Ferritin Light Chain (FTL)
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<h3 style="margin-top:0; border-bottom:1px solid #ccc;">Ferritin Light Chain</h3>
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<tr><td><b>Gene</b></td><td>[FTL](/genes/ftl)</td></tr>
<tr><td><b>UniProt</b></td><td>[P02792](https://www.uniprot.org/uniprot/P02792)</td></tr>
<tr><td><b>MW</b></td><td>19-21 kDa (subunit)</td></tr>
<tr><td><b>Location</b></td><td>Cytosol, nucleus, mitochondria</td></tr>
<tr><td><b>PDB</b></td><td>[2FFX](https://www.rcsb.org/structure/2FFX)</td></tr>
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<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/depression" style="color:#ef9a9a">Depression</a>, <a href="/wiki/dystonia" style="color:#ef9a9a">Dystonia</a>, <a href="/wiki/leukemia" style="color:#ef9a9a">Leukemia</a></td>
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<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">70 edges</a></td>
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Overview
Mermaid diagram (expand to render)
Ferritin light chain (FTL) is one of two subunits that compose ferritin, the primary iron storage protein in cells. Ferritin forms a 24-subunit spherical shell capable of storing up to 4,500 iron atoms in a bioavailable, non-toxic form. FTL lacks ferroxidase activity (unlike ferritin heavy chain, FTH1) but contributes to iron nucleation and storage stability. FTL mutations cause neurodegeneration with brain iron accumulation (NBIA), and ferritin is increasingly recognized as a therapeutic target in Alzheimer's and Parkinson's diseases.
Structure and Domains
Ferritin is a 24-mer heteropolymer of FTL and FTH1 subunits:
- Four-helix bundle: Each subunit contains four long α-helices (A-D)
- Short fifth helix: C-terminal helix E at subunit interface
- Pore channels: 3-fold and 4-fold channels for iron entry/exit
- Cavity: 8 nm internal cavity for iron mineralization
Subunit Differences
| Feature | FTL | FTH1 |
|---------|-----|------|
| Ferroxidase activity | No | Yes |
| Iron nucleation | Yes | Yes |
| Tissue ratio | Variable (1:1 to 30:1) | Variable |
| Hemosiderin formation | Higher propensity | Lower |
Normal Function
Iron Storage
Ferritin provides safe iron sequestration:
Fe²⁺ entry: Iron enters through 3-fold hydrophilic channels
Oxidation: FTH1 catalyzes Fe²⁺ → Fe³⁺ (ferroxidase)
Nucleation: FTL promotes mineral core formation
Storage: Up to 4,500 Fe atoms as ferrihydriteIron Homeostasis
Ferritin maintains cellular iron balance:
- Buffer: Prevents free iron accumulation
- Reserve: Mobilizable iron source when needed
- Protection: Sequesters iron from Fenton chemistry
Iron-Responsive Regulation
FTL translation is regulated by iron:
- Iron response element (IRE): Stem-loop in 5' UTR
- IRP binding: Low iron → IRP binds IRE → blocks translation
- Iron loading: High iron → IRP dissociates → translation proceeds[@hentze1988]
Role in Neurodegeneration
Neurodegeneration with Brain Iron Accumulation (NBIA)
FTL mutations cause NBIA type 3 (neuroferritinopathy):
- Pathogenic variants: p.Phe167SerfsX26 (460InsA), p.Leu167Pro, others[@curtis2001]
- Mechanism: Mutant FTL disrupts ferritin assembly, reduces iron storage
- Pathology: Iron accumulation in basal ganglia, ferritin aggregates
- Clinical features: Movement disorder, cognitive decline, parkinsonism
Alzheimer's Disease
Ferritin and iron homeostasis are altered in AD:
- Increased ferritin: Elevated ferritin in AD brain and CSF[@connor1995]
- Plaque association: Ferritin colocalizes with amyloid plaques
- Iron dysregulation: AD brains show increased labile iron
- Oxidative stress: Free iron catalyzes [Aβ](/proteins/amyloid-beta)-associated oxidative damage
Ferritin light chain expression may be differentially regulated compared to heavy chain in AD [neurons](/entities/neurons).
Parkinson's Disease
Iron accumulation in substantia nigra involves ferritin:
- Nigral iron: 2-3 fold increase in PD substantia nigra
- Ferritin expression: Altered FTL:FTH1 ratio in PD brain[@friedman1985]
- Dopaminergic neurons: Selective vulnerability may relate to iron handling
- [α-synuclein](/proteins/alpha-synuclein): Interacts with ferritin and affects iron homeostasis
Ferroptosis
Ferritin plays a central role in [ferroptosis](/entities/ferroptosis):
- Iron source: Ferritin degradation (ferritinophagy) releases iron for lipid peroxidation
- NCOA4-mediated: Selective [autophagy](/entities/autophagy) of ferritin via NCOA4 receptor[@mancias2014]
- Protection: High ferritin levels protect against ferroptosis
- Therapeutic: Ferritin stabilizers may inhibit ferroptosis
Therapeutic Targeting
Iron Chelation
Strategies targeting ferritin-associated iron:
| Agent | Mechanism | Status |
|-------|-----------|--------|
| Deferiprone | [BBB](/entities/blood-brain-barrier)-penetrant chelator | Clinical trials (PD, AD) |
| Deferoxamine | Chelator, may mobilize ferritin iron | Limited by BBB penetration |
| Deferasirox | Oral chelator | Research use |
Ferritin Stabilization
Preventing ferritin degradation may protect against ferroptosis:
- NCOA4 inhibitors: Block ferritinophagy
- Chaperone modulators: Enhance ferritin stability
- Iron loading: Promote ferritin expression via IRP release
Ferritin as Biomarker
- CSF ferritin: Elevated in AD and other neurodegenerative diseases
- Serum ferritin: May reflect peripheral iron status
- MRI: Ferritin-weighted imaging detects brain iron accumulation
Genetic Disorders
Neuroferritinopathy
Caused by FTL mutations:
- Inheritance: Autosomal dominant
- Onset: 4th-6th decade
- Features: Chorea, dystonia, rigidity, cognitive decline
- Imaging: Iron accumulation in globus pallidus, putamen, caudate
Hyperferritinemia-Cataract Syndrome
FTL 5' IRE mutations cause:
- Mechanism: Constitutive FTL translation
- Features: Bilateral early-onset cataracts, elevated serum ferritin
- Neurological: Usually normal
Key Interactions
| Partner | Function | Disease Relevance |
|---------|----------|-------------------|
| FTH1 | Heteropolymer formation | Iron storage |
| NCOA4 | Ferritinophagy receptor | Ferroptosis |
| IRP1/IRP2 | IRE-binding regulators | Iron homeostasis |
| Aβ peptide | Plaque-associated | AD iron dysregulation |
| α-synuclein | Aggregation-associated | PD iron homeostasis |
See Also
External Links
- [UniProt: P02792](https://www.uniprot.org/uniprot/P02792)
- [PDB structures](https://www.rcsb.org/search?q=uniprot:P02792)
- [GeneCards: FTL](https://www.genecards.org/cgi-bin/carddisp.pl?gene=FTL)
References
[Hentze et al, A conserved iron-responsive element in the 5' untranslated region of ferritin mRNAs (1988)](https://doi.org/10.1016/0092-8674(88)
[Curtis et al, Mutation in the gene encoding ferritin light polypeptide in dominant adult-onset basal ganglia disease (2001)](https://doi.org/10.1038/ng1107)
[Connor et al, Regional distribution of iron and iron-regulatory proteins in the brain in aging and Alzheimer's disease (1995)](https://pubmed.ncbi.nlm.nih.gov/7775656/)
[Friedman et al, Ferritin particles in the substantia nigra in Parkinson's disease (1985)](https://pubmed.ncbi.nlm.nih.gov/4006792/)
[Mancias et al, Quantitative proteomics reveals NCOA4 as the cargo receptor mediating ferritinophagy (2014)](https://doi.org/10.1038/nature13008)Pathway Diagram
The following diagram shows the key molecular relationships involving Ferritin Light Chain (FTL) discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)