Electron-transferring-flavoprotein dehydrogenase

 

Electron transfer flavoprotein-ubiquinone oxidoreductase is oxidised by the diffusible ubiquinone. The ubiquinol product relays electrons onto complex III. The enzyme links electrons from the oxidations of fatty acids to the mitochondrial respiratory chain.

 

Reference Protein and Structure

Sequence
P55931 UniProt (1.5.5.1) IPR023753 (Sequence Homologues) (PDB Homologues)
Biological species
Sus scrofa (pig) Uniprot
PDB
2gmh - Structure of Porcine Electron Transfer Flavoprotein-Ubiquinone Oxidoreductase in Complexed with Ubiquinone (2.5 Å) PDBe PDBsum 2gmh
Catalytic CATH Domains
3.50.50.60 CATHdb 3.30.70.20 CATHdb 3.30.9.90 CATHdb (see all for 2gmh)
Cofactors
Fadh2(2-) (1), Tetra-mu3-sulfido-tetrairon (1) Metal MACiE
Click To Show Structure

Enzyme Reaction (EC:1.5.5.1)

FADH2(2-)
CHEBI:58307ChEBI
+
ubiquinones
CHEBI:16389ChEBI
→
hydron
CHEBI:15378ChEBI
+
ubiquinol
CHEBI:17976ChEBI
+
FAD(3-)
CHEBI:57692ChEBI
Alternative enzyme names: ETF-QO, ETF:ubiquinone oxidoreductase, Electron transfer flavoprotein Q oxidoreductase, Electron transfer flavoprotein dehydrogenase, Electron transfer flavoprotein reductase, Electron transfer flavoprotein-ubiquinone oxidoreductase, ETF-ubiquinone oxidoreductase, ETF dehydrogenase,

Enzyme Mechanism

Introduction

The reduced electron transfer flavoprotein delivers electron to the FAD cofactor via the iron sulfur cluster. The oxidised electron transfer flavoprotein donates a proton to the FAD cofactor. The one electron oxidised electron transfer flavoprotein donates a second electron to the iron sulfur cluster, reducing its overall charge from +2 to +1. The semiquinone FAD intermediate reduces the bound ubiquinone substrate. The electron held by the iron sulfur cluster is now transferred to the FAD cofactor. The oxidised electron transfer flavoprotein donates a proton to the FAD cofactor. FAD now donates a second reducing equivalent to the ubiquinone, forming the quinol product and regenerating the cofactor.

Catalytic Residues Roles

UniProt PDB* (2gmh)
Cys589 (main-C) Cys556A (main-C) Forms part of the electron relay chain from the electron transfer protein to the FAD of the active site. single electron relay, single electron acceptor, single electron donor
Thr400, Ser115 Thr367A, Ser82A Help stabilise the reactive intermediates formed during the course of the reaction. electrostatic stabiliser
Arg364 Arg331A Forms part of the electron relay from the electron transfer protein to the FAD in the active site. single electron relay, hydrogen bond acceptor, hydrogen bond donor, activator, single electron acceptor, single electron donor
Cys586, Cys592, Cys561, Cys589 Cys553A, Cys559A, Cys528A, Cys556A Binds the iron-sulfur cluster. attractive charge-charge interaction, activator, metal ligand, electrostatic stabiliser
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

electron transfer, redox reaction, overall reactant used, cofactor used, intermediate formation, electron relay, proton transfer, native state of cofactor regenerated, intermediate terminated, overall product formed, inferred reaction step, intermediate collapse, native state of enzyme regenerated

References

  1. Zhang J et al. (2006), Proc Natl Acad Sci U S A, 103, 16212-16217. Structure of electron transfer flavoprotein-ubiquinone oxidoreductase and electron transfer to the mitochondrial ubiquinone pool. DOI:10.1073/pnas.0604567103. PMID:17050691.
  2. Swanson MA et al. (2008), Biochemistry, 47, 8894-8901. The Iron−Sulfur Cluster of Electron Transfer Flavoprotein−Ubiquinone Oxidoreductase Is the Electron Acceptor for Electron Transfer Flavoprotein†. DOI:10.1021/bi800507p. PMID:18672901.

Step 1. The reduced electron transfer flavoprotein delivers electron to the FAD cofactor via the iron sulfur cluster. Mutagenesis and kinetic calculations have shown the electron to relay through the Fe4S4 cluster before reaching the FAD cofactor, rather than being directly donated to the flavin [PMID:18672901]. The electron is relayed to FAD from the iron sulfur cluster through interactions between the close proximity cabronyl of the metal ligand Cys556 and the carbonyl of Arg331 [PMID:17050691].

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Catalytic Residues Roles

Residue Roles
Arg331A activator, hydrogen bond donor, hydrogen bond acceptor
Cys556A activator, attractive charge-charge interaction, metal ligand, hydrogen bond acceptor
Cys528A activator, attractive charge-charge interaction, metal ligand
Cys559A activator, attractive charge-charge interaction, metal ligand
Cys553A activator, attractive charge-charge interaction, metal ligand
Ser82A hydrogen bond donor, electrostatic stabiliser
Arg331A single electron acceptor
Thr367A electrostatic stabiliser
Arg331A single electron relay
Cys556A (main-C) single electron relay, single electron donor, single electron acceptor
Arg331A single electron donor

Chemical Components

electron transfer, redox reaction, overall reactant used, cofactor used, intermediate formation, electron relay

Step 2. The oxidised electron transfer flavoprotein donates a proton to the FAD cofactor

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Catalytic Residues Roles

Residue Roles
Arg331A hydrogen bond donor, hydrogen bond acceptor
Cys556A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser, hydrogen bond acceptor
Cys528A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys559A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys553A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Ser82A hydrogen bond donor
Thr367A electrostatic stabiliser

Chemical Components

proton transfer, cofactor used, overall reactant used, intermediate formation

Step 3. The one electron oxidised electron transfer flavoprotein donates a second electron to the iron sulfur cluster. On the addition of a second electron from the ET-transport flavin, both the flavin cofactor and Fe-S cluster are in a single electron reduced states, i.e a semi-quinone and +1 state, respecitively [PMID:17050691].

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Catalytic Residues Roles

Residue Roles
Arg331A hydrogen bond donor, hydrogen bond acceptor
Cys556A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys528A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys559A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys553A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Ser82A hydrogen bond donor
Thr367A electrostatic stabiliser

Chemical Components

electron transfer, redox reaction, cofactor used, intermediate formation

Step 4. The semiquinone FAD intermediate reduces the bound ubiquinone substrate.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Arg331A hydrogen bond donor, hydrogen bond acceptor
Cys556A activator, metal ligand, attractive charge-charge interaction, electrostatic stabiliser
Cys528A activator, metal ligand, attractive charge-charge interaction, electrostatic stabiliser
Cys559A activator, metal ligand, attractive charge-charge interaction, electrostatic stabiliser
Cys553A activator, metal ligand, attractive charge-charge interaction, electrostatic stabiliser
Ser82A hydrogen bond donor, electrostatic stabiliser
Thr367A electrostatic stabiliser

Chemical Components

electron transfer, proton transfer, redox reaction, overall reactant used, native state of cofactor regenerated, intermediate formation

Step 5. A second electron is donated from the Fe4S4 cluster to the FAD. The centres are coupled by the interaction between the Cys556 carbonyl and Arg331 [PMID:18672901].

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Arg331A activator, hydrogen bond donor, hydrogen bond acceptor
Cys556A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys528A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys559A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys553A activator, electrostatic stabiliser, attractive charge-charge interaction, metal ligand
Ser82A electrostatic stabiliser, hydrogen bond acceptor
Arg331A single electron acceptor
Thr367A electrostatic stabiliser
Arg331A single electron relay
Cys556A (main-C) single electron donor, single electron relay, single electron acceptor
Arg331A single electron donor

Chemical Components

electron transfer, cofactor used, intermediate terminated, electron relay, native state of cofactor regenerated

Step 6. The oxidised electron transfer flavoprotein donates a proton to the FAD cofactor

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Arg331A hydrogen bond donor, hydrogen bond acceptor
Cys556A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys528A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys559A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys553A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Ser82A hydrogen bond donor
Thr367A electrostatic stabiliser

Chemical Components

proton transfer, cofactor used, overall reactant used, intermediate formation, overall product formed, inferred reaction step

Step 7. FAD now donates a second reducing equivalent to the ubiquinone, forming the quinol product and regenerating the cofactor.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Arg331A hydrogen bond donor, hydrogen bond acceptor
Cys556A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys528A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys559A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Cys553A activator, attractive charge-charge interaction, metal ligand, electrostatic stabiliser
Ser82A hydrogen bond donor
Thr367A electrostatic stabiliser

Chemical Components

proton transfer, electron transfer, redox reaction, intermediate collapse, native state of cofactor regenerated, overall product formed, native state of enzyme regenerated, inferred reaction step
Download: Image, Marvin File

Step 1. The reduced electron transfer flavoprotein delivers electron to the FAD cofactor via the iron sulfur cluster. Mutagenesis and kinetic calculations have shown the electron to relay through the Fe4S4 cluster before reaching the FAD cofactor, rather than being directly donated to the flavin [PMID:18672901]. The electron is relayed to FAD from the iron sulfur cluster through interactions between the close proximity cabronyl of the metal ligand Cys556 and the carbonyl of Arg331 [PMID:17050691].

Step 2. The oxidised electron transfer flavoprotein donates a proton to the FAD cofactor

Step 3. The one electron oxidised electron transfer flavoprotein donates a second electron to the iron sulfur cluster. On the addition of a second electron from the ET-transport flavin, both the flavin cofactor and Fe-S cluster are in a single electron reduced states, i.e a semi-quinone and +1 state, respecitively [PMID:17050691].

Step 4. The semiquinone FAD intermediate reduces the bound ubiquinone substrate.

Step 5. A second electron is donated from the Fe4S4 cluster to the FAD. The centres are coupled by the interaction between the Cys556 carbonyl and Arg331 [PMID:18672901].

Step 6. The oxidised electron transfer flavoprotein donates a proton to the FAD cofactor

Step 7. FAD now donates a second reducing equivalent to the ubiquinone, forming the quinol product and regenerating the cofactor.

Products.

Contributors

Sophie T. Williams, Gemma L. Holliday