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Results for “energy-converting hydrogenase”

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PubMed2005

Energy-converting [NiFe] hydrogenases: more than just H2 activation.

The well-characterized [NiFe] hydrogenases have a key function in the H2 metabolism of various microorganisms. A subfamily of the [NiFe] hydrogenases with unique properties has recently been identified. The six conserved subunits that build the core of these membrane-bound hydrogenases share sequence similarity with subunits that form the catalytic core of energy-conserving NADH:quinone oxidoreductases (complex I). The physiological role of some of these hydrogenases is to catalyze the reduction of H+ with electrons derived from reduced ferredoxins or polyferredoxins. This exergonic reaction is coupled to energy conservation by means of electron-transport phosphorylation. Other members of this hydrogenase subfamily mainly function in providing the cell with reduced ferredoxin using H2 as electron donor in a reaction driven by reverse electron transport. These hydrogenases have therefore been designated as energy-converting [NiFe] hydrogenases.

Aldehyde Oxidoreductases↗
PubMed2004

Energy-converting [NiFe] hydrogenases from archaea and extremophiles: ancestors of complex I.

[NiFe] hydrogenases are well-characterized enzymes that have a key function in the H2 metabolism of various microorganisms. In the recent years a subfamily of [NiFe] hydrogenases with unique properties has been identified. The members of this family form multisubunit membrane-bound enzyme complexes composed of at least four hydrophilic and two integral membrane proteins. These six conserved subunits, which built the core of these hydrogenases, have closely related counterparts in energy-conserving NADH:quinone oxidoreductases (complex I). However, the reaction catalyzed by these hydrogenases differs significantly from the reaction catalyzed by complex I. For some of these hydrogenases the physiological role is to catalyze the reduction of H+ with electrons derived from reduced ferredoxins or poly-ferredoxins. This exergonic reaction is coupled to energy conservation by means of electron-transport phosphorylation. Other members of this hydrogenase family mainly function to provide the cell with reduced ferredoxin with H2 as electron donor in a reaction driven by reverse electron transport. As complex I these hydrogenases function as ion pumps and have therefore been designated as energy-converting [NiFe] hydrogenases.

Archaea↗
PubMed2004

A multisubunit membrane-bound [NiFe] hydrogenase and an NADH-dependent Fe-only hydrogenase in the fermenting bacterium Thermoanaerobacter tengcongensis.

Thermoanaerobacter tengcongensis is a thermophilic Gram-positive bacterium able to dispose of the reducing equivalents generated during the fermentation of glucose to acetate and CO(2) by reducing H(+) to H(2). A unique combination of hydrogenases, a ferredoxin-dependent [NiFe] hydrogenase and an NADH-dependent Fe-only hydrogenase, were found to be responsible for H(2) formation in this organism. Both enzymes were purified and characterized. The tightly membrane-bound [NiFe] hydrogenase belongs to a small group of complex-I-related [NiFe] hydrogenases and has highest sequence similarity to energy-converting [NiFe] hydrogenase (Ech) from Methanosarcina barkeri. A ferredoxin isolated from Ta. tengcongensis was identified as the physiological substrate of this enzyme. The heterotetrameric Fe-only hydrogenase was isolated from the soluble fraction. It contained FMN and multiple iron-sulfur clusters, and exhibited a typical H-cluster EPR signal after autooxidation. Sequence analysis predicted and kinetic studies confirmed that the enzyme is an NAD(H)-dependent Fe-only hydrogenase. When H(2) was allowed to accumulate in the culture, the fermentation was partially shifted to ethanol production. In cells grown at high hydrogen partial pressure [p(H(2))] the NADH-dependent hydrogenase activity was fourfold lower than in cells grown at low p(H(2)), whereas aldehyde dehydrogenase and alcohol dehydrogenase activities were higher in cells grown at elevated p(H(2)). These results indicate a regulation in response to the p(H(2)).

Amino Acid Sequence↗
PubMed2026

Carbon monoxide-driven proton respiration enables facultative anaerobes to survive electron acceptor limitation.

Diverse microorganisms couple the oxidation of carbon monoxide gas (CO) to the reduction of protons, producing hydrogen gas (H2) using nickel-containing CO dehydrogenase/energy-converting hydrogenase (Ni-CODH/ECH). Although this process yields one of the lowest free-energy gains in biology, its physiological role at environmentally relevant CO levels remains unresolved. Here, we show that Ni-CODH/ECH functions as a survival-oriented energy conservation system that enables heterotrophic facultative anaerobes to survive electron acceptor limitation, rather than primarily supporting growth or CO detoxification. Analysis of 387 genomes of Anoxybacillaceae species revealed that Ni-CODH/ECH had a patchy distribution and, with one exception, was mutually exclusive with the oxygen-tolerant molybdenum-containing CODH, suggesting ecological specialization. Culture experiments using three isolates (Parageobacillus sp. G301, P. thermoglucosidasius NBRC 107763, and Thermolongibacillus altinsuensis B1-1) demonstrated that CO-dependent proton respiration is activated during stationary phase when exogenous electron acceptors are limiting, maintaining cell density under 25% CO, whereas no effect was observed in a Ni-CODH knockout (ΔcooCSF) strain. RNA-seq analysis of Parageobacillus sp. G301 under twelve conditions revealed that Ni-CODH/ECH genes are highly expressed (top 0.2%-1.9% of all genes) under electron acceptor-free conditions, independent of CO presence, under the predicted control of the redox-dependent transcriptional repressor Rex. ΔcooCSF cultures accumulated more CO than the wild-type (WT), suggesting trace CO scavenging by the WT. Together, our results redefine Ni-CODH/ECH as a redox-regulated auxiliary energy-conservation strategy that supports survival and maintenance in anaerobic energy-limited environments using two ubiquitous substrates. This work extends the carboxydovore paradigm of trace gas-based survival from aerobic to spatiotemporally variable anaerobic environments.

Carbon Monoxide↗
PubMed2004

Adjacent cysteines are capable of ligating the same tetranuclear iron-sulfur cluster.

The mechanism of the energy-converting NADH (beta-nicotinamide adenine dinucleotide, reduced form):ubiquinone oxidoreductase, which is also called respiratory complex I, is largely unknown due to lack of a high-resolution structure and the most complicated construction of the enzyme. Electron transport is carried out by one flavin mononucleotide (FMN) and up to 9 Fe/S clusters. The Fe/S cluster N2, which is believed to be directly involved in redox-coupled proton-translocation, is located on subunit NuoB (the homologue of the mitochondrial PSST subunit). This subunit contains a conserved binding motif for a [4Fe/4S] cluster with two adjacent cysteines. It was questioned whether these adjacent cysteines could be ligands of the same cluster due to a possible steric hinderance. However, mutagenesis of either of these cysteines led to a loss of cluster N2. We used the known structure of the homologous small subunit of hydrogenases containing a regular cysteine motif to generate an in silico mutant with two consecutive cysteines. Molecular dynamics simulation showed that the conformation of these cysteines does not meet the topological requirements for coordination of a [4Fe/4S] cluster when the protein backbone conformation is kept constant. In comparison, the simulation of a dipeptide amide using a "template forcing" approach resulted in a conformation compatible to an optimal coordination of the two cluster positions in question. Thus, a slight main-chain conformational change would allow two adjacent cysteines to coordinate a [4Fe/4S] cluster.

Amino Acid Motifs↗