Vanadium nitrogenase: A two-hit wonder?

Hu, Yilin; Lee, Chi Chung; Ribbe, Markus W.

doi:10.1039/c1dt11535a

Cited by 121 publications

(127 citation statements)

References 53 publications

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“…CO tolerance of Fe-nitrogenase against up to 1% CO may result from CO reduction by the alternative nitrogenase. It is worth noting that V-nitrogenase exhibits much higher CO-reducing activity than Mo-nitrogenase (15,16). Thus, CO reduction activity might be a general feature of alternative nitrogenases.…”

Section: Discussionmentioning

confidence: 99%

“…Even Mo-nitrogenase produces CO by reduction of CO 2 , albeit at low rates (13,14). On the other hand, CO is a substrate for Mo-nitrogenase, but its CO-reducing activity is very low (15). In contrast, CO is a much better substrate for V-nitrogenase (15,16).…”

mentioning

confidence: 96%

“…On the other hand, CO is a substrate for Mo-nitrogenase, but its CO-reducing activity is very low (15). In contrast, CO is a much better substrate for V-nitrogenase (15,16). To date, it is unknown to what extent, if at all, Fe-nitrogenase is able to reduce CO.…”

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confidence: 96%

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NifA- and CooA-Coordinated cowN Expression Sustains Nitrogen Fixation by Rhodobacter capsulatus in the Presence of Carbon Monoxide

et al. 2014

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Rhodobacter capsulatus fixes atmospheric dinitrogen via two nitrogenases, Mo-and Fe-nitrogenase, which operate under different conditions. Here, we describe the functions in nitrogen fixation and regulation of the rcc00574 (cooA) and rcc00575 (cowN) genes, which are located upstream of the structural genes of Mo-nitrogenase, nifHDK. Disruption of cooA or cowN specifically impaired Mo-nitrogenase-dependent growth at carbon monoxide (CO) concentrations still tolerated by the wild type. The cooA gene was shown to belong to the Mo-nitrogenase regulon, which is exclusively expressed when ammonium is limiting. Its expression was activated by NifA1 and NifA2, the transcriptional activators of nifHDK. AnfA, the transcriptional activator of Fe-nitrogenase genes, repressed cooA, thereby counteracting NifA activation. CooA activated cowN expression in response to increasing CO concentrations. Base substitutions in the presumed CooA binding site located upstream of the cowN transcription start site abolished cowN expression, indicating that cowN regulation by CooA is direct. In conclusion, a transcription factor-based network controls cowN expression to protect Mo-nitrogenase (but not Fe-nitrogenase) under appropriate conditions.

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Section: Discussionmentioning

confidence: 99%

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confidence: 96%

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NifA- and CooA-Coordinated cowN Expression Sustains Nitrogen Fixation by Rhodobacter capsulatus in the Presence of Carbon Monoxide

et al. 2014

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“…In addition to Mo-dependent nitrogenase, some diazotrophs synthesize alternative Mo-independent nitrogenases, the V-and Fe-nitrogenases, containing either an iron-vanadium or an iron-only cofactor, respectively (2). Mo-nitrogenase exhibits higher specific N 2 -reducing activity than Mo-free nitrogenases, and thus, Mo-nitrogenase is the preferred enzyme, as long as sufficient concentrations of molybdate are available (3,4). When molybdate, the only bioavailable form of molybdenum, becomes limiting in the environment, bacteria synthesize high-affinity ModABC transporters to import molybdate against the concentration gradient (5).…”

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confidence: 99%

Coordinated Expression of fdxD and Molybdenum Nitrogenase Genes Promotes Nitrogen Fixation by Rhodobacter capsulatus in the Presence of Oxygen

et al. 2014

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Rhodobacter capsulatus is able to grow with N 2 as the sole nitrogen source using either a molybdenum-dependent or a molybdenum-free iron-only nitrogenase whose expression is strictly inhibited by ammonium. Disruption of the fdxD gene, which is located directly upstream of the Mo-nitrogenase genes, nifHDK, abolished diazotrophic growth via Mo-nitrogenase at oxygen concentrations still tolerated by the wild type, thus demonstrating the importance of FdxD under semiaerobic conditions. In contrast, FdxD was not beneficial for diazotrophic growth depending on Fe-nitrogenase. These findings suggest that the 2Fe2S ferredoxin FdxD specifically supports the Mo-nitrogenase system, probably by protecting Mo-nitrogenase against oxygen, as previously shown for its Azotobacter vinelandii counterpart, FeSII. Expression of fdxD occurred under nitrogen-fixing conditions, but not in the presence of ammonium. Expression of fdxD strictly required NifA1 and NifA2, the transcriptional activators of the Mo-nitrogenase genes, but not AnfA, the transcriptional activator of the Fe-nitrogenase genes. Expression of the fdxD and nifH genes, as well as the FdxD and NifH protein levels, increased with increasing molybdate concentrations. Molybdate induction of fdxD was independent of the molybdate-sensing regulators MopA and MopB, which repress anfA transcription at micromolar molybdate concentrations. In this report, we demonstrate the physiological relevance of an fesII-like gene, fdxD, and show that the cellular nitrogen and molybdenum statuses are integrated to control its expression.

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“…In addition to Mo-nitrogenases, some bacteria synthesize alternative Mo-free nitrogenases, which contain either an iron-vanadium cofactor, FeVco, or an iron-only cofactor, FeFeco (2). Alternative nitrogenases are less efficient than Monitrogenases in terms of consumption of reducing power and ATP per molecule of N 2 fixed (3,4). Consequently, diazotrophs preferentially utilize Mo-nitrogenase as long as sufficient molybdate, the only bioavailable form of molybdenum, is available.…”

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Proteome Profiling of the Rhodobacter capsulatus Molybdenum Response Reveals a Role of IscN in Nitrogen Fixation by Fe-Nitrogenase

et al. 2016

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Rhodobacter capsulatus is capable of synthesizing two nitrogenases, a molybdenum-dependent nitrogenase and an alternative Mo-free iron-only nitrogenase, enabling this diazotroph to grow with molecular dinitrogen (N 2 ) as the sole nitrogen source. Here, the Mo responses of the wild type and of a mutant lacking ModABC, the high-affinity molybdate transporter, were examined by proteome profiling, Western analysis, epitope tagging, and lacZ reporter fusions. Biological nitrogen fixation (BNF) is a central process in the global nitrogen cycle, which converts chemically inert atmospheric dinitrogen to ammonia, a bioavailable form of nitrogen. BNF is catalyzed by complex metalloenzymes called nitrogenases, which are exclusively found in diazotrophic bacteria and archaea but not in eukaryotes (1). All diazotrophs synthesize a molybdenum-dependent nitrogenase containing an iron-molybdenum cofactor, FeMoco. In addition to Mo-nitrogenases, some bacteria synthesize alternative Mo-free nitrogenases, which contain either an iron-vanadium cofactor, FeVco, or an iron-only cofactor, FeFeco (2). Alternative nitrogenases are less efficient than Monitrogenases in terms of consumption of reducing power and ATP per molecule of N 2 fixed (3, 4). Consequently, diazotrophs preferentially utilize Mo-nitrogenase as long as sufficient molybdate, the only bioavailable form of molybdenum, is available. To support Mo-nitrogenase activity under Mo-limiting conditions, most diazotrophs synthesize a high-affinity molybdate transporter, ModABC (1).The purple nonsulfur alphaproteobacterium Rhodobacter capsulatus is known for its metabolic versatility, and it has been used for decades as a model organism to study photosynthesis, hydrogen production, and nitrogen fixation (5-9). In particular, it is capable of using light energy to generate the ATP required for the energetically demanding nitrogen fixation process. R. capsulatus synthesizes two nitrogenases, namely, a Mo-nitrogenase and a Fenitrogenase but no V-nitrogenase (10, 11). The synthesis and activity of the two nitrogenases are controlled at the transcriptional, translational, and posttranslational levels by a regulatory cascade responding to ammonium and Mo availability (8, 9). Upon ammonium limitation, the nitrogen regulatory protein NtrC becomes activated by phosphorylation. In turn, NtrC-P activates transcription of nifA and anfA, which encode the transcription activators of Mo-nitrogenase and Fe-nitrogenase genes, respectively. At high Mo concentrations, anfA transcription is repressed by two structurally and functionally related Mo-responsive regu-

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Vanadium nitrogenase: A two-hit wonder?

Cited by 121 publications

References 53 publications

NifA- and CooA-Coordinated cowN Expression Sustains Nitrogen Fixation by Rhodobacter capsulatus in the Presence of Carbon Monoxide

NifA- and CooA-Coordinated cowN Expression Sustains Nitrogen Fixation by Rhodobacter capsulatus in the Presence of Carbon Monoxide

Coordinated Expression of fdxD and Molybdenum Nitrogenase Genes Promotes Nitrogen Fixation by Rhodobacter capsulatus in the Presence of Oxygen

Proteome Profiling of the Rhodobacter capsulatus Molybdenum Response Reveals a Role of IscN in Nitrogen Fixation by Fe-Nitrogenase

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