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The Mechanism of Energy Coupling in H +/Na +-Pumping Membrane Pyrophosphatase-Possibilities and Probabilities. Int J Mol Sci 2022; 23:ijms23169504. [PMID: 36012762 PMCID: PMC9408878 DOI: 10.3390/ijms23169504] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 08/12/2022] [Accepted: 08/21/2022] [Indexed: 11/17/2022] Open
Abstract
Membrane pyrophosphatases (mPPases) found in plant vacuoles and some prokaryotes and protists are ancient cation pumps that couple pyrophosphate hydrolysis with the H+ and/or Na+ transport out of the cytoplasm. Because this function is reversible, mPPases play a role in maintaining the level of cytoplasmic pyrophosphate, a known regulator of numerous metabolic reactions. mPPases arouse interest because they are among the simplest membrane transporters and have no homologs among known ion pumps. Detailed phylogenetic studies have revealed various subtypes of mPPases and suggested their roles in the evolution of the "sodium" and "proton" bioenergetics. This treatise focuses on the mechanistic aspects of the transport reaction, namely, the coupling step, the role of the chemically produced proton, subunit cooperation, and the relationship between the proton and sodium ion transport. The available data identify H+-PPases as the first non-oxidoreductase pump with a "direct-coupling" mechanism, i.e., the transported proton is produced in the coupled chemical reaction. They also support a "billiard" hypothesis, which unifies the H+ and Na+ transport mechanisms in mPPase and, probably, other transporters.
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Abstract
Acetogenic bacteria are a group of strictly anaerobic bacteria that make a living from acetate formation from two molecules of CO2 via the Wood-Ljungdahl pathway (WLP). The free energy change of this reaction is very small and allows the synthesis of only a fraction of an ATP. How this pathway is coupled to energy conservation has been an enigma since its discovery ~90 years ago. Here, we describe an electron transport chain in the cytochrome- and quinone-containing acetogen Sporomusa ovata that leads from molecular hydrogen as an electron donor to an intermediate of the WLP, methylenetetrahydrofolate (methylene-tetrahydrofolate [THF]), as an electron acceptor. The catalytic site of the hydrogenase is periplasmic and likely linked cytochrome b to the membrane. We provide evidence that the MetVF-type methylenetetrahydrofolate reductase is linked proteins MvhD and HdrCBA to the cytoplasmic membrane. Membrane preparations catalyzed the H2-dependent reduction of methylene-THF to methyl-THF. In our model, a transmembrane electrochemical H+ gradient is established by both scalar and vectorial protons that leads to the synthesis of 0.5 mol ATP/mol methylene-THF by a H+-F1Fo ATP synthase. This H2- and methylene-THF-dependent electron transport chain may be present in other cytochrome-containing acetogens as well and represents a third way of chemiosmotic energy conservation in acetogens, but only in addition to the well-established respiratory enzymes Rnf and Ech. IMPORTANCE Acetogenic bacteria grow by making acetate from CO2 and are considered the first life forms on Earth since they couple CO2 reduction to the conservation of energy. How this is achieved has been an enigma ever since. Recently, two respiratory enzymes, a ferredoxin:NAD+ oxidoreductase (Rnf) and a ferredoxin:H+ oxidoreductase (Ech), have been found in cytochrome-free acetogenic model bacteria. However, some acetogens contain cytochromes in addition, and there has been a long-standing assumption of a cytochrome-containing electron transport chain in those acetogens. Here, we provide evidence for a respiratory chain in Sporomusa ovata that has a cytochrome-containing hydrogenase as the electron donor and a methylenetetrahydrofolate reductase as the terminal electron acceptor. This is the third way of chemiosmotic energy conservation found in acetogens.
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Energy Conservation in the Acetogenic Bacterium Clostridium aceticum. Microorganisms 2021; 9:microorganisms9020258. [PMID: 33513854 PMCID: PMC7911925 DOI: 10.3390/microorganisms9020258] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 01/18/2021] [Accepted: 01/20/2021] [Indexed: 12/13/2022] Open
Abstract
In times of global warming caused by the extensive use of fossil fuels, the need to capture gaseous carbon compounds is growing bigger. Several groups of microorganisms can fix the greenhouse gas CO2. Out of these, acetogenic bacteria are role models in their ability to reduce CO2 with hydrogen to acetate, which makes acetogens prime candidates for genetic modification towards biotechnological production of value-added compounds from CO2, such as biofuels. However, growth of acetogens on gaseous substrates is strongly energy-limited, and successful metabolic engineering requires a detailed knowledge of the bioenergetics. In 1939, Clostridium aceticum was the first acetogen to be described. A recent genomic study revealed that this organism contains cytochromes and therefore may use a proton gradient in its respiratory chain. We have followed up these studies and will present data that C. aceticum does not use a H+ but a Na+ gradient for ATP synthesis, established by a Na+-Rnf. Experimental data and in silico analyses enabled us to propose the biochemistry and bioenergetics of acetogenesis from H2 + CO2 in C. aceticum.
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Katsyv A, Müller V. Overcoming Energetic Barriers in Acetogenic C1 Conversion. Front Bioeng Biotechnol 2020; 8:621166. [PMID: 33425882 PMCID: PMC7793690 DOI: 10.3389/fbioe.2020.621166] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2020] [Accepted: 11/19/2020] [Indexed: 11/13/2022] Open
Abstract
Currently one of the biggest challenges for society is to combat global warming. A solution to this global threat is the implementation of a CO2-based bioeconomy and a H2-based bioenergy economy. Anaerobic lithotrophic bacteria such as the acetogenic bacteria are key players in the global carbon and H2 cycle and thus prime candidates as driving forces in a H2- and CO2-bioeconomy. Naturally, they convert two molecules of CO2via the Wood-Ljungdahl pathway (WLP) to one molecule of acetyl-CoA which can be converted to different C2-products (acetate or ethanol) or elongated to C4 (butyrate) or C5-products (caproate). Since there is no net ATP generation from acetate formation, an electron-transport phosphorylation (ETP) module is hooked up to the WLP. ETP provides the cell with additional ATP, but the ATP gain is very low, only a fraction of an ATP per mol of acetate. Since acetogens live at the thermodynamic edge of life, metabolic engineering to obtain high-value products is currently limited by the low energy status of the cells that allows for the production of only a few compounds with rather low specificity. To set the stage for acetogens as production platforms for a wide range of bioproducts from CO2, the energetic barriers have to be overcome. This review summarizes the pathway, the energetics of the pathway and describes ways to overcome energetic barriers in acetogenic C1 conversion.
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Affiliation(s)
- Alexander Katsyv
- Department of Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University, Frankfurt am Main, Germany
| | - Volker Müller
- Department of Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University, Frankfurt am Main, Germany
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Kamariah N, Huber RG, Bond PJ, Müller V, Grüber G. 3D reconstruction and flexibility of the hybrid engine Acetobacterium woodii F-ATP synthase. Biochem Biophys Res Commun 2020; 527:518-524. [PMID: 32423799 DOI: 10.1016/j.bbrc.2020.04.026] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Accepted: 04/09/2020] [Indexed: 11/16/2022]
Abstract
The Na+-translocating F1FO ATP synthase from Acetobacterium woodii (AwF-ATP synthase) with a subunit stoichiometry of α3:β3:γ:δ:ε:a:b2:(c2/3)9:c1 represents an evolutionary path between ATP-synthases and vacuolar ATPases, by containing a heteromeric rotor c-ring, composed of subunits c1, c2 and c3, and an extra loop (γ195-211) within the rotary γ subunit. Here, the recombinant AwF-ATP synthase was subjected to negative stain electron microscopy and single particle analysis. The reference free 2D class averages revealed high flexibility of the enzyme, wherein the F1 and FO domains distinctively bended to adopt multiple conformations. Moreover, both the F1 and FO domains tilted relative to each other to a maximum extent of 28° and 30°, respectively. The first 3D reconstruction of the AwF-ATP synthase was determined which accommodates well the modelled structure of the AwF-ATP synthase as well as the γ195-211-loop. Molecular simulations of the enzyme underlined the bending features and flexibility observed in the electron micrographs, and enabled assessment of the dynamics of the extra γ195-211-loop.
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Affiliation(s)
- Neelagandan Kamariah
- Nanyang Technological University, School of Biological Sciences, 60 Nanyang Drive, Singapore, 637551, Republic of Singapore
| | - Roland G Huber
- Bioinformatics Institute (BII), Agency for Science, Technology and Research (A∗STAR), #07-01 Matrix, 30 Biopolis Street, Singapore, 38671
| | - Peter J Bond
- Bioinformatics Institute (BII), Agency for Science, Technology and Research (A∗STAR), #07-01 Matrix, 30 Biopolis Street, Singapore, 38671; Department of Biological Sciences (DBS), National University of Singapore (NUS), 14 Science Drive 4, Singapore, 117543
| | - Volker Müller
- Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Max-von-Laue-Str. 9, 60438, Frankfurt, Germany
| | - Gerhard Grüber
- Nanyang Technological University, School of Biological Sciences, 60 Nanyang Drive, Singapore, 637551, Republic of Singapore; Bioinformatics Institute (BII), Agency for Science, Technology and Research (A∗STAR), #07-01 Matrix, 30 Biopolis Street, Singapore, 38671.
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Bogdanović N, Trifunović D, Sielaff H, Westphal L, Bhushan S, Müller V, Grüber G. The structural features of Acetobacterium woodii F-ATP synthase reveal the importance of the unique subunit γ-loop in Na + translocation and ATP synthesis. FEBS J 2019; 286:1894-1907. [PMID: 30791207 DOI: 10.1111/febs.14793] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Revised: 01/25/2019] [Accepted: 02/18/2019] [Indexed: 12/18/2022]
Abstract
The Na+ translocating F1 FO ATP synthase from Acetobacterium woodii shows a subunit stoichiometry of α3 :β3 :γ:δ:ε:a:b2 :(c2/3 )9 :c1 and reveals an evolutionary path between synthases and pumps involving adaptations in the rotor c-ring, which is composed of F- and vacuolar-type c subunits in a stoichiometry of 9 : 1. This hybrid turbine couples rotation with Na+ translocation in the FO part and rotation of the central stalk subunits γ-ε to drive ATP synthesis in the catalytic α3 :β3 headpiece. Here, we isolated a highly pure recombinant A. woodii F-ATP synthase and present the first projected structure of this hybrid engine as determined by negative-stain electron microscopy and single-particle analysis. The uniqueness of the A. woodii F-ATP synthase is also reflected by an extra 17 amino acid residues loop (195 TSGKVKITEETKEEKSK211 ) in subunit γ. Deleting the loop-encoding DNA sequence (γΔ195-211 ) and purifying the recombinant F-ATP synthase γΔ195-211 mutant provided a platform to study its effect in enzyme stability and activity. The recombinant F-ATP synthase γΔ195-211 mutant revealed the same subunit composition as the wild-type enzyme and a minor reduction in ATP hydrolysis. When reconstituted into proteoliposomes ATP synthesis and Na+ transport were diminished, demonstrating the importance of the γ195-211 loop in both enzymatic processes. Based on a structural model, a coupling mechanism for this enzyme is proposed, highlighting the role of the γ-loop. Finally, the γ195-211 loop of A. woodii is discussed in comparison with the extra γ-loops of mycobacterial and chloroplasts F-ATP synthases described to be involved in species-specific regulatory mechanisms.
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Affiliation(s)
- Nebojša Bogdanović
- Nanyang Technological University, School of Biological Sciences, Singapore City, Singapore
| | - Dragan Trifunović
- Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Germany
| | - Hendrik Sielaff
- Nanyang Technological University, School of Biological Sciences, Singapore City, Singapore
| | - Lars Westphal
- Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Germany
| | - Shashi Bhushan
- Nanyang Technological University, School of Biological Sciences, Singapore City, Singapore.,NTU Institute of Structural Biology, Nanyang Technological University, Singapore City, Singapore
| | - Volker Müller
- Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Germany
| | - Gerhard Grüber
- Nanyang Technological University, School of Biological Sciences, Singapore City, Singapore
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The Rnf Complex Is an Energy-Coupled Transhydrogenase Essential To Reversibly Link Cellular NADH and Ferredoxin Pools in the Acetogen Acetobacterium woodii. J Bacteriol 2018; 200:JB.00357-18. [PMID: 30126940 DOI: 10.1128/jb.00357-18] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 08/13/2018] [Indexed: 11/20/2022] Open
Abstract
The Rnf complex is a respiratory enzyme that catalyzes the oxidation of reduced ferredoxin to the reduction of NAD+, and the negative free energy change of this reaction is used to generate a transmembrane ion gradient. In one class of anaerobic acetogenic bacteria, the Rnf complex is believed to be essential for energy conservation and autotrophic growth. We describe here a methodology for markerless mutagenesis in the model bacterium of this class, Acetobacterium woodii, which enabled us to delete the rnf genes and to test their in vivo role. The rnf mutant did not grow on H2 plus CO2, nor did it produce acetate or ATP from H2 plus CO2, and ferredoxin:NAD+ oxidoreductase activity and Na+ translocation were also completely lost, supporting the hypothesis that the Rnf complex is the only respiratory enzyme in this metabolism. Unexpectedly, the mutant also did not grow on low-energy substrates, such as ethanol or lactate. Oxidation of these substrates is not coupled to the reduction of ferredoxin but only of NAD+, and we speculated that the growth phenotype is caused by a loss of reduced ferredoxin, indispensable for biosynthesis and CO2 reduction. The electron-bifurcating hydrogenase of A. woodii reduces ferredoxin, and indeed, the addition of H2 to the cultures restored growth on ethanol and lactate. This is consistent with the hypothesis that endergonic reduction of ferredoxin with NADH is driven by reverse electron transport catalyzed by the Rnf complex, which renders the Rnf complex essential also for growth on low-energy substrates.IMPORTANCE Ferredoxin and NAD+ are key electron carriers in anaerobic bacteria, but energetically, they are not equivalent, since the redox potential of ferredoxin is lower than that of the NADH/NAD+ couple. We describe by mutant studies in Acetobacterium woodii that the main function of Rnf is to energetically link cellular pools of ferredoxin and NAD+ When ferredoxin is greater than NADH, exergonic electron flow from ferredoxin to NAD+ generates a chemiosmotic potential. This is essential for energy conservation during autotrophic growth. When NADH is greater than ferredoxin, Rnf works in reverse. This reaction is essential for growth on low-energy substrates to provide reduced ferredoxin, indispensable for biosynthesis and CO2 reduction. Our studies put a new perspective on the cellular function of the membrane-bound ion-translocating Rnf complex widespread in bacteria.
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Brandt K, Müller DB, Hoffmann J, Langer JD, Brutschy B, Morgner N, Müller V. Stoichiometry and deletion analyses of subunits in the heterotrimeric F-ATP synthasecring from the acetogenic bacteriumAcetobacterium woodii. FEBS J 2015; 283:510-20. [DOI: 10.1111/febs.13606] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Revised: 11/17/2015] [Accepted: 11/23/2015] [Indexed: 11/30/2022]
Affiliation(s)
- Karsten Brandt
- Molecular Microbiology and Bioenergetics; Institute of Molecular Biosciences; Goethe University Frankfurt am Main; Germany
| | - Daniel B. Müller
- Molecular Microbiology and Bioenergetics; Institute of Molecular Biosciences; Goethe University Frankfurt am Main; Germany
| | - Jan Hoffmann
- Institute for Physical and Theoretical Chemistry; Goethe University Frankfurt am Main; Germany
| | - Julian D. Langer
- Department of Molecular Membrane Biology; Max-Planck-Institute of Biophysics; Frankfurt am Main Germany
| | - Bernd Brutschy
- Institute for Physical and Theoretical Chemistry; Goethe University Frankfurt am Main; Germany
| | - Nina Morgner
- Institute for Physical and Theoretical Chemistry; Goethe University Frankfurt am Main; Germany
| | - Volker Müller
- Molecular Microbiology and Bioenergetics; Institute of Molecular Biosciences; Goethe University Frankfurt am Main; Germany
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