Role of the
            <i>Azotobacter vinelandii</i>
            Nitrogenase-Protective Shethna Protein in Preventing Oxygen-Mediated Cell Death

Maier, Robert J.; Moshiri, Farhad

doi:10.1128/jb.182.13.3854-3857.2000

Cited by 41 publications

(31 citation statements)

References 17 publications

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“…This suggests that high turnover rates of nitrogenase provide active enzyme complexes for N 2 fixation despite the presence of higher intracellular O 2 levels. It is notable that FeS proteins play an important role in Azotobacter vinelandii, possibly by forming a complex with nitrogenase to generate an inactive but oxygen-stable enzyme complex (28,29,49) This process is termed conformational protection, but we could not identify a similar protein in Cyanothece; however, we VOL. 190, 2008 EFFECT OF CONTINUOUS LIGHT ON CYANOTHECE TRANSCRIPTION 3911…”

Section: Discussionmentioning

confidence: 71%

Differential Transcriptional Analysis of the Cyanobacterium Cyanothece sp. Strain ATCC 51142 during Light-Dark and Continuous-Light Growth

et al. 2008

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We analyzed the metabolic rhythms and differential gene expression in the unicellular, diazotrophic cyanobacterium Cyanothece sp. strain ATCC 51142 under N 2 -fixing conditions after a shift from normal 12-h light-12-h dark cycles to continuous light. We found that the mRNA levels of ϳ10% of the genes in the genome demonstrated circadian behavior during growth in free-running (continuous light) conditions. The genes for N 2 fixation displayed a strong circadian behavior, whereas photosynthesis and respiration genes were not as tightly regulated. One of our main objectives was to determine the strategies used by these cells to perform N 2 fixation under normal day-night conditions, as well as under the greater stress caused by continuous light. We determined that N 2 fixation cycled in continuous light but with a lower N 2 fixation activity. Glycogen degradation, respiration, and photosynthesis were also lower; nonetheless, O 2 evolution was about 50% of the normal peak. We also demonstrated that nifH (encoding the nitrogenase Fe protein), nifB, and nifX were strongly induced in continuous light; this is consistent with the role of these proteins during the assembly of the enzyme complex and suggested that the decreased N 2 fixation activity was due to protein-level regulation or inhibition. Many soluble electron carriers (e.g., ferredoxins), as well as redox carriers (e.g., thioredoxin and glutathione), were strongly induced during N 2 fixation in continuous light. We suggest that these carriers are required to enhance cyclic electron transport and phosphorylation for energy production and to maintain appropriate redox levels in the presence of elevated O 2 , respectively.

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Section: Discussionmentioning

confidence: 71%

Differential Transcriptional Analysis of the Cyanobacterium Cyanothece sp. Strain ATCC 51142 during Light-Dark and Continuous-Light Growth

et al. 2008

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“…The iron-sulfur clusters of Azotobacter vinelandii nitrogenase are thought to be shielded during periods of oxygen exposure by Shethna protein (39). In this situation, however, the protected nitrogenase is catalytically inactive, regaining function only when low oxygen levels are restored and the Shethna protein is deactivated.…”

Section: Discussionmentioning

confidence: 99%

Contrasting Sensitivities of Escherichia coli Aconitases A and B to Oxidation and Iron Depletion

2003

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Superoxide damages dehydratases that contain catalytic [4Fe-4S]2؉ clusters. Aconitases are members of that enzyme family, and previous work showed that most aconitase activity is lost when Escherichia coli is exposed to superoxide stress. More recently it was determined that E. coli synthesizes at least two isozymes of aconitase, AcnA and AcnB. Synthesis of AcnA, the less-abundant enzyme, is positively controlled by SoxS, a protein that is activated in the presence of superoxide-generating chemicals. We have determined that this arrangement exists because AcnA is resistant to superoxide in vivo. Surprisingly, purified AcnA is extremely sensitive to superoxide and other chemical oxidants unless it is combined with an uncharacterized factor that is present in cell extracts. In contrast, AcnB is highly sensitive to a variety of chemical oxidants in vivo, in extracts, and in its purified form. Thus, the induction of AcnA during oxidative stress provides a mechanism to circumvent a block in the tricarboxylic acid cycle. AcnA appears to be as catalytically competent as AcnB, so the retention of the latter as the primary housekeeping enzyme must provide some other advantage. We observed that the [4Fe-4S] cluster of AcnB is in dynamic equilibrium with the surrounding iron pool, so that AcnB is rapidly demetallated when intracellular iron pools drop. AcnA and other dehydratases do not show this trait. Demetallated AcnB is known to bind its cognate mRNA. The absence of AcnB activity also causes the accumulation and excretion of citrate, an iron chelator for which E. coli synthesizes a transport system. Thus, AcnB may be retained as the primary aconitase because the lability of its exposed cluster allows E. coli to sense and respond to iron depletion.

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“…In this complex, nitrogenase is inactive but transiently protected from damage by oxygen (10,13,21). Additional studies have shown that the function of the FeSII protein is of major importance for cell viability under carbon and/or energy limitation but only when cells are grown diazotrophically (12,14).…”

mentioning

confidence: 99%

Evidence for Conformational Protection of Nitrogenase against Oxygen in Gluconacetobacter diazotrophicus by a Putative FeSII Protein

Ureta

Nordlund

2002

J Bacteriol

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Role of the Azotobacter vinelandii Nitrogenase-Protective Shethna Protein in Preventing Oxygen-Mediated Cell Death

Cited by 41 publications

References 17 publications

Differential Transcriptional Analysis of the Cyanobacterium Cyanothece sp. Strain ATCC 51142 during Light-Dark and Continuous-Light Growth

Differential Transcriptional Analysis of the Cyanobacterium Cyanothece sp. Strain ATCC 51142 during Light-Dark and Continuous-Light Growth

Contrasting Sensitivities of Escherichia coli Aconitases A and B to Oxidation and Iron Depletion

Evidence for Conformational Protection of Nitrogenase against Oxygen in Gluconacetobacter diazotrophicus by a Putative FeSII Protein

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