In:
Applied and Environmental Microbiology, American Society for Microbiology, Vol. 75, No. 4 ( 2009-02-15), p. 1021-1029
Abstract:
Clostridium acetobutylicum , an obligate anaerobe, grows normally under continuous-O 2 -flow culture conditions, where the cells consume O 2 proficiently. An O 2 -responsive NADH:rubredoxin oxidoreductase operon composed of three genes ( nror , fprA2 , and dsr ), encoding NROR, functionally uncharacterized flavoprotein A2 (FprA2), and the predicted superoxide reductase desulfoferrodoxin (Dsr), has been proposed to participate in defense against O 2 stress. To functionally characterize these proteins, native NROR from C. acetobutylicum , recombinant NROR (rNROR), FprA2, Dsr, and rubredoxin (Rd) expressed in Escherichia coli were purified. Purified native NROR and rNROR both exhibited weak H 2 O 2 -forming NADH oxidase activity that was slightly activated by Rd. A mixture of NROR, Rd, and FprA2 functions as an efficient H 2 O-forming NADH oxidase with a high affinity for O 2 (the K m for O 2 is 2.9 ± 0.4 μM). A mixture of NROR, Rd, and Dsr functions as an NADH-dependent O 2 − reductase. A mixture of NROR, Rd, and rubperoxin (Rpr, a rubrerythrin homologue) functions as an inefficient H 2 O-forming NADH oxidase but an efficient NADH peroxidase with a low affinity for O 2 and a high affinity for H 2 O 2 (the K m s for O 2 and H 2 O 2 are 303 ± 39 μM and ≤1 μM, respectively). A gene encoding Rd is dicistronically transcribed with a gene encoding a glutaredoxin (Gd) homologue, and the expression levels of the genes encoding Gd and Rd were highly upregulated upon exposure to O 2 . Therefore, nror operon enzymes, together with Rpr, efficiently function to scavenge O 2 , O 2 − , and H 2 O 2 by using an O 2 -responsive rubredoxin as a common electron carrier protein.
Type of Medium:
Online Resource
ISSN:
0099-2240
,
1098-5336
DOI:
10.1128/AEM.01425-08
Language:
English
Publisher:
American Society for Microbiology
Publication Date:
2009
detail.hit.zdb_id:
223011-2
detail.hit.zdb_id:
1478346-0
SSG:
12
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