Substitution of the two dyads asparagine-62/tyrosine-63 and phenylalanine-139/alanine-140 residues by aspartate-phenylalaine and valine-serine, respectively, reduced the KM for Trx1 but had no effect on the KM of Trx2 suggesting some role for these residues in the discrimination between the two substrates. Solution studies suggest that the protein exists primarily in a homodecameric form. The crystal structure of the mitochondrial peroxiredoxin reveals a fold typical of the 2-Cys class peroxiredoxins and a dimeric form with an intermolecular disulphide bridge between Cys67 and Cys187. These results show that the mitochondrial peroxiredoxin of P. falciparum occurs in both dimeric and decameric forms when purified under non-reducing conditions.