Studies on the mechanism of electron bifurcation catalyzed by electron transferring flavoprotein (Etf) and butyryl-CoA dehydrogenase (Bcd) of Acidaminococcus fermentans

J Biol Chem. 2014 Feb 21;289(8):5145-57. doi: 10.1074/jbc.M113.521013. Epub 2013 Dec 30.

Abstract

Electron bifurcation is a fundamental strategy of energy coupling originally discovered in the Q-cycle of many organisms. Recently a flavin-based electron bifurcation has been detected in anaerobes, first in clostridia and later in acetogens and methanogens. It enables anaerobic bacteria and archaea to reduce the low-potential [4Fe-4S] clusters of ferredoxin, which increases the efficiency of the substrate level and electron transport phosphorylations. Here we characterize the bifurcating electron transferring flavoprotein (EtfAf) and butyryl-CoA dehydrogenase (BcdAf) of Acidaminococcus fermentans, which couple the exergonic reduction of crotonyl-CoA to butyryl-CoA to the endergonic reduction of ferredoxin both with NADH. EtfAf contains one FAD (α-FAD) in subunit α and a second FAD (β-FAD) in subunit β. The distance between the two isoalloxazine rings is 18 Å. The EtfAf-NAD(+) complex structure revealed β-FAD as acceptor of the hydride of NADH. The formed β-FADH(-) is considered as the bifurcating electron donor. As a result of a domain movement, α-FAD is able to approach β-FADH(-) by about 4 Å and to take up one electron yielding a stable anionic semiquinone, α-FAD, which donates this electron further to Dh-FAD of BcdAf after a second domain movement. The remaining non-stabilized neutral semiquinone, β-FADH(•), immediately reduces ferredoxin. Repetition of this process affords a second reduced ferredoxin and Dh-FADH(-) that converts crotonyl-CoA to butyryl-CoA.

Keywords: Bioenergetics/Electron Transfer Complex; Coenzyme A; Crystal Structure; Electron Transfer; Energy Metabolism; Enzyme Mechanisms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acidaminococcus / enzymology*
  • Biocatalysis*
  • Butyryl-CoA Dehydrogenase / chemistry
  • Butyryl-CoA Dehydrogenase / metabolism*
  • Crystallography, X-Ray
  • Electron Transport
  • Electron-Transferring Flavoproteins / chemistry
  • Electron-Transferring Flavoproteins / metabolism*
  • Electrons*
  • Electrophoresis, Polyacrylamide Gel
  • Ferredoxins / chemistry
  • Ferredoxins / metabolism
  • Flavin-Adenine Dinucleotide / chemistry
  • Flavin-Adenine Dinucleotide / metabolism
  • Flavins / chemistry
  • Flavins / metabolism
  • Kinetics
  • Models, Biological
  • Molecular Docking Simulation
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Spectrophotometry, Ultraviolet

Substances

  • Electron-Transferring Flavoproteins
  • Ferredoxins
  • Flavins
  • Recombinant Proteins
  • Flavin-Adenine Dinucleotide
  • isoalloxazine
  • Butyryl-CoA Dehydrogenase

Associated data

  • PDB/4KPU
  • PDB/4L1F
  • PDB/4L21