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Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX
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Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX
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Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX
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Journal Article
Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX
2021
Overview
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 (E°′ ∼−450 mV) using NADH (E°′ −320 mV) as the electron donor by coupling this reaction to the exergonic reduction of menaquinone (E°′ −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.
Publisher
National Academy of Sciences,Proceedings of the National Academy of Sciences
Subject
Bacterial Proteins - metabolism
/ Cryoelectron Microscopy - methods
/ Dimers
/ Electron-Transferring Flavoproteins - metabolism
/ Flavin
/ Iron-Sulfur Proteins - metabolism
/ NADH
/ Nicotinamide adenine dinucleotide
/ Nitrogen Fixation - physiology
/ Pyrococcus furiosus - metabolism
/ Quinone Reductases - metabolism
/ Quinone Reductases - physiology
/ Quinone Reductases - ultrastructure
/ Quinones
