Dataset Information

Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX.

ABSTRACT: 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.

SUBMITTER: Feng X

PROVIDER: S-EPMC7812768 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX.

Feng Xiang X Schut Gerrit J GJ Lipscomb Gina L GL Li Huilin H Adams Michael W W MWW Adams Michael W W MWW

Proceedings of the National Academy of Sciences of the United States of America 20210101 2

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 ...[more]

PMID: 33372143

Similar Datasets

Project description:Electron transfer bifurcation enables biological systems to drive unfavourable (endergonic) electron transfer by coupling it to favourable (exergonic) transfer of a second electron. In electron transfer flavoproteins (ETFs), a domain-scale conformational change is believed to sever the favourable pathway after a single electron has used it, thereby preventing the energy dissipation that would accompany exergonic transfer of the second electron. To understand the conformation change that participates in turnover, we have deployed small-angle neutron scattering (SANS) and computational techniques to characterize the bifurcating ETF from Acidaminococcus fermentans (AfeETF). SANS data reveal an overall radius of gyration (R g) of 30.1 ± 0.2 Å and a maximum dimension (D max) of 100 Å for oxidized AfeETF. These measurements are 4 Å and 30 Å larger, respectively, than those of any published bifurcating ETF structure. Thus, we find that none of the reported ETF structures can explain the observed scattering, nor can any individual conformation generated by either of our molecular dynamics protocols. To optimize ensembles best able to explain the SANS data, we adapted a genetic algorithm. Successful ensembles contained a compact conformation comparable to one of the crystallographically documented conformations, accompanied by a much more extended one, and these two conformations sufficed to account for the data. The extended conformations identified all have R gs at least 4 Å larger than those of any currently published ETF structures. However, they are strongly populated, constituting 20% of the population of reduced ETF and over 50% of the population of oxidized AfeETF. Thus, the published (compact) structures provide a seriously incomplete picture of the conformation of AfeETF in solution. Moreover, because the composition of the conformational ensemble changes upon reduction of AfeETF's flavins, interconversion of the conformations may contribute to turnover. We propose that the extended conformations can provide energetically accessible paths for rapid interconversion of the open and closed compact conformations that are believed essential at alternating points in turnover.

Dataset Information

Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX.

Publications

Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets