期刊
FREE RADICAL BIOLOGY AND MEDICINE
卷 51, 期 8, 页码 1567-1574出版社
ELSEVIER SCIENCE INC
DOI: 10.1016/j.freeradbiomed.2011.07.017
关键词
Oxidative stress; Anaerobic protozoa; Nonheme iron protein; Superoxide detoxification; Time-resolved spectroscopy; Free radicals
资金
- Ministero dell'Istruzione, dell'Universita e della Ricerca, Italy [FIRB RBFR08F41U_001, PRIN 2008FJJHKM_002]
- European Society of Clinical Microbiology and Infectious Diseases
- Fundacao para a Ciencia e Tecnologia, Portugal [PTDC/BIA-Pro/6726372006]
- Consiglio Nazionale delle Ricerche of Italy
- Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy [DE-AC02-98-CH10886]
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.
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