GO:0006122 mitochondrial electron transport, ubiquinol to cytochrome c: Mechanism, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0006122 describes the transfer of electrons from ubiquinol to cytochrome c during oxidative phosphorylation, mediated by complex III of the mitochondrial respiratory chain.
• Complex III is a multisubunit enzyme whose assembly and dimerization are tightly regulated and essential for respiratory function.
• Mutations in complex III subunits, such as CYC1, can cause severe mitochondrial disorders including Leber hereditary optic neuropathy and acute demyelinating syndrome.
• Complex III components such as UQCRC2 and UQCRC1 are implicated in liver injury, tumorigenesis, and cardiac stress tolerance.
• Deficiency in mitochondrial respiratory chain complexes, including complex III, can inhibit lysosomal hydrolysis and impair autophagy.
• CRISPR-based models (knockout, point mutation, knock-in, overexpression) are powerful tools to dissect the causal roles of complex III genes in health and disease.
Description
GO:0006122, mitochondrial electron transport, ubiquinol to cytochrome c, is a biological process that constitutes a central step in oxidative phosphorylation. It is mediated by complex III (also known as the bc1 complex or ubiquinol-cytochrome c oxidoreductase), a multisubunit enzyme embedded in the inner mitochondrial membrane. This process transfers electrons from ubiquinol (reduced coenzyme Q) to cytochrome c, contributing to the proton gradient used for ATP synthesis. Researchers study this term because defects in complex III are linked to a wide range of human pathologies, from mitochondrial myopathies to cancer and neurodegeneration. Understanding the molecular players and regulatory mechanisms of this process is essential for developing targeted therapies and for interpreting genomic variants in mitochondrial disease.
mitochondrial electron transport, ubiquinol to cytochrome c At A Glance
| GO ID | GO:0006122 |
|---|---|
| GO term | mitochondrial electron transport, ubiquinol to cytochrome c |
| Ontology | biological_process |
| Synonym | complex III (ubiquinone to cytochrome c) |
| Major function | Electron transfer from ubiquinol to cytochrome c during oxidative phosphorylation |
| Enzyme complex | Complex III (bc1 complex, ubiquinol-cytochrome c oxidoreductase) |
| Cellular location | Inner mitochondrial membrane |
| Key subunits | CYC1, UQCRC1, UQCRC2, UQCRFS1, UQCRB, UQCRQ, UQCRH, UQCR10, UQCR11 |
| Associated diseases | Mitochondrial complex III deficiency, Leber hereditary optic neuropathy, acute demyelinating syndrome, cancer |
What Is GO:0006122?
According to the Gene Ontology, GO:0006122 is defined as the transfer of electrons from ubiquinol to cytochrome c that occurs during oxidative phosphorylation, mediated by the multisubunit enzyme known as complex III. In simpler terms, it is the step in the mitochondrial respiratory chain where complex III shuttles electrons from ubiquinol to cytochrome c, helping to generate the proton gradient that drives ATP production.
Why Is mitochondrial electron transport, ubiquinol to cytochrome c Important in Cell Biology?
GO:0006122 is essential for cellular energy production and overall mitochondrial function. Complex III is a key component of the electron transport chain, and its dysfunction leads to impaired oxidative phosphorylation, increased reactive oxygen species, and altered cellular metabolism. Clinically, mutations in complex III subunits cause severe mitochondrial disorders, and altered expression of complex III proteins is observed in cancer and metabolic diseases. Therefore, studying this process provides insights into basic mitochondrial biology and offers potential therapeutic targets for a range of human diseases.
• Complex III is a central component of the electron transport chain, required for ATP synthesis.
• Mutations in CYC1 cause complex III deficiency with phenotypes resembling Leber hereditary optic neuropathy or acute demyelinating syndrome.
• UQCRC2 protects against alcohol-induced liver injury by up-regulating mitophagy.
• UQCRC1 promotes tumorigenesis by facilitating p53 degradation, linking complex III to cancer.
• UQCRC1 contributes to cardiac tolerance to acute exhaustive exercise.
• Mitochondrial respiratory chain deficiency, including complex III defects, inhibits lysosomal hydrolysis.
• Complex III assembly and dimerization are tightly regulated processes.
• Autophagy deficiency affects mitochondrial DNA segregation, highlighting crosstalk with complex III function.
• Complex III is a target for drug development against mitochondrial diseases and cancer.
• Understanding complex III biology aids in interpreting genetic variants in mitochondrial disease diagnostics.
What Happens During mitochondrial electron transport, ubiquinol to cytochrome c?
Electron Transfer from Ubiquinol to Cytochrome c
In simple terms: Complex III takes electrons from ubiquinol and hands them to cytochrome c.
The core reaction of GO:0006122 is the transfer of electrons from ubiquinol (reduced coenzyme Q) to cytochrome c. This process is mediated by complex III, which catalyzes the oxidation of ubiquinol and the reduction of cytochrome c. The reaction is coupled to the translocation of protons across the inner mitochondrial membrane, contributing to the proton motive force.
Proton Translocation and Q Cycle
In simple terms: As electrons move, protons are pumped across the membrane, storing energy.
Complex III operates via the Q cycle, a mechanism that allows the transfer of electrons from ubiquinol to cytochrome c while pumping protons across the inner mitochondrial membrane. This proton translocation is essential for generating the electrochemical gradient used by ATP synthase. The Q cycle involves two distinct ubiquinol oxidation sites and a series of electron carriers including the Rieske iron-sulfur protein and cytochromes b and c1.
Assembly and Dimerization of Complex III
In simple terms: Complex III is built from many parts and must pair up to work properly.
Complex III is a multisubunit enzyme that undergoes a coordinated assembly process. Recent studies have shown that dimerization of the bc1 complex occurs at a specific stage during mitochondrial respiratory chain assembly, and this dimerization is required for full activity. The assembly involves the incorporation of catalytic subunits (such as CYC1, UQCRFS1) and structural subunits (such as UQCRC1, UQCRC2) in a stepwise manner.
Regulation by Cellular Stress and Autophagy
In simple terms: Cellular stress and recycling pathways can change how complex III works.
Complex III function is regulated by cellular stress responses. For example, AMPK protects against alcohol-induced liver injury by up-regulating mitophagy through UQCRC2, a complex III subunit. Additionally, mitochondrial respiratory chain deficiency, including complex III defects, can inhibit lysosomal hydrolysis, linking complex III activity to autophagy regulation. Autophagy deficiency itself abolishes liver mitochondrial DNA segregation, indicating crosstalk between complex III and mitochondrial quality control.
Key Genes Involved in GO:0006122 mitochondrial electron transport, ubiquinol to cytochrome c
The following genes encode subunits of complex III or proteins that regulate its function, and they are frequently studied in the context of GO:0006122.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CYC1 | Cytochrome c1 subunit, electron transfer | Mutations cause complex III deficiency and LHON-like phenotypes |
| UQCRC1 | Core protein 1, structural and regulatory | Promotes tumorigenesis via p53 degradation; cardiac exercise tolerance |
| UQCRC2 | Core protein 2, structural and regulatory | Protects against alcohol-induced liver injury via mitophagy |
| UQCRFS1 | Rieske iron-sulfur protein, electron transfer | Essential for complex III catalytic activity |
| UQCRB | Ubiquinone-binding protein | Involved in complex III assembly and function |
| UQCRQ | Ubiquinol-cytochrome c reductase subunit | Complex III assembly and stability |
| UQCRH | Complex III subunit | Structural component of complex III |
| UQCR10 | Complex III subunit | Small subunit contributing to complex III stability |
| UQCR11 | Complex III subunit | Small subunit contributing to complex III stability |
| MT-CYB | Cytochrome b, catalytic core | Mutations cause complex III deficiency and mitochondrial myopathy |
| BCS1L | Chaperone for Rieske protein assembly | Mutations cause complex III assembly defects |
| LYRM7 | Assembly factor for complex III | Required for UQCRFS1 incorporation |
| TTC19 | Assembly factor for complex III | Mutations cause complex III deficiency |
| UQCC1 | Assembly factor for complex III | Involved in early assembly steps |
| UQCC2 | Assembly factor for complex III | Involved in early assembly steps |
| UQCC3 | Assembly factor for complex III | Involved in late assembly steps |
| PET117 | Assembly factor for complex III | Required for cytochrome c oxidase assembly, indirect |
How Is mitochondrial electron transport, ubiquinol to cytochrome c Regulated?
The process of mitochondrial electron transport, ubiquinol to cytochrome c is regulated at multiple levels. Transcriptional regulation of complex III subunits ensures stoichiometric assembly. Post-translational modifications and assembly factors control the maturation of the complex. Cellular stress pathways, such as AMPK signaling, can modulate complex III subunit expression and mitophagy. Additionally, autophagy and lysosomal function influence mitochondrial quality control and complex III activity.
mitochondrial electron transport, ubiquinol to cytochrome c and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CYC1 | Complex III deficiency, LHON, acute demyelinating syndrome | Knockout or point-mutation in cell lines, patient-derived fibroblasts |
| UQCRC1 | Cancer (tumorigenesis via p53 degradation), cardiac exercise tolerance | Knockout and overexpression in cancer cell lines, cardiac-specific KO mice |
| UQCRC2 | Alcohol-induced liver injury, mitophagy regulation | Liver-specific knockout mice, hepatocyte cell lines |
| MT-CYB | Mitochondrial myopathy, complex III deficiency | Cybrid cells with mutant mtDNA, patient-derived cells |
| BCS1L | Complex III assembly defects, GRACILE syndrome | Knockout and knock-in in cell models, yeast complementation |
Mitochondrial Complex III Deficiency and Neurological Disorders
Mutations in complex III subunits, such as CYC1, can cause mitochondrial complex III deficiency, which presents with heterogeneous clinical phenotypes including Leber hereditary optic neuropathy and acute demyelinating syndrome. These disorders highlight the critical role of GO:0006122 in neuronal survival and energy metabolism.
Complex III in Cancer
UQCRC1, a core subunit of complex III, promotes tumorigenesis by facilitating p53 degradation, linking complex III function to cancer cell survival. This suggests that targeting complex III could be a therapeutic strategy in cancers with UQCRC1 overexpression.
Complex III in Liver and Cardiac Stress
UQCRC2 protects against alcohol-induced liver injury by up-regulating mitophagy, indicating a role for complex III in liver stress responses. UQCRC1 contributes to cardiac tolerance to acute exhaustive exercise, showing that complex III function is important for cardiac performance under stress.
Complex III and Autophagy-Lysosomal Crosstalk
Mitochondrial respiratory chain deficiency, including complex III defects, inhibits lysosomal hydrolysis, revealing a link between complex III activity and autophagic flux. Autophagy deficiency also abolishes liver mitochondrial DNA segregation, further connecting complex III to mitochondrial quality control.
From mitochondrial electron transport, ubiquinol to cytochrome c-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of CYC1 impair complex III activity? | CYC1 knockout cell line (e.g., HEK293T) |
| Does a specific point mutation in UQCRC1 affect p53 binding? | UQCRC1 point-mutation knock-in cell line |
| Can overexpression of UQCRC2 protect against alcohol-induced liver injury? | UQCRC2 overexpression in hepatocytes or mouse liver |
| How does tagged UQCRFS1 affect complex III assembly? | Tagged knock-in of UQCRFS1 (e.g., FLAG) in cell lines |
| What is the role of UQCRC1 in cardiac exercise tolerance? | Cardiac-specific UQCRC1 knockout or overexpression mouse model |
| Does autophagy deficiency alter complex III subunit expression? | ATG5 or ATG7 knockout cells, liver-specific autophagy KO mice |
How to Study the mitochondrial electron transport, ubiquinol to cytochrome c Process
| Method | What It Measures | Typical Application |
|---|---|---|
| CRISPR knockout screen | Gene essentiality for respiration | Identify novel complex III regulators |
| Blue native PAGE | Complex III assembly and integrity | Assess assembly defects in patient cells |
| Ubiquinol-cytochrome c reductase assay | Enzymatic activity of complex III | Measure complex III function in tissues |
| Seahorse OCR | Mitochondrial respiration | Evaluate metabolic phenotype of KO cells |
| Immunoblotting | Protein levels of complex III subunits | Validate knockout or overexpression |
| Proteomics (mass spectrometry) | Protein interactions and modifications | Identify novel complex III interactors |
| Mitochondrial imaging | Morphology and localization | Study mitochondrial dynamics |
| Autophagy flux assay | Lysosomal hydrolysis and autophagic flux | Link complex III to autophagy |
CRISPR-Cas9 Knockout Screens
Genome-wide CRISPR knockout screens can identify genes required for complex III function and mitochondrial respiration. Cells with loss of complex III subunits show reduced oxygen consumption and can be selected using metabolic markers.
Proteomic and Biochemical Assays
Blue native PAGE, immunoblotting, and mass spectrometry are used to analyze complex III assembly, subunit composition, and interactions. Enzyme activity assays measure ubiquinol-cytochrome c reductase activity.
Metabolic Flux Analysis
Seahorse extracellular flux analysis measures oxygen consumption rate (OCR) to assess mitochondrial respiration, including complex III-dependent respiration.
Imaging and Mitochondrial Morphology
Fluorescence microscopy with mitochondrial markers (e.g., MitoTracker) and electron microscopy can reveal changes in mitochondrial morphology and cristae structure upon complex III perturbation.
How CRISPR Can Be Used to Study GO:0006122 mitochondrial electron transport, ubiquinol to cytochrome c
Knockout
CRISPR-Cas9 knockout of complex III subunit genes (e.g., CYC1, UQCRC1, UQCRC2) in cell lines abolishes or reduces complex III activity, leading to impaired respiration. These models are used to study the consequences of complex III loss on metabolism, autophagy, and cell survival.
Point Mutation
Point mutations identified in patients (e.g., in CYC1) can be introduced into cell lines using CRISPR prime editing or homology-directed repair to model mitochondrial disease phenotypes and test genotype-phenotype correlations.
Knock-in
Knock-in of tagged versions of complex III subunits (e.g., FLAG-UQCRFS1) allows for affinity purification and proteomic analysis of complex III assembly intermediates and interactors.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression of complex III subunits such as UQCRC2 can be used to test protective effects against stress, e.g., in alcohol-induced liver injury models.
How EDITGENE Supports mitochondrial electron transport, ubiquinol to cytochrome c Research
Researchers studying mitochondrial electron transport, ubiquinol to cytochrome c-related genes often need to determine whether a candidate gene is causally involved in complex III function, disease progression, or therapeutic response. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for mitochondrial electron transport, ubiquinol to cytochrome c research.
Frequently Asked Questions About mitochondrial electron transport, ubiquinol to cytochrome c
What is GO:0006122?
GO:0006122 is the Gene Ontology term for mitochondrial electron transport, ubiquinol to cytochrome c, the process where complex III transfers electrons from ubiquinol to cytochrome c during oxidative phosphorylation.
What genes are involved in mitochondrial electron transport, ubiquinol to cytochrome c?
Key genes include CYC1, UQCRC1, UQCRC2, UQCRFS1, UQCRB, UQCRQ, UQCRH, UQCR10, UQCR11, and MT-CYB, which encode subunits of complex III.
What diseases are associated with complex III dysfunction?
Complex III dysfunction is linked to mitochondrial complex III deficiency, Leber hereditary optic neuropathy, acute demyelinating syndrome, cancer, and liver injury.
How is complex III assembled?
Complex III assembly involves the stepwise incorporation of catalytic and structural subunits, with dimerization occurring at a specific stage during respiratory chain assembly.
What is the role of UQCRC1 in cancer?
UQCRC1 promotes tumorigenesis by facilitating p53 degradation, making it a potential cancer therapeutic target.
How does UQCRC2 protect against liver injury?
UQCRC2 up-regulates mitophagy through AMPK signaling, protecting against alcohol-induced liver injury.
Can CRISPR be used to study complex III genes?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are widely used to study complex III gene function and disease mechanisms.
What methods measure complex III activity?
Ubiquinol-cytochrome c reductase assays, blue native PAGE, and Seahorse OCR are commonly used to measure complex III activity and respiration.
Is complex III involved in autophagy?
Yes, mitochondrial respiratory chain deficiency including complex III defects can inhibit lysosomal hydrolysis, and autophagy deficiency affects mitochondrial DNA segregation.
What model systems are used to study GO:0006122?
Cell lines with CRISPR knockouts, patient-derived fibroblasts, and mouse models are commonly used to study complex III function and dysfunction.
Conclusion
GO:0006122, mitochondrial electron transport, ubiquinol to cytochrome c, is a fundamental biological process carried out by complex III. Its correct function is essential for cellular energy production, and its dysfunction is implicated in a spectrum of human diseases, from mitochondrial disorders to cancer. Continued research using advanced CRISPR models and multi-omics approaches will further elucidate the regulatory mechanisms and therapeutic potential of targeting complex III.
References
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- 3. Fernandez-Mosquera L et al.. 2019. Mitochondrial respiratory chain deficiency inhibits lysosomal hydrolysis.. Autophagy 15(9):1572-1591 PMID: 30917721
- 4. Heidari E et al.. 2021. Defective complex III mitochondrial respiratory chain due to a novel variant in CYC1 gene masquerades acute demyelinating syndrome or Leber hereditary optic neuropathy.. Mitochondrion 60:12-20 PMID: 34252606
- 5. Han Y et al.. 2019. Ubiquinol-cytochrome C reductase core protein II promotes tumorigenesis by facilitating p53 degradation.. EBioMedicine 40:92-105 PMID: 30674441
- 6. Stephan K et al.. 2020. Timing of dimerization of the bc(1) complex during mitochondrial respiratory chain assembly.. Biochim Biophys Acta Bioenerg 1861(5-6):148177 PMID: 32119834
- 7. Yu CA et al.. 1993. Mitochondrial ubiquinol-cytochrome c reductase complex: crystallization and protein: ubiquinone interaction.. J Bioenerg Biomembr 25(3):259-73 PMID: 8394321
- 8. Yi T et al.. 2022. Ubiquinol-cytochrome c reductase core protein 1 contributes to cardiac tolerance to acute exhaustive exercise.. Exp Biol Med (Maywood) 247(2):165-173 PMID: 34648372
