GO:0004174 electron-transferring-flavoprotein dehydrogenase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004174 describes the catalytic activity of electron-transferring-flavoprotein dehydrogenase (ETFDH, also called ETF-QO), which transfers electrons from reduced electron-transfer flavoprotein (ETF) to ubiquinone (coenzyme Q10) in the mitochondrial respiratory chain.
• ETFDH is a nuclear-encoded mitochondrial inner-membrane protein containing a [4Fe-4S] cluster and a flavin adenine dinucleotide (FAD) cofactor that mediate sequential electron transfer.
• Loss-of-function mutations in ETFDH cause multiple acyl-CoA dehydrogenase deficiency (MADD, glutaric aciduria type II), an inherited disorder of fatty acid and amino acid oxidation.
• Mutations in ETFDH are also a major cause of the myopathic form of coenzyme Q10 deficiency, which can be riboflavin-responsive.
• ETFDH activity is central to mitochondrial energy metabolism, linking fatty acid beta-oxidation and branched-chain amino acid catabolism to the ubiquinone pool.
• Research on GO:0004174 uses CRISPR knockout, point-mutation knock-in, overexpression, and biochemical assays to dissect electron transfer, substrate specificity, and disease mechanisms.
Description
Electron-transferring-flavoprotein dehydrogenase (ETFDH; EC 1.5.5.1) is a mitochondrial inner-membrane enzyme that catalyzes the oxidation of reduced electron-transfer flavoprotein (ETF) with concomitant reduction of ubiquinone to ubiquinol. This activity, annotated as GO:0004174, is the terminal step of the electron transfer pathway that collects reducing equivalents from at least nine mitochondrial flavoprotein dehydrogenases involved in fatty acid beta-oxidation and amino acid catabolism. The enzyme is also known as ETF-ubiquinone oxidoreductase (ETF-QO) and contains both a [4Fe-4S] cluster and FAD, which together allow electrons to flow from ETF to ubiquinone. Because it funnels electrons into the respiratory chain, ETFDH is essential for mitochondrial energy production and for maintaining metabolic homeostasis. For researchers, GO:0004174 is a focal point for understanding mitochondrial electron transfer, coenzyme Q10 metabolism, and inherited metabolic disorders. Mutations in ETFDH were first linked to glutaric aciduria type II (multiple acyl-CoA dehydrogenase deficiency, MADD) in the 1980s, and later studies identified ETFDH mutations as a cause of the myopathic form of coenzyme Q10 deficiency. Functional and molecular studies have shown that ETF or ETFDH defects impair fatty acid oxidation and lead to a wide spectrum of clinical presentations, from severe neonatal forms to riboflavin-responsive myopathies. The enzyme's catalytic mechanism, including the role of its redox cofactors and the impact of disease-associated mutations, has been dissected using site-directed mutagenesis and spectroscopic methods. This article provides a research-grade overview of GO:0004174, covering its definition, biological roles, key genes, disease associations, and experimental strategies. It is intended for scientists who study mitochondrial metabolism, inherited metabolic diseases, and the development of CRISPR-based cell models to investigate ETFDH function.
electron-transferring-flavoprotein dehydrogenase activity At A Glance
| GO ID | GO:0004174 |
|---|---|
| GO term | electron-transferring-flavoprotein dehydrogenase activity |
| Ontology | molecular_function |
| Synonym | ETF dehydrogenase activity; ETF-QO activity; electron transfer flavoprotein-ubiquinone oxidoreductase activity; electron-transferring-flavoprotein:ubiquinone oxidoreductase activity |
| Major function | Catalyzes electron transfer from reduced electron-transfer flavoprotein (ETF) to ubiquinone, producing ubiquinol and oxidized ETF. |
| Cofactors | FAD and a [4Fe-4S] cluster. |
| Subcellular location | Mitochondrial inner membrane. |
| Pathway context | Links fatty acid beta-oxidation and amino acid catabolism to the respiratory chain via the ubiquinone pool. |
| Disease relevance | Mutations cause multiple acyl-CoA dehydrogenase deficiency (MADD) and myopathic coenzyme Q10 deficiency. |
What Is GO:0004174?
GO:0004174, electron-transferring-flavoprotein dehydrogenase activity, is defined by the Gene Ontology as the catalysis of the reaction: a ubiquinone + reduced [electron-transfer flavoprotein] = a ubiquinol + H+ + oxidized [electron-transfer flavoprotein]. In other words, the enzyme accepts electrons from reduced electron-transfer flavoprotein (ETF) and transfers them to ubiquinone (coenzyme Q10), converting it to ubiquinol while regenerating oxidized ETF. This activity is also known by synonyms such as ETF dehydrogenase activity, ETF-QO activity, and electron-transfer flavoprotein-ubiquinone oxidoreductase activity.
Why Is electron-transferring-flavoprotein dehydrogenase activity Important in Cell Biology?
GO:0004174 is essential for mitochondrial energy metabolism because it connects the oxidation of fatty acids and several amino acids to the ubiquinone pool of the respiratory chain. Without functional ETFDH, electrons from acyl-CoA dehydrogenases cannot be efficiently transferred to coenzyme Q10, leading to impaired ATP production and accumulation of toxic metabolites. This activity is therefore critical for normal cellular respiration, and its dysfunction is directly linked to inherited metabolic diseases such as multiple acyl-CoA dehydrogenase deficiency and coenzyme Q10 deficiency. Understanding GO:0004174 also informs research on riboflavin metabolism, since some patients with ETFDH mutations respond to riboflavin supplementation.
• ETFDH catalyzes the final step of the electron transfer chain from fatty acid beta-oxidation and amino acid catabolism to ubiquinone.
• It is required for the function of at least nine mitochondrial flavoprotein dehydrogenases.
• Mutations in ETFDH cause multiple acyl-CoA dehydrogenase deficiency (MADD), also known as glutaric aciduria type II.
• ETFDH mutations are a major cause of the myopathic form of coenzyme Q10 deficiency.
• Some ETFDH-related disorders are riboflavin-responsive, linking the enzyme to vitamin B2 metabolism.
• The enzyme contains a [4Fe-4S] cluster and FAD, making it a model for studying electron transfer mechanisms.
• ETFDH activity influences mitochondrial redox balance and cellular energy homeostasis.
• It is a target for understanding the metabolic reprogramming observed in cancer and other diseases.
• Studying GO:0004174 helps interpret genetic variants of uncertain significance in ETFDH.
• ETFDH is used as a biomarker and therapeutic target in inherited mitochondrial myopathies.
What Happens During electron-transferring-flavoprotein dehydrogenase activity?
Electron uptake from reduced ETF
In simple terms: The enzyme grabs electrons from a carrier protein called ETF.
In the first step of the catalytic cycle, electron-transferring-flavoprotein dehydrogenase (ETFDH) binds reduced electron-transfer flavoprotein (ETF), which carries electrons from primary dehydrogenases such as medium-chain acyl-CoA dehydrogenase. The FAD cofactor of ETFDH accepts electrons from the ETF flavin, becoming reduced. This step is the entry point for electrons derived from fatty acid beta-oxidation and amino acid catabolism into the ubiquinone pool.
Intramolecular electron transfer via the [4Fe-4S] cluster
In simple terms: Electrons hop across an iron-sulfur cluster inside the enzyme.
After FAD is reduced, electrons are transferred to the [4Fe-4S] cluster of ETFDH. This cluster acts as a relay, shuttling electrons from the flavin to the ubiquinone-binding site. Mutations that alter the midpoint potential of the [4Fe-4S] cluster can impair catalytic activity, as shown by site-directed mutagenesis studies.
Ubiquinone reduction and ubiquinol formation
In simple terms: The enzyme passes electrons to coenzyme Q10, turning it into ubiquinol.
The final step of the reaction is the reduction of ubiquinone (coenzyme Q10) to ubiquinol. ETFDH transfers two electrons to ubiquinone, releasing protons and regenerating oxidized ETF. Ubiquinol then enters the respiratory chain to reduce complex III, linking ETFDH activity to oxidative phosphorylation.
Regeneration of oxidized ETF
In simple terms: The carrier protein is recycled so it can pick up more electrons.
Upon completion of the catalytic cycle, oxidized ETF is released from ETFDH and can be reused by dehydrogenases. This regeneration is essential for continuous flux through beta-oxidation and amino acid catabolism. Defects in ETFDH therefore lead to accumulation of reduced ETF and impaired substrate oxidation.
Key Genes Involved in GO:0004174 electron-transferring-flavoprotein dehydrogenase activity
The following genes and proteins are directly involved in or functionally associated with electron-transferring-flavoprotein dehydrogenase activity (GO:0004174).
| Gene | Major Role | Research Relevance |
|---|---|---|
| ETFDH | Encodes electron-transferring-flavoprotein dehydrogenase (ETF-QO), the enzyme that catalyzes GO:0004174. | Mutations cause MADD and coenzyme Q10 deficiency; target for functional studies. |
| ETFA | Encodes the alpha subunit of electron-transfer flavoprotein (ETF), the electron donor for ETFDH. | Mutations cause ETF deficiency and MADD; used to study substrate supply to ETFDH. |
| ETFB | Encodes the beta subunit of ETF, which transfers electrons from dehydrogenases to ETFDH. | Defects impair ETFDH activity; relevant for genotype-phenotype studies. |
| ACADM | Medium-chain acyl-CoA dehydrogenase, a primary dehydrogenase that feeds electrons to ETF. | Model for studying electron flux into ETFDH. |
| ACADVL | Very-long-chain acyl-CoA dehydrogenase, donates electrons to ETF. | Relevant for fatty acid oxidation disorders and ETFDH interaction. |
| ACADS | Short-chain acyl-CoA dehydrogenase, contributes electrons to ETF. | Used to assess pathway redundancy and ETFDH dependence. |
| ACADL | Long-chain acyl-CoA dehydrogenase, feeds electrons to ETF. | Target for studying beta-oxidation flux. |
| HADHA | Trifunctional enzyme subunit alpha, involved in fatty acid oxidation and linked to ETF/ETFDH pathway. | Model for mitochondrial energy metabolism. |
| HADHB | Trifunctional enzyme subunit beta, part of beta-oxidation machinery. | Used to study metabolic flux to ETFDH. |
| IVD | Isovaleryl-CoA dehydrogenase, donates electrons to ETF. | Relevant for branched-chain amino acid catabolism. |
| BCKDHA | Branched-chain alpha-keto acid dehydrogenase E1 alpha, upstream of ETF/ETFDH. | Model for amino acid oxidation defects. |
| BCKDHB | Branched-chain alpha-keto acid dehydrogenase E1 beta, contributes to ETF reduction. | Used in metabolic disease research. |
| GCDH | Glutaryl-CoA dehydrogenase, a mitochondrial flavoprotein that reduces ETF. | Model for glutaric aciduria type I and ETF/ETFDH interactions. |
| SLC25A32 | Mitochondrial riboflavin transporter, supplies FAD for ETFDH and other flavoproteins. | Relevant for riboflavin-responsive phenotypes. |
| FLAD1 | FAD synthase, required for FAD cofactor synthesis for ETFDH. | Target for studying cofactor availability. |
| COQ2 | Coenzyme Q10 biosynthesis enzyme, provides ubiquinone substrate for ETFDH. | Model for combined CoQ10 and ETFDH defects. |
| COQ6 | Coenzyme Q10 biosynthesis enzyme, affects ubiquinone pool. | Used to study substrate limitation. |
| NDUFS1 | Complex I subunit, downstream of ubiquinol oxidation. | Model for respiratory chain integration. |
How Is electron-transferring-flavoprotein dehydrogenase activity Regulated?
The activity of ETFDH is regulated at multiple levels. Transcription of ETFDH can be influenced by metabolic signals such as long-chain fatty acids, which regulate energy metabolism genes. Cofactor availability, particularly FAD derived from riboflavin, is critical for ETFDH function, and riboflavin supplementation can restore activity in some patients with ETFDH mutations. The enzyme's activity also depends on the redox state of the ubiquinone pool and the availability of reduced ETF from upstream dehydrogenases. Additionally, post-translational modifications and protein stability may affect ETFDH levels, although specific mechanisms remain to be fully defined.
electron-transferring-flavoprotein dehydrogenase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ETFDH | Multiple acyl-CoA dehydrogenase deficiency (MADD) | CRISPR knockout HEK293T or patient fibroblasts; point-mutation knock-in of common ETFDH variants. |
| ETFDH | Myopathic coenzyme Q10 deficiency | Knock-in of patient mutations in myotubes; overexpression of wild-type ETFDH for rescue. |
| ETFA | ETF deficiency leading to MADD | CRISPR knockout of ETFA in HepG2 cells; biochemical assay of ETF reduction. |
| ETFB | ETF deficiency leading to MADD | Knockout in HeLa cells; complementation with wild-type ETFB. |
| SLC25A32 | Riboflavin-responsive MADD | Knockout in C2C12 myoblasts; riboflavin supplementation studies. |
Multiple acyl-CoA dehydrogenase deficiency (MADD) / Glutaric aciduria type II
Mutations in ETFDH cause multiple acyl-CoA dehydrogenase deficiency (MADD), also known as glutaric aciduria type II. This disorder was first linked to defects in ETF or its dehydrogenase in 1984. Patients present with a wide range of symptoms, including hypoglycemia, metabolic acidosis, muscle weakness, and cardiomyopathy. Functional and molecular studies have shown that ETFDH mutations impair electron transfer from ETF to ubiquinone, leading to accumulation of fatty acids and amino acid metabolites. Some patients respond to riboflavin, highlighting the role of FAD in ETFDH activity.
Myopathic coenzyme Q10 deficiency
Mutations in ETFDH are a major cause of the myopathic form of coenzyme Q10 deficiency, as reported by Gempel et al. in 2007. This condition is characterized by muscle weakness, exercise intolerance, and reduced coenzyme Q10 levels in muscle. The link between ETFDH and coenzyme Q10 deficiency underscores the enzyme's role in maintaining the ubiquinone pool and mitochondrial energy production. Patients may benefit from coenzyme Q10 supplementation, although responses vary.
Riboflavin-responsive metabolic myopathies
A subset of patients with ETFDH mutations exhibit riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency. Zhang et al. (2023) reported hyperhomocysteinemia in patients with riboflavin-responsive MADD, suggesting a complex metabolic interplay. Riboflavin, as a precursor of FAD, can stabilize mutant ETFDH and restore electron transfer activity, making it a potential therapeutic approach.
ETFDH and mitochondrial dysfunction in other diseases
Beyond inherited disorders, altered ETFDH activity may contribute to mitochondrial dysfunction in cancer and metabolic syndrome. Long-chain fatty acids regulate energy metabolism, and ETFDH is part of the metabolic network that can be reprogrammed in disease. However, direct evidence for ETFDH mutations in cancer is limited, and further research is needed.
From electron-transferring-flavoprotein dehydrogenase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of ETFDH impair mitochondrial respiration? | ETFDH knockout in HEK293T or HeLa cells using CRISPR-Cas9. |
| Do patient mutations affect ETFDH catalytic activity? | Point-mutation knock-in of ETFDH variants (e.g., G439R, S545L) in cell lines. |
| Can wild-type ETFDH rescue metabolic defects? | Knock-in of wild-type ETFDH into patient-derived fibroblasts. |
| How does ETFDH interact with ETF and ubiquinone? | Tagged knock-in of ETFDH with FLAG or GFP for co-immunoprecipitation and imaging. |
| What is the effect of ETFDH overexpression on lipid metabolism? | Overexpression of ETFDH in hepatocytes or myotubes. |
| Can CRISPR screening identify modifiers of ETFDH-dependent growth? | Genome-wide CRISPR library screening in ETFDH-mutant cells. |
How to Study the electron-transferring-flavoprotein dehydrogenase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| ETFDH enzyme assay | Catalytic activity using ubiquinone and reduced ETF | Validation of mutant ETFDH function. |
| CRISPR knockout | Loss-of-function effects on metabolism | Studying ETFDH requirement in cell lines. |
| Point-mutation knock-in | Impact of specific patient variants | Genotype-phenotype correlation. |
| Overexpression | Gain-of-function and rescue experiments | Testing therapeutic potential. |
| Metabolomics | Acylcarnitine and organic acid profiles | Diagnosis and mechanism of MADD. |
| Seahorse respirometry | Mitochondrial oxygen consumption | Assessing respiratory chain function. |
| Western blot | Protein expression and stability | Evaluating ETFDH levels. |
| Immunofluorescence | Subcellular localization | Confirming mitochondrial targeting. |
Biochemical assays for ETFDH activity
Enzyme activity of ETFDH can be measured spectrophotometrically by monitoring the reduction of ubiquinone analogs or the oxidation of reduced ETF. These assays use purified enzyme or mitochondrial lysates and are essential for validating the functional impact of mutations. They can be coupled with electron paramagnetic resonance (EPR) to study the [4Fe-4S] cluster.
CRISPR-based genetic models
CRISPR-Cas9 knockout, point-mutation knock-in, and overexpression models allow researchers to dissect the role of ETFDH in cellular metabolism. Knockout cells show impaired fatty acid oxidation and reduced respiration, while knock-in of patient mutations recapitulates disease phenotypes. These models are also useful for testing therapeutic compounds such as riboflavin or coenzyme Q10.
Metabolic profiling and flux analysis
Metabolomics and flux analysis using labeled substrates (e.g., 13C-palmitate) can quantify the impact of ETFDH activity on fatty acid oxidation and amino acid catabolism. Such methods reveal accumulation of acylcarnitines and other metabolites in ETFDH-deficient cells.
Imaging and proteomics
Fluorescence microscopy of tagged ETFDH can reveal its mitochondrial localization and interactions. Proteomics approaches, such as immunoprecipitation coupled with mass spectrometry, can identify binding partners and post-translational modifications of ETFDH.
How CRISPR Can Be Used to Study GO:0004174 electron-transferring-flavoprotein dehydrogenase activity
Knockout
CRISPR-Cas9 knockout of ETFDH in cell lines such as HEK293T or HeLa results in loss of electron-transferring-flavoprotein dehydrogenase activity, leading to impaired fatty acid oxidation and reduced mitochondrial respiration. These knockout models are valuable for studying the metabolic consequences of ETFDH deficiency and for testing rescue strategies.
Point Mutation
Point-mutation knock-in of disease-associated ETFDH variants (e.g., G439R, S545L) allows researchers to study the functional impact of specific mutations on enzyme activity and stability. Such models can reveal genotype-phenotype relationships and inform personalized treatment approaches.
Knock-in
Knock-in of wild-type ETFDH or tagged versions (e.g., FLAG, GFP) enables rescue experiments and interaction studies. Tagged knock-in models facilitate co-immunoprecipitation and imaging to determine ETFDH localization and binding partners.
Overexpression
Overexpression of ETFDH in cell lines or primary cells can enhance electron transfer capacity and may protect against metabolic stress. Overexpression models are used to study the effects of increased ETFDH activity on lipid metabolism and mitochondrial function.
How EDITGENE Supports electron-transferring-flavoprotein dehydrogenase activity Research
Researchers studying electron-transferring-flavoprotein dehydrogenase activity-related genes often need to determine whether a candidate gene is causally involved in mitochondrial metabolism or disease. EDITGENE provides a comprehensive suite of CRISPR-based services to create precise cell models for functional studies of GO:0004174 and its associated pathways.
Contact EDITGENE today to design your custom CRISPR model for electron-transferring-flavoprotein dehydrogenase activity research.
Frequently Asked Questions About electron-transferring-flavoprotein dehydrogenase activity
What is electron-transferring-flavoprotein dehydrogenase activity?
It is the catalytic activity of the enzyme ETFDH (ETF-QO), which transfers electrons from reduced electron-transfer flavoprotein (ETF) to ubiquinone, producing ubiquinol and oxidized ETF. This activity is annotated as GO:0004174.
What genes are involved in electron-transferring-flavoprotein dehydrogenase activity?
The primary gene is ETFDH, which encodes the enzyme. Other genes such as ETFA and ETFB encode the electron donor ETF, while ACADM, ACADVL, and others encode dehydrogenases that feed electrons into the pathway.
What diseases are associated with ETFDH mutations?
Mutations in ETFDH cause multiple acyl-CoA dehydrogenase deficiency (MADD, glutaric aciduria type II) and the myopathic form of coenzyme Q10 deficiency. Some patients respond to riboflavin.
How is ETFDH activity measured in the lab?
ETFDH activity is typically measured using spectrophotometric assays that monitor ubiquinone reduction or ETF oxidation. These assays can be coupled with EPR to study the [4Fe-4S] cluster.
What is the role of FAD in ETFDH?
FAD is a cofactor that accepts electrons from reduced ETF and transfers them to the [4Fe-4S] cluster. Riboflavin, a precursor of FAD, can stabilize mutant ETFDH and restore activity in some patients.
Can CRISPR be used to study ETFDH function?
Yes, CRISPR-Cas9 knockout, point-mutation knock-in, and overexpression models are widely used to study ETFDH function and disease mechanisms.
What is the difference between ETFDH and ETF?
ETF (electron-transfer flavoprotein) is the electron carrier that donates electrons to ETFDH. ETFDH is the dehydrogenase that transfers those electrons to ubiquinone.
Why is ETFDH important for mitochondrial metabolism?
ETFDH links fatty acid beta-oxidation and amino acid catabolism to the respiratory chain by reducing ubiquinone. Without it, electrons cannot efficiently enter the respiratory chain, leading to energy failure.
Are there animal models for ETFDH deficiency?
Yes, knockout mouse models of ETFDH exist and recapitulate aspects of MADD, including lipid accumulation and metabolic acidosis. These models are used to test therapies.
What is the clinical presentation of ETFDH deficiency?
Symptoms include muscle weakness, exercise intolerance, hypoglycemia, metabolic acidosis, and cardiomyopathy. The severity varies from neonatal to adult-onset forms.
Conclusion
GO:0004174, electron-transferring-flavoprotein dehydrogenase activity, is a critical mitochondrial function that connects fatty acid and amino acid oxidation to the respiratory chain. The enzyme ETFDH, encoded by ETFDH, catalyzes the transfer of electrons from reduced ETF to ubiquinone, and its dysfunction causes severe metabolic disorders such as MADD and coenzyme Q10 deficiency. Understanding the molecular mechanism, regulation, and disease relevance of this activity is essential for developing targeted therapies. Researchers can leverage CRISPR-based cell models, biochemical assays, and metabolic profiling to dissect ETFDH function and identify therapeutic strategies. EDITGENE provides comprehensive services to support these studies, from knockout and knock-in models to library screening and bioinformatics analysis.
References
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