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PDBsum entry 4l1f
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Electron transport
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PDB id
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4l1f
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References listed in PDB file
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Key reference
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Title
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Studies on the mechanism of electron bifurcation catalyzed by electron transferring flavoprotein (etf) and butyryl-Coa dehydrogenase (bcd) of acidaminococcus fermentans.
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Authors
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N.P.Chowdhury,
A.M.Mowafy,
J.K.Demmer,
V.Upadhyay,
S.Koelzer,
E.Jayamani,
J.Kahnt,
M.Hornung,
U.Demmer,
U.Ermler,
W.Buckel.
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Ref.
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J Biol Chem, 2014,
289,
5145-5157.
[DOI no: ]
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PubMed id
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Abstract
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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.
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