Heterodisulfide reductase (Hdr), is an iron-sulfur protein which in anaerobic methanogenic archaea catalyzes the reduction of the disulphide bond between coenzyme M and coenzyme B and is coupled to methane formation

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	PMID	Title & Author	Abstract	Year
0	24039260	VhuD facilitates electron flow from H2 or formate to heterodisulfide reductase in Methanococcus maripaludis.Kyle C Costa 1, Thomas J Lie, Qin Xia, John A Leigh	Flavin-based electron bifurcation has recently been characterized as an essential energy conservation mechanism that is utilized by hydrogenotrophic methanogenic Archaea to generate low-potential electrons in an ATP-independent manner. Electron bifurcation likely takes place at the flavin associated with the α subunit of heterodisulfide reductase (HdrA). In Methanococcus maripaludis the electrons for this reaction come from either formate or H2 via formate dehydrogenase (Fdh) or Hdr-associated hydrogenase (Vhu). However, how these enzymes bind to HdrA to deliver electrons is unknown. Here, we present evidence that the δ subunit of hydrogenase (VhuD) is central to the interaction of both enzymes with HdrA. When M. maripaludis is grown under conditions where both Fdh and Vhu are expressed, these enzymes compete for binding to VhuD, which in turn binds to HdrA. Under these conditions, both enzymes are fully functional and are bound to VhuD in substoichiometric quantities. We also show that Fdh copurifies specifically with VhuD in the absence of other hydrogenase subunits. Surprisingly, in the absence of Vhu, growth on hydrogen still occurs; we show that this involves F420-reducing hydrogenase. The data presented here represent an initial characterization of specific protein interactions centered on Hdr in a hydrogenotrophic methanogen that utilizes multiple electron donors for growth.	2013
1	DOI: 10.1111	Structural and spectroscopic characterization of a HdrA-like subunit fromHyphomicrobium denitrificans.Ernst, C (Ernst, Corvin) ; Kayastha, K (Kayastha, Kanwal) ; Koch, T (Koch, Tobias); Venceslau, SS (Venceslau, Sofia S.); Pereira, IAC (Pereira, Ines A. C.); Demmer, U (Demmer, Ulrike) ; Ermler, U (Ermler, Ulrich) ; Dahl, C (Dahl, Christiane)	Many bacteria and archaea employ a novel pathway of sulfur oxidation involving an enzyme complex that is related to the heterodisulfide reductase (Hdr or HdrABC) of methanogens. As a first step in the biochemical characterization of Hdr-like proteins from sulfur oxidizers (sHdr), we structurally analyzed the recombinant sHdrA protein from the AlphaproteobacteriumHyphomicrobium denitrificansat 1.4 angstrom resolution. The sHdrA core structure is similar to that of methanogenic HdrA (mHdrA) which binds the electron-bifurcating flavin adenine dinucleotide (FAD), the heart of the HdrABC-[NiFe]-hydrogenase catalyzed reaction. Each sHdrA homodimer carries two FADs and two [4Fe-4S] clusters being linked by electron conductivity. Redox titrations monitored by electron paramagnetic resonance and visible spectroscopy revealed a redox potential between -203 and -188 mV for the [4Fe-4S] center. The potentials for the FADH center dot/FADH(-)and FAD/FADH center dot pairs reside between -174 and -156 mV and between -81 and -19 mV, respectively. The resulting stable semiquinone FADH center dot species already detectable in the visible and electron paramagnetic resonance spectra of the as-isolated state of sHdrA is incompatible with basic principles of flavin-based electron bifurcation such that the sHdr complex does not apply this new mode of energy coupling. The inverted one-electron FAD redox potentials of sHdr and mHdr are clearly reflected in the different FAD-polypeptide interactions. According to this finding and the assumption that the sHdr complex forms an asymmetric HdrAA ' B1C1B2C2 hexamer, we tentatively propose a mechanism that links protein-bound sulfane oxidation to sulfite on HdrB1 with NAD(+)reduction via lipoamide disulfide reduction on HdrB2. The FAD of HdrA thereby serves as an electron storage unit. Database Structural data are available in PDB database under the accession number .	2020
2	DOI: 10.4028	Heterodisulfide reductase from Acidithiobacilli is a key component involved in metabolism of reduced inorganic sulfur compounds.Ehrenfeld, N (Ehrenfeld, Nicole) ; Levican, G (Levican, Gloria) ; Parada, P (Parada, Pilar)	Heterodisulfide reductase (Hdr), is an iron-sulfur protein which in anaerobic methanogenic archaea catalyzes the reduction of the disulfide bond between coenzyme M and coenzyme B and is coupled to methane formation. In aerobic acidophilic chemolithotrophic bacteria (e.g., biomining bacteria) the function of this enzyme is unclear. Inspection of the genomic sequences of Acidithiobacillus ferrooxidans DSM 16786 and Acidithiobacillus thiooxidans DSM 17318 and reverse transcriptase-PCR results revealed a cluster of six co-transcribed genes, hdrC1, hdrB1, hdrA, orf1, hdrC2 and hdrB2, encoding proteins with high similarity to catalytic Hdr subunits. Additionally, microarray expression profiling and quantitative RT-PCR experiments demonstrated that the hdr genes of At. ferrooxidans and At. thiooxidans were highly expressed when bacteria are grown in the presence of sulfur and tetrathionate. Moreover, hdr genes in At. ferrooxidans were greatly up-regulated when this microorganism was grown in sulfur compared to ferrous medium. These results strongly support a role for Hdr in oxidative metabolism of reduced sulfur compounds in aerobic chemolithotrophic bacteria.	2013
3	27284018	Microbial oxidative sulfur metabolism: biochemical evidence of the membrane-bound heterodisulfide reductase-like complex of the bacterium Aquifex aeolicus.Souhela Boughanemi, Jordan Lyonnet, Pascale Infossi, Marielle Bauzan , Artémis Kosta , Sabrina Lignon , Marie-Thérèse Giudici-Orticoni , Marianne Guiral	The Hdr (heterodisulfide reductase)-like enzyme is predicted, from gene transcript profiling experiments previously published, to be essential in oxidative sulfur metabolism in a number of bacteria and archaea. Nevertheless, no biochemical and physicochemical data are available so far about this enzyme. Genes coding for it were identified in Aquifex aeolicus, a Gram-negative, hyperthermophilic, chemolithoautotrophic and microaerophilic bacterium that uses inorganic sulfur compounds as electron donor to grow. We provide biochemical evidence that this Hdr-like enzyme is present in this sulfur-oxidizing prokaryote (cultivated with thiosulfate or elemental sulfur). We demonstrate, by immunolocalization and cell fractionation, that Hdr-like enzyme is associated, presumably monotopically, with the membrane fraction. We show by co-immunoprecipitation assay or partial purification, that the Hdr proteins form a stable complex composed of at least five subunits, HdrA, HdrB1, HdrB2, HdrC1 and HdrC2, present in two forms of high molecular mass on native gel (∼240 and 450 kDa). These studies allow us to propose a revised model for dissimilatory sulfur oxidation pathways in A. aeolicus, with Hdr predicted to generate sulfite.	2016
4	29593673	Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD + (Rnf) as Electron Acceptors: A Historical Review.Wolfgang Buckel , Rudolf K Thauer	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.	2018
5	30973887	[NiFe]-hydrogenases are constitutively expressed in an enriched Methanobacterium sp. population during electromethanogenesis.Elisabet Perona-Vico , Ramiro Blasco-Gómez, Jesús Colprim , Sebastià Puig, Lluis Bañeras	Electromethanogenesis is the bioreduction of carbon dioxide (CO2) to methane (CH4) utilizing an electrode as electron donor. Some studies have reported the active participation of Methanobacterium sp. in electron capturing, although no conclusive results are available. In this study, we aimed at determining short-time changes in the expression levels of [NiFe]-hydrogenases (Eha, Ehb and Mvh), heterodisulfide reductase (Hdr), coenzyme F420-reducing [NiFe]-hydrogenase (Frh), and hydrogenase maturation protein (HypD), according to the electron flow in independently connected carbon cloth cathodes poised at- 800 mV vs. standard hydrogen electrode (SHE). Amplicon massive sequencing of cathode biofilm confirmed the presence of an enriched Methanobacterium sp. population (>70% of sequence reads), which remained in an active state (78% of cDNA reads), tagging this archaeon as the main methane producer in the system. Quantitative RT-PCR determinations of ehaB, ehbL, mvhA, hdrA, frhA, and hypD genes resulted in only slight (up to 1.5 fold) changes for four out of six genes analyzed when cells were exposed to open (disconnected) or closed (connected) electric circuit events. The presented results suggested that suspected mechanisms for electron capturing were not regulated at the transcriptional level in Methanobacterium sp. for short time exposures of the cells to connected-disconnected circuits. Additional tests are needed in order to confirm proteins that participate in electron capturing in Methanobacterium sp.	2019

Ehrenfeld N , Levicán, Gloria, Parada P . Heterodisulfide Reductase from Acidithiobacilli is a Key Component Involved in Metabolism of Reduced Inorganic Sulfur Compounds[J]. Advanced Materials Research, 2013, 825:194-197.