Abstract
Unlike superoxide dismutases (SODs), superoxide reductases (SORs) eliminate superoxide anion (O 2 •-) not through its dismutation, but via reduction to hydrogen peroxide (H 2O 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.
| Original language | English |
|---|---|
| Pages (from-to) | 1567-1574 |
| Number of pages | 8 |
| Journal | Free Radical Biology and Medicine |
| Volume | 51 |
| Issue number | 8 |
| DOIs | |
| Publication status | Published - Oct 15 2011 |
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Keywords
- Anaerobic protozoa
- Free radicals
- Nonheme iron protein
- Oxidative stress
- Superoxide detoxification
- Time-resolved spectroscopy
ASJC Scopus subject areas
- Biochemistry
- Physiology (medical)
Cite this
The superoxide reductase from the early diverging eukaryote Giardia intestinalis. / Testa, Fabrizio; Mastronicola, Daniela; Cabelli, Diane E.; Bordi, Eugenio; Pucillo, Leopoldo P.; Sarti, Paolo; Saraiva, Lígia M.; Giuffrè, Alessandro; Teixeira, Miguel.
In: Free Radical Biology and Medicine, Vol. 51, No. 8, 15.10.2011, p. 1567-1574.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The superoxide reductase from the early diverging eukaryote Giardia intestinalis
AU - Testa, Fabrizio
AU - Mastronicola, Daniela
AU - Cabelli, Diane E.
AU - Bordi, Eugenio
AU - Pucillo, Leopoldo P.
AU - Sarti, Paolo
AU - Saraiva, Lígia M.
AU - Giuffrè, Alessandro
AU - Teixeira, Miguel
PY - 2011/10/15
Y1 - 2011/10/15
N2 - Unlike superoxide dismutases (SODs), superoxide reductases (SORs) eliminate superoxide anion (O 2 •-) not through its dismutation, but via reduction to hydrogen peroxide (H 2O 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.
AB - Unlike superoxide dismutases (SODs), superoxide reductases (SORs) eliminate superoxide anion (O 2 •-) not through its dismutation, but via reduction to hydrogen peroxide (H 2O 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.
KW - Anaerobic protozoa
KW - Free radicals
KW - Nonheme iron protein
KW - Oxidative stress
KW - Superoxide detoxification
KW - Time-resolved spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=84860393559&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84860393559&partnerID=8YFLogxK
U2 - 10.1016/j.freeradbiomed.2011.07.017
DO - 10.1016/j.freeradbiomed.2011.07.017
M3 - Article
C2 - 21839165
AN - SCOPUS:84860393559
VL - 51
SP - 1567
EP - 1574
JO - Free Radical Biology and Medicine
JF - Free Radical Biology and Medicine
SN - 0891-5849
IS - 8
ER -