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Enhancer binding proteins (EBPs) are key players of σ54‐regulation that control transcription in response to environmental signals. In the anaerobic microorganism Desulfovibrio vulgaris Hildenborough (DvH), orp operons have been previously shown to be coregulated by σ54‐RNA polymerase, the integration host factor IHF and a cognate EBP, OrpR. In this study, ChIP‐seq experiments indicated that the OrpR regulon consists of only the two divergent orp operons. In vivo data revealed that (i) OrpR is absolutely required for orp operons transcription, (ii) under anaerobic conditions, OrpR binds on the two dedicated DNA binding sites and leads to high expression levels of the orp operons, (iii) increasing the redox potential of the medium leads to a drastic down‐regulation of the orp operons expression. Moreover, combining functional and biophysical studies on the anaerobically purified OrpR leads us to propose that OrpR senses redox potential variations via a redox‐sensitive [4Fe–4S]2+ cluster in the sensory PAS domain. Overall, the study herein presents the first characterization of a new Fe–S redox regulator belonging to the σ54‐dependent transcriptional regulator family probably advantageously selected by cells adapted to the anaerobic lifestyle to monitor redox stress conditions. [ABSTRACT FROM AUTHOR]

CO dehydrogenases (CODHs) catalyse the reversible conversion between CO and CO2. Genomic analysis indicated that the metabolic functions of CODHs vary. The genome of Carboxydothermus hydrogenoformans encodes five CODHs (CODH-I-V), of which CODH-IV is found in a gene cluster near a peroxide-reducing enzyme. Our kinetic and crystallographic experiments reveal that CODH-IV differs from other CODHs in several characteristic properties: it has a very high affinity for CO, oxidizes CO at diffusion-limited rate over a wide range of temperatures, and is more tolerant to oxygen than CODH-II. Thus, our observations support the idea that CODH-IV is a CO scavenger in defence against oxidative stress and highlight that CODHs are more diverse in terms of reactivity than expected. [ABSTRACT FROM AUTHOR]

CO‐Dehydrogenasen (CODHs) katalysieren die reversible Umsetzung zwischen CO und CO2. Genomische Analysen deuten darauf hin, dass CODHs unterschiedliche metabolische Funktionen haben. Das Genom von Carboxydothermus hydrogenoformans kodiert fünf CODHs (CODH‐I–V), von denen CODH‐IV in einem Gencluster gemeinsam mit einem Peroxid‐reduzierenden Enzym vorliegt. Unsere kinetischen und kristallographischen Analysen zeigen, dass sich CODH‐IV von anderen CODHs durch charakteristische Merkmale unterscheidet: CODH‐IV hat eine hohe Affinität für CO, oxidiert CO mit diffusionslimitierter Geschwindigkeit über einen weiten Temperaturbereich und ist toleranter gegen O2 als CODH‐II. Daher stützen unsere Beobachtungen die Idee, dass CODH‐IV als CO‐Fänger bei der Abwehr von oxidativem Stress agiert und unterstreichen, dass CODHs in Bezug auf ihre Reaktivität diverser als erwartet sind. CO‐Dehydrogenasen (CODHs) katalysieren die reversible Umwandlung zwischen CO und CO2. CODH‐IV unterscheidet sich dabei von anderen CODHs, indem es als CO‐Scavenger zur Abwehr von oxidativem Stress fungiert. Dies unterstreicht, dass CODHs in Bezug auf ihre Reaktivität diverser sind als erwartet. [ABSTRACT FROM AUTHOR]

CO dehydrogenases (CODHs) catalyse the reversible conversion between CO and CO2. Genomic analysis indicated that the metabolic functions of CODHs vary. The genome of Carboxydothermus hydrogenoformans encodes five CODHs (CODH-I-V), of which CODH-IV is found in a gene cluster near a peroxide-reducing enzyme. Our kinetic and crystallographic experiments reveal that CODH-IV differs from other CODHs in several characteristic properties: it has a very high affinity for CO, oxidizes CO at diffusion-limited rate over a wide range of temperatures, and is more tolerant to oxygen than CODH-II. Thus, our observations support the idea that CODH-IV is a CO scavenger in defence against oxidative stress and highlight that CODHs are more diverse in terms of reactivity than expected. [ABSTRACT FROM AUTHOR]

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Ni-containing CO dehydrogenases (CODHs) are very efficient metalloenzymes that catalyze the conversion between CO2 and CO. They are a source of inspiration for designing CO2-reduction catalysts and can also find direct use in biotechnology. They are deemed extremely sensitive to O2, but very little is known about this aspect of their reactivity. We investigated the reaction with O2 of Carboxydothermus hydrogenoformans (Ch) CODH II and the homologous, recently characterized CODH from Desulfovi-brio vulgaris (Dv) through protein film voltammetry and solution assays (in the oxidative direction). We found that O2 reacts very quickly with the active site of CODHs, generating species that reactivate upon reduction--this was unexpected. We observed that distinct CODHs exhibit different behaviors: Dv CODH reacts half as fast with O2 than Ch CODH, and only the former fully recovers the activity upon reduction. The results raise hope that fast CO/CO2 biological conversion may be feasible under aerobic conditions. [ABSTRACT FROM AUTHOR]