The class II benzoyl‐coenzyme A reductase complex from the sulfate‐reducing Desulfosarcina cetonica

Abstract

Summary Benzoyl‐CoA reductases (BCRs) catalyse a key reaction in the anaerobic degradation pathways of monocyclic aromatic substrates, the dearomatization of benzoyl‐CoA (BzCoA) to cyclohexa‐1,5‐diene‐1‐carboxyl‐CoA (1,5‐dienoyl‐CoA) at the negative redox potential limit of diffusible enzymatic substrate/product couples (E°′ = −622 mV). A 1‐MDa class II BCR complex composed of the BamBCDEGHI subunits has so far only been isolated from the Fe(III)‐respiring Geobacter metallireducens. It is supposed to drive endergonic benzene ring reduction at an active site W‐pterin cofactor by flavin‐based electron bifurcation. Here, we identified multiple copies of putative genes encoding the structural components of a class II BCR in sulfate reducing, Fe(III)‐respiring and syntrophic bacteria. A soluble 950 kDa Bam[(BC)2DEFGHI]2 complex was isolated from extracts of Desulfosarcina cetonica cells grown with benzoate/sulfate. Metal and cofactor analyses together with the identification of conserved binding motifs gave rise to 4 W‐pterins, two selenocysteines, six flavin adenine dinucleotides, four Zn, and 48 FeS clusters. The complex exhibited 1,5‐dienoyl‐CoA‐, NADPH‐ and ferredoxin‐dependent oxidoreductase activities. Our results indicate that high‐molecular class II BCR metalloenzyme machineries are remarkably conserved in strictly anaerobic bacteria with regard to subunit architecture and cofactor content, but their subcellular localization and electron acceptor preference may differ as a result of adaptations to variable energy metabolisms.

An Aerobic Hybrid Phthalate Degradation Pathway via Phthaloyl-Coenzyme A in Denitrifying Bacteria

“…Here, the major difference is that phthaloyl-CoA is formed by an ATP-dependent CoA ligase, rather than by a succinyl-CoA-dependent CoA transferase (10). Subsequent dearomatization is then achieved by an ATP-independent class II benzoyl-CoA reductase complex (17,18).…”

Enoyl-Coenzyme A Respiration via Formate Cycling in Syntrophic Bacteria

“…Next to FdhB-2, FdhB-4, and HydB, three further candidates were identified with low expect values that were assigned to the NADH/FMN-binding BamH subunits of the class II benzoyl-CoA reductase (BCR) complex ( 32 ). This assignment is based on high similarities to experimentally characterized BamH subunits ( 32 , 33 ), and by the presence of genes encoding other subunits of class II BCRs in direct vicinity of the bamH genes. Though class II BCRs exhibit NADH:viologen oxidoreductase activities that have been assigned to the BamH subunit ( 32 ), it is very unlikely that they play a significant role during crotonate fermentation because benzoyl-CoA is not a relevant intermediate of crotonate fermentation.…”

Electron-bifurcation and fluoride efflux systems inAcetobacteriumspp. drive defluorination of perfluorinated unsaturated carboxylic acids

“…Indeed, the benzoyl-CoA reductase in Thauera aromatica has been shown to reductively defluorinate 4-fluoro-benzoyl-CoA via HF elimination and further reduction, a reaction analogous to that observed here with perfluoroalkenoic acids 39 . While this class I system uses ATP to drive the formation of high energy electrons, a class II benzoyl-CoA reductase uses two flavin-base electron bifurcation steps consecutively to catalyze benzene ring reduction 40 . This one-megadalton enzyme complex uses flavin, tungsten, selenium, and more than 50 iron-sulfur clusters to achieve the E o' potential required for benzene ring reduction.…”