abcd1-protein

ABCD1 Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">abcd1-protein</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[ABCD1](/genes/abcd1)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[P33897](https://www.uniprot.org/uniprot/P33897)</td>
</tr>
<tr>
<td class="label">PDB Structures</td>
<td>6BVO, 6VX4</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~66 kDa</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Peroxisomal membrane</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>ABC transporter family D</td>
</tr>
<tr>
<td class="label">Length</td>
<td>660 amino acids</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/inflammation" style="color:#ef9a9a">Inflammation</a>, <a href="/wiki/ms" style="color:#ef9a9a">Ms</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodegeneration</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">35 edges</a></td>
</tr>
</table>

Overview

ABCD1 Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">abcd1-protein</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[ABCD1](/genes/abcd1)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[P33897](https://www.uniprot.org/uniprot/P33897)</td>
</tr>
<tr>
<td class="label">PDB Structures</td>
<td>6BVO, 6VX4</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~66 kDa</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Peroxisomal membrane</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>ABC transporter family D</td>
</tr>
<tr>
<td class="label">Length</td>
<td>660 amino acids</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/inflammation" style="color:#ef9a9a">Inflammation</a>, <a href="/wiki/ms" style="color:#ef9a9a">Ms</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodegeneration</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">35 edges</a></td>
</tr>
</table>

Overview

ABCD1 (ATP-binding cassette subfamily D member 1) is a peroxisomal membrane transporter protein essential for the import of very long-chain fatty acids (VLCFAs) into peroxisomes for β-oxidation[@mosser1993]. Located in the peroxisomal membrane, ABCD1 functions as a half-transporter that forms homodimers to create a functional transporter complex. Mutations in ABCD1 cause [X-linked adrenoleukodystrophy](/diseases/x-linked-adrenoleukodystrophy) (X-ALD), one of the most common peroxisomal disorders, characterized by progressive cerebral demyelination and adrenal insufficiency.

X-ALD affects approximately 1 in 21,000 males, making it the most common inherited peroxisomal disorder. The disease presents with a wide spectrum of phenotypes, from childhood cerebral ALD to adult-onset adrenomyelopathy, reflecting the complex pathophysiology of VLCFA accumulation in the brain and adrenal glands.

Protein Infobox

Structure

ABCD1 is a peroxisomal ATP-binding cassette transporter with characteristic domain architecture[@kemp2001]:

Transmembrane Domains

• Six transmembrane helices: Form the translocation pore
• Peroxisomal membrane topology: N- and C-termini face the cytosol
• Substrate binding pocket: Located within the membrane

Nucleotide-Binding Domain (NBD)

• N-terminal NBD: Binds and hydrolyzes ATP
• Walker A motif: Phosphate-binding loop (P-loop)
• Walker B motif: Coordinates Mg²⁺ ion
• ABC signature (C-loop): LSGGQ motif essential for function

Dimerization

• Half-transporter: Functions as homodimer
• Dimerization domain: C-terminal interactions
• Functional complex: Two ABCD1 monomers form one transporter

Comparison with Other ABCD Family Members

• ABCD2: Adipose-specific, partially compensates for ABCD1 loss
• ABCD3: Broader substrate specificity
• ABCD4: Lysosomal/peroxisomal localization

Normal Function

Very Long-Chain Fatty Acid Import

Substrate Specificity

• VLCFAs: C24-C26 fatty acids
• Very long-chain monocarboxylic acids
• Bile acid intermediates

Transport Mechanism

• Import: VLCFAs transported into peroxisome matrix
• β-oxidation: Mitochondrial/ peroxisomal breakdown
• Chain shortening: Produces medium-chain fatty acids

Peroxisomal Function

• Lipid metabolism: Essential for peroxisomal β-oxidation
• Very long-chain fatty acid catabolism
• Plasmalogen synthesis support
• Bile acid synthesis

Cellular Homeostasis

• Prevents VLCFA accumulation in cellular membranes
• Maintains membrane lipid composition
• Supports myelin maintenance

Role in Disease

X-Linked Adrenoleukodystrophy (X-ALD)

ABCD1 deficiency causes X-ALD through VLCFA accumulation[@steinberg2009]:

Pathogenesis

• VLCFA accumulation: In brain white matter, adrenal cortex
• Inflammatory demyelination: Progressive cerebral disease
• Adrenal insufficiency: VLCFA toxicity to adrenocortical cells
• Oxidative stress: Mitochondrial dysfunction

Clinical Phenotypes

Childhood Cerebral ALD (CCALD)

• Age of onset: 3-10 years
• Progressive behavioral/cognitive decline
• Motor dysfunction
• Visual impairment
• Fatal within 2-4 years without intervention

• Adult-onset (20-40 years)
• Progressive spinal cord disease
• Adrenal insufficiency
• Variable cerebral involvement

• Adrenal insufficiency only
• May progress to cerebral disease
• Requires hormone replacement

Adrenal Dysfunction

• VLCFA accumulation in adrenal cortex
• Cortical cell degeneration
• Reduced steroid hormone production
• Requires glucocorticoid replacement

Peroxisomal Disorders

ABCD1 mutations are central to peroxisomal biogenesis disorders:

• Zellweger spectrum: Peroxisome biogenesis defects
• Neonatal adrenoleukodystrophy
• Infantile Refsum disease

Neurological Manifestations

The neurological symptoms of X-ALD include:

• Cognitive decline: Memory, executive function
• Motor dysfunction: Paraparesis, ataxia
• Visual loss: Optic nerve involvement
• Hearing loss: Sensorineural
• Peripheral neuropathy

Therapeutic Targeting

Lorenzo's Oil

A dietary intervention to reduce VLCFA levels[@kim2019]:

• Composition: 4:1 oleic acid to erucic acid
• Mechanism: Reduces VLCFA absorption
• Efficacy: Normalizes VLCFA levels in most patients
• Limitations: Does not reverse established disease

Gene Therapy

AAV-mediated ABCD1 delivery shows promise[@vezina2019]:

• Lenti-D (autologous): Hematopoietic stem cell gene therapy
• Skysona (elivaldogene autotemcel): FDA-approved for CALD
• AAV vectors: Direct CNS delivery in development

Hematopoietic Stem Cell Transplantation

• Donor cells: Produce functional protein
• Stabilizes disease: In early-stage CALD
• Risks: Graft-versus-host disease, mortality

PPAR Agonists

• Increase peroxisome number: May partially compensate
• Fenofibrate: Being investigated
• Limited efficacy: As monotherapy

Adrenal Hormone Replacement

• Glucocorticoids: Hydrocortisone
• Mineralocorticoids: Fludrocortisone
• Stress dosing: Required for illness/surgery

Key Publications

Cross-Links

• [ABCD1 Gene](/genes/abcd1) - Gene page
• [X-Linked Adrenoleukodystrophy](/diseases/x-linked-adrenoleukodystrophy) - Disease
• [Peroxisome Function](/mechanisms/peroxisome-function) - Pathway
• [VLCFA Metabolism](/mechanisms/vlcfa-metabolism) - Pathway
• [White Matter Disorders](/diseases/white-matter-disorders) - Disease category

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

See Also

• [ABCD1 Gene](/genes/abcd1)
• [X-Linked Adrenoleukodystrophy](/diseases/x-linked-adrenoleukodystrophy)
• [Peroxisomes](/mechanisms/peroxisome-function)
• [White Matter Disorders](/diseases/white-matter-disorders)
• [Oligodendrocyte](/cell-types/oligodendrocyte)
• [VLCFA Metabolism](/mechanisms/vlcfa-metabolism)

External Links

• [UniProt: P33897](https://www.uniprot.org/uniprot/P33897)
• [GeneCards: ABCD1](https://www.genecards.org/cgi-bin/carddisp.pl?gene=ABCD1)
• [X-ALD Foundation](https://www.x-ald.org/)
• [ALD Connect](https://aldconnect.org/)