title: An electron-bifurcating caffeyl-CoA reductase.
abstract: A low potential electron carrier ferredoxin (E0' ≈ -500 mV) is used to fuel the only bioenergetic coupling site, a sodium-motive ferredoxin:NAD(+) oxidoreductase (Rnf) in the acetogenic bacterium Acetobacterium woodii. Because ferredoxin reduction with physiological electron donors is highly endergonic, it must be coupled to an exergonic reaction. One candidate is NADH-dependent caffeyl-CoA reduction. We have purified a complex from A. woodii that contains a caffeyl-CoA reductase and an electron transfer flavoprotein. The enzyme contains three subunits encoded by the carCDE genes and is predicted to have, in addition to FAD, two [4Fe-4S] clusters as cofactor, which is consistent with the experimental determination of 4 mol of FAD, 9 mol of iron, and 9 mol of acid-labile sulfur. The enzyme complex catalyzed caffeyl-CoA-dependent oxidation of reduced methyl viologen. With NADH as donor, it catalyzed caffeyl-CoA reduction, but this reaction was highly stimulated by the addition of ferredoxin. Spectroscopic analyses revealed that ferredoxin and caffeyl-CoA were reduced simultaneously, and a stoichiometry of 1.3:1 was determined. Apparently, the caffeyl-CoA reductase-Etf complex of A. woodii uses the novel mechanism of flavin-dependent electron bifurcation to drive the endergonic ferredoxin reduction with NADH as reductant by coupling it to the exergonic NADH-dependent reduction of caffeyl-CoA.
authors.affiliation: Department of Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe-Universität Frankfurt am Main, 60438 Frankfurt, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Bertsch
authors.forename: Anutthaman
authors.initials: A
authors.lastname: Parthasarathy
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Buckel
authors.forename: Volker
authors.initials: V
authors.lastname: Müller
mesh_terms: D045855:Acetobacterium / Q000201:enzymology*; D000214:Acyl Coenzyme A / Q000737:chemistry / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D002109:Caffeic Acids / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry / Q000378:metabolism; D005420:Flavoproteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D021122:Protein Subunits / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D001426:Bacterial Proteins; D002109:Caffeic Acids; D005420:Flavoproteins; D021122:Protein Subunits; D005182:Flavin-Adenine Dinucleotide; D007501:Iron; D000445:Aldehyde Oxidoreductases; C021351:hexadecanal dehydrogenase (acylating); C040048:caffeic acid