The superoxide reductase from the early diverging eukaryote Giardia intestinalis.

Fabrizio Testa (1, 2) , Daniela Mastronicola (1, 2) , Diane E Cabelli (3) , Eugenio Bordi (4) , Leopoldo P Pucillo (4) , Paolo Sarti (1, 2) , Lígia M Saraiva (5) , Alessandro Giuffrè (1, 2) , Miguel Teixeira (5)

1 Department of Biochemical Sciences "Rossi Fanelli"
2 CNR - National Research Council of Italy -
3 Chemistry Department, Brookhaven National Laboratory
4 L. Spallanzani National Institute for Infectious Diseases
5 ITQB - Instituto de Tecnologia Química e Biológica António Xavier

Unlike superoxide dismutases (SODs), superoxide reductases (SORs) eliminate superoxide anion (O(2)(*-)) not through its dismutation, but via reduction to hydrogen peroxide (H(2)O(2)) in the presence of an electron donor. The microaerobic protist Giardia intestinalis, responsible for a common intestinal disease in humans, though lacking SOD and other canonical reactive oxygen species-detoxifying systems, is among the very few eukaryotes encoding a SOR yet identified. In this study, the recombinant SOR from Giardia (SOR(Gi)) was purified and characterized by pulse radiolysis and stopped-flow spectrophotometry. The protein, isolated in the reduced state, after oxidation by superoxide or hexachloroiridate(IV), yields a resting species (T(final)) with Fe(3+) ligated to glutamate or hydroxide depending on pH (apparent pK(a)=8.7). Although showing negligible SOD activity, reduced SOR(Gi) reacts with O(2)(*-) with a pH-independent second-order rate constant k(1)=1.0×10(9) M(-1) s(-1) and yields the ferric-(hydro)peroxo intermediate T(1); this in turn rapidly decays to the T(final) state with pH-dependent rates, without populating other detectable intermediates. Immunoblotting assays show that SOR(Gi) is expressed in the disease-causing trophozoite of Giardia. We propose that the superoxide-scavenging activity of SOR in Giardia may promote the survival of this air-sensitive parasite in the fairly aerobic proximal human small intestine during infection.

Domains: Biochemistry, Molecular Biology

Fabrizio Testa, Daniela Mastronicola, Diane E Cabelli, Eugenio Bordi, Leopoldo P Pucillo, et al.. The superoxide reductase from the early diverging eukaryote Giardia intestinalis.. Free Radical Biology and Medicine, 2011, 51 (8), pp.1567-74. ⟨10.1016/j.freeradbiomed.2011.07.017⟩. ⟨pasteur-00976043⟩