ACAD9 Protein
Introduction
Acad9 Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
--- [@goffart2009]
title: ACAD9 Protein [@tucci2011]
description: Mitochondrial acyl-CoA dehydrogenase involved in fatty acid oxidation and complex I assembly, with critical roles in energy metabolism and neurodevelopment. [@nouws2012]
--- [@schiff2015]
<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" class="infobox-header">ACAD9 Protein</th></tr>
<tr><td class="label">Protein Name</td><td>Acyl-CoA dehydrogenase family member 9</td></tr>
<tr><td class="label">Gene</td><td>[ACAD9](/genes/ACAD9)</td></tr>
<tr><td class="label">UniProt ID</td><td>[Q9H845](https://www.uniprot.org/uniprot/Q9H845)</td></tr>
<tr><td class="label">PDB ID</td><td>3NW7, 5K7P</td></tr>
<tr><td class="label">Molecular Weight</td><td>~68 kDa</td></tr>
<tr><td class="label">Subcellular Localization</td><td>Mitochondrial matrix</td></tr>
<tr><td class="label">Protein Family</td><td>Acyl-CoA dehydrogenase family</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>
Overview
...ACAD9 Protein
Introduction
Acad9 Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
--- [@goffart2009]
title: ACAD9 Protein [@tucci2011]
description: Mitochondrial acyl-CoA dehydrogenase involved in fatty acid oxidation and complex I assembly, with critical roles in energy metabolism and neurodevelopment. [@nouws2012]
--- [@schiff2015]
<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" class="infobox-header">ACAD9 Protein</th></tr>
<tr><td class="label">Protein Name</td><td>Acyl-CoA dehydrogenase family member 9</td></tr>
<tr><td class="label">Gene</td><td>[ACAD9](/genes/ACAD9)</td></tr>
<tr><td class="label">UniProt ID</td><td>[Q9H845](https://www.uniprot.org/uniprot/Q9H845)</td></tr>
<tr><td class="label">PDB ID</td><td>3NW7, 5K7P</td></tr>
<tr><td class="label">Molecular Weight</td><td>~68 kDa</td></tr>
<tr><td class="label">Subcellular Localization</td><td>Mitochondrial matrix</td></tr>
<tr><td class="label">Protein Family</td><td>Acyl-CoA dehydrogenase family</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>
Overview
Acyl-CoA dehydrogenase family member 9 (ACAD9) is a mitochondrial flavoprotein that plays essential roles in fatty acid oxidation and oxidative phosphorylation. Unlike other members of the ACAD family that function in β-oxidation of specific-chain-length fatty acids, ACAD9 has a unique function in facilitating the assembly of mitochondrial complex I (NADH:ubiquinone oxidoreductase), the largest respiratory chain complex [@haack2010]. Mutations in ACAD9 cause a complex I deficiency disorder characterized by cardiomyopathy, encephalopathy, and often early-onset death, highlighting its critical importance in human health [@goffart2009].
Structure
ACAD9 is a homodimeric flavoprotein with characteristic ACAD domain architecture:
| Feature | Description |
|---------|-------------|
| Monomer size | 621 amino acids |
| Quaternary structure | Homodimer (functional unit) |
| Flavin adenine dinucleotide (FAD) | Prosthetic group required for catalytic activity |
| Substrate-binding pocket | Specific for unsaturated C14-C16 acyl-CoAs |
Crystal structures have revealed the molecular basis for ACAD9 substrate specificity and its unique N-terminal extension that mediates complex I assembly [@tucci2011].
Normal Function
Fatty Acid Oxidation
ACAD9 catalyzes the first step in the β-oxidation of fatty acids:
- Substrate specificity: Prefers unsaturated acyl-CoAs with 14-16 carbon chains
- Reaction: Oxidizes acyl-CoA to trans-Δ²-enoyl-CoA, producing FADH₂
- Energy production: FADH₂ enters the electron transfer flavoprotein (ETF) system
Complex I Assembly
The most critical function of ACAD9 is its role in mitochondrial complex I assembly:
- Assembly factor: ACAD9 is essential for the proper assembly of the 45-subunit complex I
- Interaction network: Forms a complex with NDUFAF1 and other assembly factors
- Iron-sulfur cluster binding: Contains iron-sulfur clusters necessary for electron transfer
ACAD9 deficiency impairs complex I activity, disrupting the primary entry point for electrons into the respiratory chain.
Role in Disease
ACAD9 Deficiency (Complex I Deficiency)
Mutations in ACAD9 cause a severe mitochondrial disorder:
Clinical Features:
- Hypertrophic cardiomyopathy (most common)
- Encephalopathy and developmental delay
- Myopathy and exercise intolerance
- Liver dysfunction
- Lactic acidosis
Genetics:
- Autosomal recessive inheritance
- Over 50 pathogenic variants identified
- Variable severity depending on residual enzyme activity
Treatment:
- Supportive care for cardiac and neurological symptoms
- Dietary interventions (low-fat, high-carbohydrate diet)
- CoQ10 supplementation may help some patients
- Avoidance of fasting (increases metabolic stress)
Neurodegenerative Diseases
Alzheimer's Disease
- Complex I dysfunction is observed in AD brains
- ACAD9 expression may be altered in AD
- Mitochondrial dysfunction contributes to [amyloid-beta](/proteins/amyloid-beta) toxicity
Parkinson's Disease
- Complex I deficiency is a hallmark of PD
- ACAD9 variants may modify PD risk
- Mitochondrial dysfunction in dopaminergic [neurons](/entities/neurons)
Leigh Syndrome
- ACAD9 mutations can cause Leigh syndrome
- Characterized by bilateral brainstem lesions
- Severe neurodevelopmental regression
Neurons rely heavily on oxidative phosphorylation:
| Process | Relevance to ACAD9 |
|---------|-------------------|
| Glucose metabolism | Primary neuronal fuel |
| Fatty acid oxidation | Secondary energy source during stress |
| Complex I function | Critical for ATP production |
| Calcium handling | Mitochondria buffer calcium loads |
ACAD9 deficiency leads to impaired ATP production, making neurons particularly vulnerable due to their high energy demands.
Therapeutic Approaches
Gene Therapy
- AAV vectors: Potential for delivering functional ACAD9
- CRISPR-Cas9: Gene editing approaches in development
Pharmacological
- FAD precursors: Riboflavin supplementation may help some patients
- CoQ10: Electron carrier supplementation
- Dichloroacetate: May improve pyruvate metabolism
Dietary Management
- High-carbohydrate diet to reduce fatty acid oxidation burden
- Avoidance of fasting
- Medium-chain triglyceride supplementation (some cases)
Interaction Network
| Partner | Interaction Type | Functional Outcome |
|---------|-----------------|-------------------|
| NDUFAF1 | Direct binding | Complex I assembly scaffold |
| ETFDH | Metabolic | Electron transfer to ETF |
| FAD | Prosthetic group | Catalytic cofactor |
| ND1 | Assembly | Core complex I subunit |
| ND2 | Assembly | Core complex I subunit |
- Knockout mice: Complete knockout is embryonic lethal
- Conditional knockouts: Tissue-specific models for study
- Patient-derived iPSCs: For disease modeling
Background
The study of Acad9 Protein has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
Cross-Links
- [ACAD9 Gene](/acad9-gene)
- Complex I Deficiency
- [Mitochondrial Dysfunction](/mechanisms/mitochondrial-dysfunction)
- Fatty Acid Oxidation
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
See Also
- [ACADVL Protein](/proteins/ACADVL-Protein)
- [MCAD Protein](/proteins/MCAD-Protein)
- [Complex I Proteins](/content/proteins)
- [ETFDH Protein](/proteins/ETFDH-Protein)
- CoQ10 Protein
External Links
- [UniProt: ACAD9](https://www.uniprot.org/uniprot/Q9H845)
- [NCBI Protein: ACAD9](https://www.ncbi.nlm.nih.gov/protein/NP_001138210)
- [GeneCards: ACAD9](https://www.genecards.org/cgi-bin/carddisp.pl?gene=ACAD9)
- [PDB: ACAD9 Structures](https://www.rcsb.org/structure/3NW7)
- [OMIM: ACAD9](https://www.omim.org/entry/611126)
Brain Atlas Resources
- [Allen Human Brain Atlas](https://human.brain-map.org/) — protein expression data
- [Allen Cell Type Atlas](https://celltypes.brain-map.org/) — cell type specific expression
- [BrainSpan Atlas](https://brainspan.org/) — developmental transcriptome
- [Allen Mouse Brain Atlas](https://mouse.brain-map.org/) — mouse brain expression
References
[Haack et al., ACAD9 and complex I deficiency (2010) (2010)](https://pubmed.ncbi.nlm.nih.gov/20140245/))
[Goffart et al., ACAD9 function in mitochondria (2009) (2009)](https://pubmed.ncbi.nlm.nih.gov/19380581/))
[Tucci et al., Crystal structure of ACAD9 (2011) (2011)](https://doi.org/10.1074/jbc.M110.194548))
[Nouws et al., ACAD9 deficiency and mitochondrial disease (2012) (2012)](https://pubmed.ncbi.nlm.nih.gov/22578332/))
[Schiff et al., ACAD9 mutations causing cardiomyopathy (2015) (2015)](https://pubmed.ncbi.nlm.nih.gov/25877300/))