Unlike superoxide dismutases (SODs), superoxide reductases (SORs) eliminate superoxide anion (O(2)(center dot-)) 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)(center dot-) with a pH-independent second-order rate constant k(1) =1.0 x 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. (C) 2011 Elsevier Inc. All rights reserved.
The superoxide reductase from the early diverging eukaryote Giardia intestinalis / Fabrizio, Testa; Mastronicola, Daniela; Diane E., Cabelli; Eugenio, Bordi; Leopoldo P., Pucillo; Sarti, Paolo; Lígia M., Saraiva; Giuffre', Alessandro; Miguel, Teixeira. - In: FREE RADICAL BIOLOGY & MEDICINE. - ISSN 0891-5849. - 51:8(2011), pp. 1567-1574. [10.1016/j.freeradbiomed.2011.07.017]
The superoxide reductase from the early diverging eukaryote Giardia intestinalis
MASTRONICOLA, Daniela;SARTI, Paolo;GIUFFRE', ALESSANDRO;
2011
Abstract
Unlike superoxide dismutases (SODs), superoxide reductases (SORs) eliminate superoxide anion (O(2)(center dot-)) 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)(center dot-) with a pH-independent second-order rate constant k(1) =1.0 x 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. (C) 2011 Elsevier Inc. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.