Enzymes of the benzoyl‐coenzyme A degradation pathway in the hyperthermophilic archaeon Ferroglobus placidus

Abstract

The Fe(III)-respiring Ferroglobus placidus is the only known archaeon and hyperthermophile for which a complete degradation of aromatic substrates to CO2 has been reported. Recent genome and transcriptome analyses proposed a benzoyl-coenzyme A (CoA) degradation pathway similar to that found in the phototrophic Rhodopseudomonas palustris, which involves a cyclohex-1-ene-1-carboxyl-CoA (1-enoyl-CoA) forming, ATP-dependent key enzyme benzoyl-CoA reductase (BCR). In this work, we demonstrate, by first in vitro studies, that benzoyl-CoA is ATP-dependently reduced by two electrons to cyclohexa-1,5-dienoyl-CoA (1,5-dienoyl-CoA), which is further degraded by hydration to 6-hydroxycyclohex-1-ene-1-carboxyl-CoA (6-OH-1-enoyl-CoA); upon addition of NAD(+) , the latter was subsequently converted to β-oxidation intermediates. The four candidate genes of BCR were heterologously expressed, and the enriched, oxygen-sensitive enzyme catalysed the two-electron reduction of benzoyl-CoA to 1,5-dienoyl-CoA. A gene previously assigned to a 2,3-didehydropimeloyl-CoA hydratase was heterologously expressed and shown to act as a typical 1,5-dienoyl-CoA hydratase that does not accept 1-enoyl-CoA. A gene previously assigned to a 1-enoyl-CoA hydratase was heterologously expressed and identified to code for a bifunctional crotonase/3-OH-butyryl-CoA dehydrogenase. In summary, the results consistently provide biochemical evidence that F. placidus and probably other archaea predominantly degrade aromatics via the Thauera/Azoarcus type and not or only to a minor extent via the predicted R. palustris-type benzoyl-CoA degradation pathway.

Structure and Function of the Unusual Tungsten Enzymes Acetylene Hydratase and Class II Benzoyl-Coenzyme A Reductase

“…Class I BCRs have been found in facultatively anaerobic bacteria and in the aromatic compound degrading archaeon Ferroglobus placidus [Holmes et al, 2012;Schmid et al, 2015]. It belongs to the recently introduced BCR/HAD family of radical enzymes that drive lowpotential single electron transfer steps to a stoichiometric ATP hydrolysis; they usually contain exclusively [4Fe-4S] clusters as cofactors [Buckel et al, 2014].…”

“…the obligately anaerobic euryarchaeon Ferroglobus placidus uses a class I BCR for the degradation of numerous aromatics such as benzene, toluene or phenol coupled to dissimilatory Fe(III) reduction; the ATP dependence of the enzyme has recently been demonstrated in vitro [Schmid et al, 2015]. Other examples are dearomatizing aryl-CoA reductases from polycyclic aromatic compound-degrading anaerobes, e.g.…”

Evolution of a xenobiotic degradation pathway: formation and capture of the labile phthaloyl‐CoA intermediate during anaerobic phthalate degradation

“…In these assays the proposed phthaloyl‐CoA intermediate was not detected by UPLC‐UV/vis analyses and its formation could only qualitatively be demonstrated by mass spectrometry (MS) (Ebenau‐Jehle et al ., ; Junghare et al ., ). The benzoyl‐CoA formed is then dearomatized by class I benzoyl‐CoA reductase (Buckel et al ., ) and further degraded by enzymes of the benzoyl‐CoA degradation pathway (Fuchs et al ., ; Díaz et al ., ; Schmid et al ., ).…”

Enzymes involved in phthalate degradation in sulphate‐reducing bacteria

“…In denitrifying bacteria, benzoyl-CoA is dearomatized by ATPdependent class I benzoyl-CoA reductases (Kung et al, 2010;Boll et al, 2014;Buckel et al, 2014;Tiedt et al, 2018). The cyclic dienoyl-CoA product is then converted to three acetyl-CoA and CO 2 by modified β-oxidation reactions of the benzoyl-CoA degradation pathway (Rabus et al, 2005;Fuchs et al, 2011;Schmid et al, 2015;Rabus et al, 2016).…”