title: Cyclohexa-1,5-diene-1-carbonyl-coenzyme A (CoA) hydratases of Geobacter metallireducens and Syntrophus aciditrophicus: Evidence for a common benzoyl-CoA degradation pathway in facultative and strict anaerobes.
abstract: In the denitrifying bacterium Thauera aromatica, the central intermediate of anaerobic aromatic metabolism, benzoyl-coenzyme A (CoA), is dearomatized by the ATP-dependent benzoyl-CoA reductase to cyclohexa-1,5-diene-1-carbonyl-CoA (dienoyl-CoA). The dienoyl-CoA is further metabolized by a series of beta-oxidation-like reactions of the so-called benzoyl-CoA degradation pathway resulting in ring cleavage. Recently, evidence was obtained that obligately anaerobic bacteria that use aromatic growth substrates do not contain an ATP-dependent benzoyl-CoA reductase. In these bacteria, the reactions involved in dearomatization and cleavage of the aromatic ring have not been shown, so far. In this work, a characteristic enzymatic step of the benzoyl-CoA pathway in obligate anaerobes was demonstrated and characterized. Dienoyl-CoA hydratase activities were determined in extracts of Geobacter metallireducens (iron reducing), Syntrophus aciditrophicus (fermenting), and Desulfococcus multivorans (sulfate reducing) cells grown with benzoate. The benzoate-induced genes putatively coding for the dienoyl-CoA hydratases in the benzoate degraders G. metallireducens and S. aciditrophicus were heterologously expressed and characterized. Both gene products specifically catalyzed the reversible hydration of dienoyl-CoA to 6-hydroxycyclohexenoyl-CoA (Km, 80 and 35 microM; Vmax, 350 and 550 micromol min(-1) mg(-1), respectively). Neither enzyme had significant activity with cyclohex-1-ene-1-carbonyl-CoA or crotonyl-CoA. The results suggest that benzoyl-CoA degradation proceeds via dienoyl-CoA and 6-hydroxycyclohexanoyl-CoA in strictly anaerobic bacteria. The steps involved in dienoyl-CoA metabolism appear identical in all nonphotosynthetic anaerobic bacteria, although totally different benzene ring-dearomatizing enzymes are present in facultative and obligate anaerobes.
authors.affiliation: Institute for Biology II, Microbiology, University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Peters
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Shinoda
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McInerney
authors.forename: Matthias
authors.initials: M
authors.lastname: Boll
mesh_terms: D000214:Acyl Coenzyme A / Q000737:chemistry / Q000378:metabolism*; D000693:Anaerobiosis; D020564:Deltaproteobacteria / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004746:Enoyl-CoA Hydratase / Q000235:genetics / Q000378:metabolism*; D045302:Geobacter / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D015394:Molecular Structure; D010802:Phylogeny; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D011993:Recombinant Fusion Proteins; C037817:benzoyl-coenzyme A; D004746:Enoyl-CoA Hydratase