Electron Bifurcation Makes the Puzzle Pieces Fall Energetically into Place in Methanogenic Energy Conservation

Lubner, Carolyn E.; Peters, John W.

doi:10.1002/cbic.201700533

Cited by 10 publications

(7 citation statements)

References 18 publications

(70 reference statements)

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“…MvhA contains the [NiFe]-hydrogenase active site, MvhG contains three [4Fe-4S]-clusters and MvhD contains one [2Fe-2S]-cluster; the latter is in electron-transfer distance to one of the [4Fe-4S]-clusters in HdrA. The authors discuss several possibilities of how FAD in HdrA could bifurcate the electrons on their way from H 2 to the heterodisulfide and ferredoxin; for a commentary see Lubner and Peters ( 2017 ).…”

Section: Crystal Structure Of Four Electron-bifurcating Flavoenzyme Cmentioning

confidence: 99%

Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD+ (Rnf) as Electron Acceptors: A Historical Review

2018

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Flavin-based electron bifurcation is a newly discovered mechanism, by which a hydride electron pair from NAD(P)H, coenzyme F420H2, H2, or formate is split by flavoproteins into one-electron with a more negative reduction potential and one with a more positive reduction potential than that of the electron pair. Via this mechanism microorganisms generate low- potential electrons for the reduction of ferredoxins (Fd) and flavodoxins (Fld). The first example was described in 2008 when it was found that the butyryl-CoA dehydrogenase-electron-transferring flavoprotein complex (Bcd-EtfAB) of Clostridium kluyveri couples the endergonic reduction of ferredoxin (E0′ = −420 mV) with NADH (−320 mV) to the exergonic reduction of crotonyl-CoA to butyryl-CoA (−10 mV) with NADH. The discovery was followed by the finding of an electron-bifurcating Fd- and NAD-dependent [FeFe]-hydrogenase (HydABC) in Thermotoga maritima (2009), Fd-dependent transhydrogenase (NfnAB) in various bacteria and archaea (2010), Fd- and H2-dependent heterodisulfide reductase (MvhADG-HdrABC) in methanogenic archaea (2011), Fd- and NADH-dependent caffeyl-CoA reductase (CarCDE) in Acetobacterium woodii (2013), Fd- and NAD-dependent formate dehydrogenase (HylABC-FdhF2) in Clostridium acidi-urici (2013), Fd- and NADP-dependent [FeFe]-hydrogenase (HytA-E) in Clostridium autoethanogrenum (2013), Fd(?)- and NADH-dependent methylene-tetrahydrofolate reductase (MetFV-HdrABC-MvhD) in Moorella thermoacetica (2014), Fd- and NAD-dependent lactate dehydrogenase (LctBCD) in A. woodii (2015), Fd- and F420H2-dependent heterodisulfide reductase (HdrA2B2C2) in Methanosarcina acetivorans (2017), and Fd- and NADH-dependent ubiquinol reductase (FixABCX) in Azotobacter vinelandii (2017). The electron-bifurcating flavoprotein complexes known to date fall into four groups that have evolved independently, namely those containing EtfAB (CarED, LctCB, FixBA) with bound FAD, a NuoF homolog (HydB, HytB, or HylB) harboring FMN, NfnB with bound FAD, or HdrA harboring FAD. All these flavoproteins are cytoplasmic except for the membrane-associated protein FixABCX. The organisms—in which they have been found—are strictly anaerobic microorganisms except for the aerobe A. vinelandii. The electron-bifurcating complexes are involved in a variety of processes such as butyric acid fermentation, methanogenesis, acetogenesis, anaerobic lactate oxidation, dissimilatory sulfate reduction, anaerobic- dearomatization, nitrogen fixation, and CO2 fixation. They contribute to energy conservation via the energy-converting ferredoxin: NAD+ reductase complex Rnf or the energy-converting ferredoxin-dependent hydrogenase complex Ech. This Review describes how this mechanism was discovered.

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Section: Crystal Structure Of Four Electron-bifurcating Flavoenzyme Cmentioning

confidence: 99%

Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD+ (Rnf) as Electron Acceptors: A Historical Review

2018

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“…This agrees with the historical finding by Hungate (1967) of H 2 being the main [H] donor for CH 4 formation in rumen fermentation. Interspecies H 2 transfer thermodynamically favors the reoxidation of intracellular cofactors as the H 2 -consuming microorganisms help decreasing H 2 concentration (Wolin et al, 1997;Lubner and Peters, 2017). In the presence of methanogens, or propionate or succinate producers, H 2 producers shifted fermentation away from formate, lactate and ethanol toward acetate, and cellulose digestion increased.…”

Section: The Role Of Dihydrogen As An Intercellular Electron Carriermentioning

confidence: 99%

Metabolic Hydrogen Flows in Rumen Fermentation: Principles and Possibilities of Interventions

2020

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Rumen fermentation affects ruminants productivity and the environmental impact of ruminant production. The release to the atmosphere of methane produced in the rumen is a loss of energy and a cause of climate change, and the profile of volatile fatty acids produced in the rumen affects the post-absorptive metabolism of the host animal. Rumen fermentation is shaped by intracellular and intercellular flows of metabolic hydrogen centered on the production, interspecies transfer, and incorporation of dihydrogen into competing pathways. Factors that affect the growth of methanogens and the rate of feed fermentation impact dihydrogen concentration in the rumen, which in turn controls the balance between pathways that produce and incorporate metabolic hydrogen, determining methane production and the profile of volatile fatty acids. A basic kinetic model of competition for dihydrogen is presented, and possibilities for intervention to redirect metabolic hydrogen from methanogenesis toward alternative useful electron sinks are discussed. The flows of metabolic hydrogen toward nutritionally beneficial sinks could be enhanced by adding to the rumen fermentation electron acceptors or direct fed microbials. It is proposed to screen hydrogenotrophs for dihydrogen thresholds and affinities, as well as identifying and studying microorganisms that produce and utilize intercellular electron carriers other than dihydrogen. These approaches can allow identifying potential microbial additives to compete with methanogens for metabolic hydrogen. The combination of adequate microbial additives or electron acceptors with inhibitors of methanogenesis can be effective approaches to decrease methane production and simultaneously redirect metabolic hydrogen toward end products of fermentation with a nutritional value for the host animal. The design of strategies to redirect metabolic hydrogen from methane to other sinks should be based on knowledge of the physicochemical control of rumen fermentation pathways. The application of new -omics techniques together with classical biochemistry methods and mechanistic modeling can lead to exciting developments in the understanding and manipulation of the flows of metabolic hydrogen in rumen fermentation.

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“…The reader is referred to several recent excellent reviews for overviews and discussions of the biological meaning of FBEB, and the properties of the bifurcating enzymes also in a historical and evolutionary perspective [ 19 , 21 , 22 , 118 – 122 ].…”

Section: Iron-sulfur Flavoproteins With Diverse Functions But a Common Modulementioning

confidence: 99%

“…Several of the reactions are reversible giving rise to a confurcation mechanism so that, in this back reaction, two 1-electron donors make the electrons converge on the bifurcating flavin coenzyme. The reader is referred to several recent excellent reviews for overviews and discussions of the biological meaning of FBEB, and the properties of the bifurcating enzymes also in a historical and evolutionary perspective [19,21,22,[118][119][120][121][122].…”

Section: Nfn and The Flavin-based Electron Bifurcation Mechanismmentioning

confidence: 99%

Iron-sulfur flavoenzymes: the added value of making the most ancient redox cofactors and the versatile flavins work together

Vanoni

2021

Open Biol.

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Iron-sulfur (Fe-S) flavoproteins form a broad and growing class of complex, multi-domain and often multi-subunit proteins coupling the most ancient cofactors (the Fe-S clusters) and the most versatile coenzymes (the flavin coenzymes, FMN and FAD). These enzymes catalyse oxidoreduction reactions usually acting as switches between donors of electron pairs and acceptors of single electrons, and vice versa. Through selected examples, the enzymes' structure−function relationships with respect to rate and directionality of the electron transfer steps, the role of the apoprotein and its dynamics in modulating the electron transfer process will be discussed.

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Electron Bifurcation Makes the Puzzle Pieces Fall Energetically into Place in Methanogenic Energy Conservation

Cited by 10 publications

References 18 publications

Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD+ (Rnf) as Electron Acceptors: A Historical Review

Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD+ (Rnf) as Electron Acceptors: A Historical Review

Metabolic Hydrogen Flows in Rumen Fermentation: Principles and Possibilities of Interventions

Iron-sulfur flavoenzymes: the added value of making the most ancient redox cofactors and the versatile flavins work together

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