<sup>13</sup>C‐NMR study of acetate assimilation in <i>Thermoproteus neutrophilus</i>

Schäfer, Sigrid; Paalme, Toomas; Vilu, Raivo; Fuchs, Georg

doi:10.1111/j.1432-1033.1989.tb15262.x

Cited by 30 publications

(31 citation statements)

References 11 publications

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“…Also, the previously observed labeling data with T. neutrophilus (18) are consistent with a dicarboxylate/4-hydroxybutyrate cycle. Therefore, the autotrophic carbon fixation pathway in the Thermoproteales, for which a reductive citric acid cycle was proposed (18)(19)(20)(21)(22), needs to be reinvestigated in view of the proposed cycle.…”

Section: Comparison Of the Cycle With Other Autotrophic Pathwaysmentioning

confidence: 99%

A dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle in the hyperthermophilic Archaeum Ignicoccus hospitalis

Huber

Gallenberger

Jahn

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Ignicoccus hospitalis is an anaerobic, autotrophic, hyperthermophilic Archaeum that serves as a host for the symbiotic/parasitic Archaeum Nanoarchaeum equitans. It uses a yet unsolved autotrophic CO 2 fixation pathway that starts from acetyl-CoA (CoA), which is reductively carboxylated to pyruvate. Pyruvate is converted to phosphoenol-pyruvate (PEP), from which glucogenesis as well as oxaloacetate formation branch off. Here, we present the complete metabolic cycle by which the primary CO 2 acceptor molecule acetyl-CoA is regenerated. Oxaloacetate is reduced to succinyl-CoA by an incomplete reductive citric acid cycle lacking 2-oxoglutarate dehydrogenase or synthase. Succinyl-CoA is reduced to 4-hydroxybutyrate, which is then activated to the CoA thioester. By using the radical enzyme 4-hydroxybutyryl-CoA dehydratase, 4-hydroxybutyryl-CoA is dehydrated to crotonyl-CoA. 4-hydroxybutyryl-CoA dehydratase ͉ CO2 fixation pathway ͉ acetyl-CoA

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Section: Comparison Of the Cycle With Other Autotrophic Pathwaysmentioning

confidence: 99%

A dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle in the hyperthermophilic Archaeum Ignicoccus hospitalis

Huber

Gallenberger

Jahn

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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280

213

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“…They are mostly chemolithoautotrophs and use a new autotrophic CO 2 fixation cycle, as studied in Ignicoccus hospitalis, Pyrolobus fumarii (Desulfurococcales) (14,27,30), and Thermoproteus neutrophilus (Thermoproteales) (6,46,49,50,51,57). This autotrophic dicarboxylate/hydroxybutyrate cycle uses pyruvate synthase and phosphoenolpyruvate (PEP) carboxylase to convert acetyl coenzyme A (acetyl-CoA) plus two CO 2 molecules into succinylCoA (27,46) (Fig.…”

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confidence: 99%

Regulation of Autotrophic CO ₂ Fixation in the Archaeon Thermoproteus neutrophilus

et al. 2010

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Thermoproteus neutrophilus, a hyperthermophilic, chemolithoautotrophic, anaerobic crenarchaeon, uses a novel autotrophic CO 2 fixation pathway, the dicarboxylate/hydroxybutyrate cycle. The regulation of the central carbon metabolism was studied on the level of whole cells, enzyme activity, the proteome, transcription, and gene organization. The organism proved to be a facultative autotroph, which prefers organic acids as carbon sources that can easily feed into the metabolite pools of this cycle. Addition of the preferred carbon sources acetate, pyruvate, succinate, and 4-hydroxybutyrate to cultures resulted in stimulation of the growth rate and a diauxic growth response. The characteristic enzyme activities of the carbon fixation cycle, fumarate hydratase, fumarate reductase, succinyl coenzyme A (CoA) synthetase, and enzymes catalyzing the conversion of succinyl-CoA to crotonyl-CoA, were differentially downregulated in the presence of acetate and, to a lesser extent, in the presence of other organic substrates. This regulation pattern correlated well with the differential expression profile of the proteome as well as with the transcription of the encoding genes. The genes encoding phosphoenolpyruvate (PEP) carboxylase, fumarate reductase, and four enzymes catalyzing the conversion of succinyl-CoA to crotonyl-CoA are clustered. Two putative operons, one comprising succinyl-CoA reductase plus 4-hydroxybutyrate-CoA ligase genes and the other comprising 4-hydroxybutyryl-CoA dehydratase plus fumarate reductase genes, were divergently transcribed into leaderless mRNAs. The promoter regions were characterized and used for isolating DNA binding proteins. Besides an Alba protein, a 18-kDa protein characteristic for autotrophic Thermoproteales that bound specifically to the promoter region was identified. This system may be suitable for molecular analysis of the transcriptional regulation of autotrophy-related genes.

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“…Its product, crotonyl-CoA, is further converted to acetoacetyl-CoA and then to two acetylCoA molecules, closing the cycle and generating an additional molecule of acetyl-CoA for biosynthesis. Therefore, two different autotrophic pathways in different crenarchaeal orders share many common enzymes and intermediates.In this context, the order Thermoproteales would constitute an exception within the Crenarchaea, since the reductive citric acid cycle was proposed for Thermoproteus neutrophilus (6,(48)(49)(50)55) and Pyrobaculum islandicum (26). T. neutrophilus is a strictly anaerobic hyperthermophilic archaeon growing autotrophically by reducing sulfur with hydrogen at 85°C and neutral pH (19).…”

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confidence: 99%

“…In this context, the order Thermoproteales would constitute an exception within the Crenarchaea, since the reductive citric acid cycle was proposed for Thermoproteus neutrophilus (6,(48)(49)(50)55) and Pyrobaculum islandicum (26). T. neutrophilus is a strictly anaerobic hyperthermophilic archaeon growing autotrophically by reducing sulfur with hydrogen at 85°C and neutral pH (19).…”

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confidence: 99%

Autotrophic Carbon Dioxide Assimilation in Thermoproteales Revisited

2009

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For Crenarchaea, two new autotrophic carbon fixation cycles were recently described. Sulfolobales use the 3-hydroxypropionate/4-hydroxybutyrate cycle, with acetyl-coenzyme A (CoA)/propionyl-CoA carboxylase as the carboxylating enzyme. Ignicoccus hospitalis (Desulfurococcales) uses the dicarboxylate/4-hydroxybutyrate cycle, with pyruvate synthase and phosphoenolpyruvate carboxylase being responsible for CO 2 fixation. In the two cycles, acetyl-CoA and two inorganic carbons are transformed to succinyl-CoA by different routes, whereas the regeneration of acetyl-CoA from succinyl-CoA proceeds via the same route. Thermoproteales would be an exception to this unifying concept, since for Thermoproteus neutrophilus, the reductive citric acid cycle was proposed as a carbon fixation mechanism. Here, evidence is presented for the operation of the dicarboxylate/4-hydroxybutyrate cycle in this archaeon. All required enzyme activities were detected in large amounts. The key enzymes of the cycle were strongly upregulated under autotrophic growth conditions, indicating their involvement in autotrophic CO 2 fixation. The corresponding genes were identified in the genome.14 C-labeled 4-hydroxybutyrate was incorporated into the central building blocks in accordance with the key position of this compound in the cycle. Moreover, the results of previous 13 C-labeling studies, which could be reconciled with a reductive citric acid cycle only when some assumptions were made, were perfectly in line with the new proposal. We conclude that the dicarboxylate/4-hydroxybutyrate cycle is operating in CO 2 fixation in the strict anaerobic Thermoproteales as well as in Desulfurococcales.Two new autotrophic carbon fixation cycles have recently been discovered in the Crenarchaea, one of the two subgroups of the Archaea. The 3-hydroxypropionate/4-hydroxybutyrate cycle functions in the aerobic autotrophic Sulfolobales (7) and the dicarboxylate/4-hydroxybutyrate cycle (Fig. 1) in the anaerobic autotrophic Ignicoccus hospitalis, belonging to the Desulfurococcales (27). These pathways have in common the synthesis of succinyl-coenzyme A (CoA) from acetyl-CoA and two inorganic carbons, although this is accomplished in quite different ways and using different carboxylases. In the 3-hydroxypropionate/4-hydroxybutyrate cycle, acetyl-CoA/propionyl-CoA carboxylase fixes two molecules of bicarbonate, and in the dicarboxylate/4-hydroxybutyrate cycle, pyruvate synthase and phosphoenolpyruvate (PEP) carboxylase are the two carboxylating enzymes. Yet, the regenerations of acetyl-CoA, the primary CO 2 acceptor, from succinyl-CoA are similar in the two pathways.Acetyl-CoA regeneration is as follows. The CO 2 fixation product succinyl-CoA is reduced to 4-hydroxybutyrate, which is activated to 4-hydroxybutyryl-CoA and then dehydrated to crotonyl-CoA by 4-hydroxybutyryl-CoA dehydratase. This radical [4Fe-4S] and flavin adenine dinucleotide-containing dehydratase (11, 37) is considered a key enzyme of the 4-hydroxybutyrate part of each pathway. Its product, crotonyl-Co...

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¹³C‐NMR study of acetate assimilation in Thermoproteus neutrophilus

Cited by 30 publications

References 11 publications

A dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle in the hyperthermophilic Archaeum Ignicoccus hospitalis

A dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle in the hyperthermophilic Archaeum Ignicoccus hospitalis

Regulation of Autotrophic CO ₂ Fixation in the Archaeon Thermoproteus neutrophilus

Autotrophic Carbon Dioxide Assimilation in Thermoproteales Revisited

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13C‐NMR study of acetate assimilation in Thermoproteus neutrophilus

Cited by 30 publications

References 11 publications

A dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle in the hyperthermophilic Archaeum Ignicoccus hospitalis

A dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle in the hyperthermophilic Archaeum Ignicoccus hospitalis

Regulation of Autotrophic CO 2 Fixation in the Archaeon Thermoproteus neutrophilus

Autotrophic Carbon Dioxide Assimilation in Thermoproteales Revisited

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¹³C‐NMR study of acetate assimilation in Thermoproteus neutrophilus

Regulation of Autotrophic CO ₂ Fixation in the Archaeon Thermoproteus neutrophilus