Oxygen detoxification in the strict anaerobic archaeon Archaeoglobus fulgidus: superoxide scavenging by neelaredoxin.
Archaeoglobus fulgidus is a hyperthermophilic sulphate-reducing archaeon. It has an optimum growth temperature of 83 degrees C and is described as a strict anaerobe. Its genome lacks any homologue of canonical superoxide (O2.-) dismutases. In this work, we show that neelaredoxin (Nlr) is the main O2.- scavenger in A. fulgidus, by studying both the wild-type and recombinant proteins. Nlr is a 125-amino-acid blue-coloured protein containing a single iron atom/molecule, which in the oxidized state is high spin ferric. This iron centre has a reduction potential of +230 mV at pH 7.0. Nitroblue tetrazolium-stained gel assays of cell-soluble extracts show that Nlr is the main protein from A. fulgidus which is reactive towards O2.-. Furthermore, it is shown that Nlr is able to both reduce and dismutate O2.-, thus having a bifunctional reactivity towards O2.-. Kinetic and spectroscopic studies indicate that Nlr's superoxide reductase activity may allow the cell to eliminate O2.- quickly in a NAD(P)H-dependent pathway. On the other hand, Nlr's superoxide dismutation activity will allow the cell to detoxify O2.- independently of the cell redox status. Its superoxide dismutase activity was estimated to be 59 U mg-1 by the xanthine/xanthine oxidase assay at 25 degrees C. Pulse radiolysis studies with the isolated and reduced Nlr proved unambiguously that it has superoxide dismutase activity; at pH 7.1 and 83 degrees C, the rate constant is 5 x 106 M-1 s-1. Besides the superoxide dismutase activity, soluble cell extracts of A. fulgidus also exhibit catalase and NAD(P)H/oxygen oxidoreductase activities. By putting these findings together with the entire genomic data available, a possible oxygen detoxification mechanism in A. fulgidus is discussed.
Abreu
I A
IA
Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Rua da Quinta Grande 6, 2780-156 Oeiras, Portugal.
Saraiva
L M
LM
Carita
J
J
Huber
H
H
Stetter
K O
KO
Cabelli
D
D
Teixeira
M
M
D000595:Amino Acid Sequence; D000693:Anaerobiosis; D019611:Archaeoglobus fulgidus / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004579:Electron Transport; D016166:Free Radical Scavengers / Q000145:classification / Q000302:isolation & purification / Q000378:metabolism*; D033862:Iron-Binding Proteins; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010100:Oxygen; D017386:Sequence Homology, Amino Acid; D013482:Superoxide Dismutase / Q000145:classification / Q000302:isolation & purification / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*
D001426:Bacterial Proteins; D002352:Carrier Proteins; D016166:Free Radical Scavengers; D033862:Iron-Binding Proteins; D013481:Superoxides; D010088:Oxidoreductases; C121849:superoxide reductase; D013482:Superoxide Dismutase; C414179:nlr protein, Desulfovibrio gigas; D010100:Oxygen