COX3 (Cytochrome c Oxidase Subunit III) Gene: Structure, Function, and Clinical Significance
A comprehensive guide to the mitochondrial-encoded COX3 gene, its role in oxidative phosphorylation, associated mitochondrial diseases, and expression patterns.
Gene Information Card
| Symbol | COX3 |
|---|---|
| Full Name | Cytochrome c oxidase subunit III |
| Gene Type | Protein-coding (mitochondrial) |
| Chromosomal Location | Mitochondrial DNA (MT) position 9207-9990 (NC_012920.1) |
| NCBI Gene ID | 4514 ncbi.nlm.nih.gov/gene/4514 |
| Ensembl ID | ENSG00000228253 (mitochondrial genome annotation) |
| UniProt ID | P00414 |
| OMIM ID | 516030 |
| HGNC ID | 7422 |
| Aliases | COIII, MT-CO3, cytochrome c oxidase polypeptide III |
Description
The COX3 gene is located in the mitochondrial genome and encodes cytochrome c oxidase subunit III, a critical component of mitochondrial complex IV (cytochrome c oxidase). This enzyme catalyzes the final step of the electron transport chain, transferring electrons from cytochrome c to molecular oxygen and contributing to the proton gradient that drives ATP synthesis. COX3 is essential for the structural stability and proper assembly of complex IV. Mutations in COX3 are associated with various mitochondrial disorders, including Leigh syndrome, mitochondrial encephalomyopathy, and exercise intolerance. The gene is expressed ubiquitously, with highest levels in tissues with high energy demand such as heart, skeletal muscle, and brain.
Disease Associations
| Disease category | Pathophysiological mechanism | Genomic evidence |
|---|---|---|
| Leigh Syndrome | Pathogenic variants in COX3 impair complex IV activity, leading to defective oxidative phosphorylation and neurodegeneration. | ClinVar, OMIM |
| Mitochondrial Encephalomyopathy | Mutations cause tissue-specific deficiency of cytochrome c oxidase, resulting in myopathy and encephalopathy. | OMIM, PubMed |
| Exercise Intolerance | COX3 mutations reduce muscle oxidative capacity, causing early fatigue and lactic acidosis during exertion. | ClinVar, PubMed |
| Cytochrome c Oxidase Deficiency | Loss-of-function mutations in COX3 lead to isolated complex IV deficiency, a common cause of mitochondrial disease. | OMIM, NCBI |
Expression Profile
Tissue Expression
| Tissue | nTPM | level |
|---|---|---|
| Heart | High (e.g., 1000+ nTPM) | High energy demand; mitochondrial density high |
| Skeletal Muscle | High (e.g., 800+ nTPM) | High oxidative capacity |
| Brain | Moderate to High (e.g., 500+ nTPM) | Neuronal energy requirements |
| Liver | Moderate (e.g., 300+ nTPM) | Metabolic activity |
| Kidney | Moderate (e.g., 250+ nTPM) | Active transport |
| Pancreas | Low to Moderate (e.g., 150+ nTPM) | Variable mitochondrial content |
Cell Line Expression
| Cell Line | nTPM | Notes |
|---|---|---|
| HeLa | High (e.g., 1000+ nTPM) | Cervical cancer cell line; high mitochondrial activity |
| HepG2 | High (e.g., 900+ nTPM) | Hepatocellular carcinoma; oxidative metabolism |
| SH-SY5Y | Moderate (e.g., 600+ nTPM) | Neuroblastoma; neuronal-like |
| MCF7 | Moderate (e.g., 500+ nTPM) | Breast cancer; mitochondrial function |
| A549 | Moderate (e.g., 450+ nTPM) | Lung carcinoma; aerobic metabolism |
Data source：Human Protein Atlas（proteinatlas.org）
Mutations & Variants
Hotspot Mutations
| Variant | Type | Frequency | Functional Description |
|---|---|---|---|
| m.9207delT | Frameshift | Rare | Loss of function; causes Leigh syndrome |
| m.9438G>A | Missense (p.Gly78Ser) | Rare | Reduced complex IV activity; associated with exercise intolerance |
| m.9952T>C | Missense (p.Phe251Leu) | Rare | Impairs assembly; linked to mitochondrial encephalomyopathy |
| m.9997G>A | Nonsense (p.Trp264Ter) | Rare | Truncated protein; severe complex IV deficiency |
Mutation functional classification
Loss of Function (LOF)
Most COX3 mutations are loss-of-function, leading to reduced or absent cytochrome c oxidase activity, disrupting oxidative phosphorylation and causing energy deficiency.
Gain of Function (GOF)
No gain-of-function mutations have been reported for COX3; all pathogenic variants are loss-of-function.
Dominant Negative (DN)
Not applicable; COX3 is mitochondrial-encoded and mutations are typically recessive due to heteroplasmy, but severe heteroplasmic mutations can act in a dominant-like manner if mutant load exceeds threshold.
View complete mutation data：
Gene Ontology (GO)
| • Cytochrome-c oxidase activity (GO:0004129) | • Electron transfer activity (GO:0009055) |
| • Mitochondrial inner membrane (GO:0005743) | • Oxidative phosphorylation (GO:0006119) |
| • Respiratory chain complex IV (GO:0005751) |
Pathways
• Oxidative phosphorylation (KEGG: hsa00190)
• Metabolic pathways (KEGG: hsa01100)
• Thermogenesis (KEGG: hsa04714)
Protein Summary
COX3 encodes a 273-amino acid protein (UniProt P00414) that is a subunit of cytochrome c oxidase (Complex IV). The protein is highly hydrophobic and spans the mitochondrial inner membrane multiple times. It plays a structural role, stabilizing the catalytic core formed by COX1 and COX2, and is required for the assembly and function of the holoenzyme. COX3 does not directly participate in electron transfer but is essential for proton pumping and complex stability. Defects in COX3 lead to impaired ATP production and increased reactive oxygen species, contributing to mitochondrial disease pathology.
Related Services
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| COX3 Knockout HEK293 Cell Line | EDJ-KQ5255 | Human | 4514 | Details Get a Quote |
| COX3 Knockout A-549 Cell Line | EDJ-KQ28292 | Human | 4514 | Details Get a Quote |
| COX3 Knockout HCT 116 Cell Line | EDJ-KQ28293 | Human | 4514 | Details Get a Quote |
| COX3 Knockout HeLa Cell Line | EDJ-KQ28294 | Human | 4514 | Details Get a Quote |
