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

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 (?-FAD) in subunit ? and a second FAD (?-FAD) in subunit ?. The distance between the two isoalloxazine rings is 18 Å. The EtfAf-NAD(+) complex structure revealed ?-FAD as acceptor of the hydride of NADH. The formed ?-FADH(-) is considered as the bifurcating electron donor. As a result of a domain movement, ?-FAD is able to approach ?-FADH(-) by about 4 Å and to take up one electron yielding a stable anionic semiquinone, ?-FAD, which donates this electron further to Dh-FAD of BcdAf after a second domain movement. The remaining non-stabilized neutral semiquinone, ?-FADH(•), immediately reduces ferredoxin. Repetition of this process affords a second reduced ferredoxin and Dh-FADH(-) that converts crotonyl-CoA to butyryl-CoA.

SUBMITTER: Chowdhury NP 

PROVIDER: S-EPMC3931072 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature