The Superoxide Reductase from the Early Diverging Eukaryote Giardia Intestinalis

Journal Article · Sat Oct 15 04:00:00 EDT 2011 · Free Radical Biology and Medicine

OSTI ID:1040547

Cabelli, D E; Testa, F; Mastronicola, D; Bordi, E; Pucillo, L P; Sarti, P; Saraiva, L M; Giuffre, A; Teixeira, M

Unlike superoxide dismutases (SODs), superoxidereductases (SORs) eliminate superoxide anion (O{sub 2}{sup {sm_bullet}-}) not through its dismutation, but via reduction to hydrogen peroxide (H{sub 2}O{sub 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{sub 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{sub final}) with Fe{sup 3+} ligated to glutamate or hydroxide depending on pH (apparent pK{sub a} = 8.7). Although showing negligible SOD activity, reduced SOR{sub Gi} reacts with O{sub 2}{sup {sm_bullet}-} with a pH-independent second-order rate constant k{sub 1} = 1.0 x 10{sup 9} M{sup -1} s{sup -1} and yields the ferric-(hydro)peroxo intermediate T{sub 1}; this in turn rapidly decays to the T{sub final} state with pH-dependent rates, without populating other detectable intermediates. Immunoblotting assays show that SOR{sub 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.

• Research Organization: BROOKHAVEN NATIONAL LABORATORY (BNL)
• Sponsoring Organization: USDOE SC OFFICE OF SCIENCE (SC)
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 1040547
• Report Number(s): BNL--94884-2011-JA
• Journal Information: Free Radical Biology and Medicine, Journal Name: Free Radical Biology and Medicine Journal Issue: 8 Vol. 51; ISSN 0891-5849; ISSN FRBMEH
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
ANIONS
BINDING ENERGY
DISEASES
ELECTRONS
HYDROGEN PEROXIDE
HYDROXIDES
OXIDATION
OXIDOREDUCTASES
OXYGEN
PARASITES
RADIOLYSIS
SMALL INTESTINE
SPECTROPHOTOMETRY
SUPEROXIDE DISMUTASE
VALENCE
pulse radiolysis
superoxide