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To overproduce biotechnologically valuable products, the expression level of target genes has been modulated by using strong promoters. In a hyperthermophilic archaeon Thermococcus onnurineus NA1, two promoters, P sub(TN0413) and P sub(TN0157), which drive expression of the genes encoding the S-layer protein and glutamate dehydrogenase were inserted in front of a gene cluster encoding a carbon monoxide dehydrogenase, a hydrogenase and a Na super(+)/H super(+) antiporter. Two promoters exhibited strong activity by increasing the transcription and translation levels of the gene cluster in the mutant strains by 2.5- to 49-folds and 1.4- to 3.3-folds, respectively, than the native promoter in the wild-type strain. While KS0413 with P sub( TN0413) promoter exhibited 2.7 to 4.7 times higher transcript level than KS0157 with P sub(TN0157) promoter, the levels of proteins were a little different between them. The biomass concentrations and H sub(2) production rates of two mutants were 2- to 3-fold higher than those of the wild-type strain in a bioreactor where CO was supplied at a flow rate of 120 ml min super(-1). Two mutants showed differential response to the higher CO flow rate, 240 ml min super(-1), in terms of growth pattern and product formation, indicating two promoters were regulated by culture conditions. The results demonstrate that not only promoter strength but also product-forming conditions should be considered in promoter engineering.

AAA super(+ )ATPases are ubiquitous enzymes that can function as molecular chaperones, employing the energy obtained from ATP hydrolysis to remodel macromolecules. In this report, the MoxR enzyme from Thermococcus kodakarensis KOD1 (TkMoxR) was shown to have two native forms: a two-stack hexameric ring and a hexameric structure, under physiological conditions and cold stress, respectively. TkMoxR was altered to a microtubule-like form in the presence of ATP and tightly interacted with dsDNA molecules of various lengths. In addition, the two-stack hexameric protein catalyzed dsDNA decomposition to form and then release ssDNA, whereas the hexamer TkMoxR structure interacted with but did not release dsDNA. These results suggest that TkMoxR has DNA helicase activity involved in gene expression control.

Small basic proteins present in most Archaea share a common ancestor with the eukaryotic core histones. We report the crystal structure of an archaeal histone-DNA complex. DNA wraps around an extended polymer, formed by archaeal histone homodimers, in a quasi-continuous superhelix with the same geometry as DNA in the eukaryotic nucleosome. Substitutions of a conserved glycine at the interface of adjacent protein layers destabilize archaeal chromatin, reduce growth rate, and impair transcription regulation, confirming the biological importance of the polymeric structure. Our data establish that the histone-based mechanism of DNA compaction predates the nucleosome, illuminating the origin of the nucleosome.

Thermococcus onnurineus NA1 is known to grow by the anaerobic oxidation of formate to CO ₂ and H ₂, a reaction that operates near thermodynamic equilibrium. Here we demonstrate that this reaction is coupled to ATP synthesis by a transmembrane ion current. Formate oxidation leads to H ⁺ translocation across the cytoplasmic membrane that then drives Na ⁺ translocation. The ion-translocating electron transfer system is rather simple, consisting of only a formate dehydrogenase module, a membrane-bound hydrogenase module, and a multisubunit Na ⁺/H ⁺ antiporter module. The electrochemical Na ⁺ gradient established then drives ATP synthesis. These data give a mechanistic explanation for chemiosmotic energy conservation coupled to formate oxidation to CO ₂ and H ₂. Because it is discussed that the membrane-bound hydrogenase with the Na ⁺/H ⁺ antiporter module are ancestors of complex I of mitochondrial and bacterial electron transport these data also shed light on the evolution of ion transport in complex I-like electron transport chains.

Microbes that generate copious amounts of hydrogen (H 2 ) via dark fermentation are a promising means to evolve and improve renewable biofuels. Many anaerobic hyperthermophilic archaea, such as the fast-growing, genetically tractable, heterotroph Thermococcus kodakarensis , produce generous quantities of H 2 and provide an idealized platform to further optimize naturally high levels of biohydrogen reduction. Precise genetic manipulations and modifications to growth conditions have already resulted in substantial increases to H 2 output but additional improvements are desired. An unexamined and potentially valuable route towards increased H 2 production is to tether select electron donor and acceptor proteins together to reroute and maximize the flow of electrons towards H 2 production. Such strategies have shown promise in Bacteria and Eukarya but have not yet been investigated in thermophilic Archaea. Here, we generate and evaluate twelve novel T. kodakarensis strains wherein a proteinaceous electron carrier (a ferredoxin, Fd) is physically tethered to the membrane-bound-hydrogenase (MBH), the sole H 2 producing enzyme, to direct electron flux towards biohydrogen generation. Growth assessments and H 2 output measurements demonstrate that strains encoding protein-fusions evolve up to ~ 40% more H 2 per cell than the host strain. Eliminating H 2 consumption and alternative routes of electron sinks in concert with protein tethering further increased H 2 output per cell for a maximum increase of ~ 66% over the host strain. Our results demonstrate that rerouting electron flux via protein tethering coupled with the elimination of reductant sinks is a promising means towards improved biohydrogen production in T. kodakarensis . Key points Protein tethering between redox proteins can reroute electron flux in vivo. Enforced protein proximity results in ~ 40% increases in H 2 production per cell. Protein-tethering provides a generalizable framework to redirect redox metabolism.

The ribonuclease FttA (also known as aCPSF and aCPSF1) mediates factor-dependent transcription termination in archaea 1 – 3 . Here we report the structure of a Thermococcus kodakarensis transcription pre-termination complex comprising FttA, Spt4, Spt5 and a transcription elongation complex (TEC). The structure shows that FttA interacts with the TEC in a manner that enables RNA to proceed directly from the TEC RNA-exit channel to the FttA catalytic centre and that enables endonucleolytic cleavage of RNA by FttA, followed by 5′→3′ exonucleolytic cleavage of RNA by FttA and concomitant 5′→3′ translocation of FttA on RNA, to apply mechanical force to the TEC and trigger termination. The structure further reveals that Spt5 bridges FttA and the TEC, explaining how Spt5 stimulates FttA-dependent termination. The results reveal functional analogy between bacterial and archaeal factor-dependent termination, functional homology between archaeal and eukaryotic factor-dependent termination, and fundamental mechanistic similarities in factor-dependent termination in bacteria, archaea, and eukaryotes. Cryo-electron microscopy structures of the Thermococcus kodakarensis transcription pre-termination complex suggest a mechanism by which the archaeal termination factor FttA applies mechanical force to a transcription elongation complex to trigger termination, and reveal similarities in factor-dependent termination in bacteria, archaea, and eukaryotes.

High-energy electrons liberated during catabolic processes can be exploited for energy-conserving mechanisms. Maximal energy gains demand these valuable electrons be accurately shuttled from electron donor to appropriate electron acceptor. Proteinaceous electron carriers such as ferredoxins offer opportunities to exploit specific ferredoxin partnerships to ensure that electron flux to critical physiological pathways is aligned with maximal energy gains. Most species encode many ferredoxin isoforms, but very little is known about the role of individual ferredoxins in most systems. Our results detail that ferredoxin isoforms make largely unique and distinct protein interactions in vivo and that flux through one ferredoxin often cannot be recovered by flux through a different ferredoxin isoform. The results obtained more broadly suggest that ferredoxin isoforms throughout biological life have evolved not as generic electron shuttles, but rather serve as selective couriers of valuable low-potential electrons from select electron donors to desirable electron acceptors. Control of electron flux is critical in both natural and bioengineered systems to maximize energy gains. Both small molecules and proteins shuttle high-energy, low-potential electrons liberated during catabolism through diverse metabolic landscapes. Ferredoxin (Fd) proteins—an abundant class of Fe-S-containing small proteins—are essential in many species for energy conservation and ATP production strategies. It remains difficult to model electron flow through complicated metabolisms and in systems in which multiple Fd proteins are present. The overlap of activity and/or limitations of electron flux through each Fd can limit physiology and metabolic engineering strategies. Here we establish the interplay, reactivity, and physiological role(s) of the three ferredoxin proteins in the model hyperthermophile Thermococcus kodakarensis . We demonstrate that the three loci encoding known Fds are subject to distinct regulatory mechanisms and that specific Fds are utilized to shuttle electrons to separate respiratory and energy production complexes during different physiological states. The results obtained argue that unique physiological roles have been established for each Fd and that continued use of T. kodakarensis and related hydrogen-evolving species as bioengineering platforms must account for the distinct Fd partnerships that limit flux to desired electron acceptors. Extrapolating our results more broadly, the retention of multiple Fd isoforms in most species argues that specialized Fd partnerships are likely to influence electron flux throughout biology. IMPORTANCE High-energy electrons liberated during catabolic processes can be exploited for energy-conserving mechanisms. Maximal energy gains demand these valuable electrons be accurately shuttled from electron donor to appropriate electron acceptor. Proteinaceous electron carriers such as ferredoxins offer opportunities to exploit specific ferredoxin partnerships to ensure that electron flux to critical physiological pathways is aligned with maximal energy gains. Most species encode many ferredoxin isoforms, but very little is known about the role of individual ferredoxins in most systems. Our results detail that ferredoxin isoforms make largely unique and distinct protein interactions in vivo and that flux through one ferredoxin often cannot be recovered by flux through a different ferredoxin isoform. The results obtained more broadly suggest that ferredoxin isoforms throughout biological life have evolved not as generic electron shuttles, but rather serve as selective couriers of valuable low-potential electrons from select electron donors to desirable electron acceptors.

A strong promoter increases transcription of the genes of interest and enhances the production of various valuable substances. For a hyperthermophilic archaeon Thermococcus onnurineus NA1, which can produce H sub(2) from carbon monoxide oxidation, we searched for a novel endogenous strong promoter by transcriptome analysis using high-throughput RNA sequencing. Based on the relative transcript abundance, we selected one promoter to encode a hypothetical gene, of which homologs were found only in several Thermococcales strains. This promoter, PTN0510 , was introduced into the front of CO-responsible hydrogenase gene cluster encoding a carbon monoxide dehydrogenase (CODH), a hydrogenase, and a Na super(+)/H super(+) antiporter. In the resulting mutant strain, KS0510, transcription and translation level of the gene cluster increased by 4- to 14-folds and 1.5- to 1.9-folds, respectively, in comparison with those of the wild-type strain. Additionally, H sub(2) production rate of KS0510 mutant was 4.8-fold higher than that of the wild-type strain. The PTN0510 was identified to be much stronger than the well-known two strong promoters, gdh and slp promoters from Thermococcus strains, through RT-qPCR and Western blotting analyses and kinetics of H sub(2) production. In this study, we demonstrated that the RNA-seq approach is a good strategy to mine novel strong promoters of use to a Thermococcus strain when developed as a biotechnologically promising strain to produce valuable products such as enzymes and metabolites through metabolic engineering.

Opening of the DNA binding cleft of cellular RNA polymerase (RNAP) is necessary for transcription initiation but the underlying molecular mechanism is not known. Here, we report on the cryo-electron microscopy structures of the RNAP, RNAP-TFEα binary, and RNAP-TFEα-promoter DNA ternary complexes from archaea, Thermococcus kodakarensis ( Tko ). The structures reveal that TFEα bridges the RNAP clamp and stalk domains to open the DNA binding cleft. Positioning of promoter DNA into the cleft closes it while maintaining the TFEα interactions with the RNAP mobile modules. The structures and photo-crosslinking results also suggest that the conserved aromatic residue in the extended winged-helix domain of TFEα interacts with promoter DNA to stabilize the transcription bubble. This study provides a structural basis for the functions of TFEα and elucidates the mechanism by which the DNA binding cleft is opened during transcription initiation in the stalk-containing RNAPs, including archaeal and eukaryotic RNAPs. How clamp conformation is regulated in the transcription cycle of stalk-containing archaeal and eukaryotic RNA polymerase (RNAP) systems is still not well understood. Here, the authors combine cryo-EM, X-ray crystallography and photo-crosslinking assays to structurally characterise RNAP, the RNAP-TFEα binary and RNAP-TFEα-promoter DNA ternary complexes from the archaea Thermococcus kodakarensis and enables them to describe the dynamic conformational changes of the general transcription factor TFEα and RNAP during the early stage of transcription cycle.

TK0149 (designated as Tk-PdaD) of a hyperthermophilic archaeon, Thermococcus kodakaraensis, was annotated as pyruvoyl-dependent arginine decarboxylase, which catalyzes agmatine formation by the decarboxylation of arginine as the first step of polyamine biosynthesis. In order to investigate its physiological roles, Tk-PdaD was purified as a recombinant form, and its substrate dependency was examined using the candidate compounds arginine, ornithine and lysine. Tk-PdaD, expressed in Escherichia coli, was cleaved into α and β subunits, as other pyruvoyl-dependent enzymes, and the resulting subunits formed an (αβ)₆ complex. The Tk-PdaD complex catalyzed the decarboxylation of arginine but not that of ornithine and lysine. A gene disruptant lacking Tk-pdaD was constructed, showing that it grew only in the medium in the presence of agmatine but not in the absence of agmatine. The obtained results indicate that Tk-pdaD encodes a pyruvoyl-dependent arginine decarboxylase and that agmatine is essential for the cell growth of T. kodakaraensis.