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TitleCryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX.
Journal, issue, pagesProc Natl Acad Sci U S A, Vol. 118, Issue 2, Year 2021
Publish dateJan 12, 2021
AuthorsXiang Feng / Gerrit J Schut / Gina L Lipscomb / Huilin Li / Michael W W Adams /
PubMed AbstractThe electron-transferring flavoprotein-menaquinone oxidoreductase ABCX (EtfABCX), also known as FixABCX for its role in nitrogen-fixing organisms, is a member of a family of electron-transferring ...The electron-transferring flavoprotein-menaquinone oxidoreductase ABCX (EtfABCX), also known as FixABCX for its role in nitrogen-fixing organisms, is a member of a family of electron-transferring flavoproteins that catalyze electron bifurcation. EtfABCX enables endergonic reduction of ferredoxin (°' ∼-450 mV) using NADH (°' -320 mV) as the electron donor by coupling this reaction to the exergonic reduction of menaquinone (°' -80 mV). Here we report the 2.9 Å structure of EtfABCX, a membrane-associated flavin-based electron bifurcation (FBEB) complex, from a thermophilic bacterium. EtfABCX forms a superdimer with two membrane-associated EtfCs at the dimer interface that contain two bound menaquinones. The structure reveals that, in contrast to previous predictions, the low-potential electrons bifurcated from EtfAB are most likely directly transferred to ferredoxin, while high-potential electrons reduce the quinone via two [4Fe-4S] clusters in EtfX. Surprisingly, EtfX shares remarkable structural similarity with mammalian [4Fe-4S] cluster-containing ETF ubiquinone oxidoreductase (ETF-QO), suggesting an unexpected evolutionary link between bifurcating and nonbifurcating systems. Based on this structure and spectroscopic studies of a closely related EtfABCX, we propose a detailed mechanism of the catalytic cycle and the accompanying structural changes in this membrane-associated FBEB system.
External linksProc Natl Acad Sci U S A / PubMed:33372143 / PubMed Central
MethodsEM (single particle)
Resolution2.9 Å
Structure data

22973

7koe

EMDB-22973, PDB-7koe:
Electron bifurcating flavoprotein Fix/EtfABCX
Method: EM (single particle) / Resolution: 2.9 Å

Chemicals

ChemComp-FAD:
FLAVIN-ADENINE DINUCLEOTIDE / FAD*YM

ChemComp-MQ7:
MENAQUINONE-7

ChemComp-SF4:
IRON/SULFUR CLUSTER

Source
  • Thermotoga maritima MSB8 (bacteria)
  • thermotoga maritima (strain atcc 43589 / msb8 / dsm 3109 / jcm 10099) (bacteria)
KeywordsFLAVOPROTEIN/Oxidoreductase / membrane-associated / flavin based electron bifurcation / FLAVOPROTEIN / FLAVOPROTEIN-Oxidoreductase complex

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