Cystinosin (CTNS Protein)

Migration, Crosslink

📖

Cystinosin (CTNS Protein)

active

wiki page Created: 2026-04-02T07:19:12 By: crosslink-migration Quality: 50% ✓ SciDEX ID: wiki-proteins-ctns-protein

📖 Wiki Page

protein888 wordssynced 2026-04-02

Cystinosin (CTNS Protein)

Introduction

Cystinosin (encoded by the [CTNS gene](/genes/ctns)) is a lysosomal membrane transporter protein critical for cystine efflux from lysosomes. Deficiency causes cystinosis, a lysosomal storage disorder with progressive neurological involvement.

Overview

Cystinosin is a 367-amino acid polytopic membrane protein localized to the lysosomal membrane, where it functions as an H⁺-driven cystine transporter[1]. It belongs to the PQ-loop family of transporters and contains seven predicted transmembrane domains. Cystinosin is essential for preventing the toxic accumulation of cystine crystals within lysosomes and plays broader roles in [autophagy](/mechanisms/autophagy-lysosomal-pathway-parkinsons), mTORC1 signaling, and lysosomal homeostasis[2]. [@festa2018]

<div class="infobox infobox-protein"> [@kalatzis2001]

| | | [@ivanova2015]
|---|---| [@trauner2010]
| Protein Name | Cystinosin | [@bellomo2018]
| Gene | [CTNS](/genes/ctns) |
| UniProt ID | [O60931](https://www.uniprot.org/uniprot/O60931) |
| Molecular Weight | ~42 kDa (predicted), ~55 kDa (glycosylated) |
| Subcellular Localization | Lysosomal membrane |
| Function | H⁺-driven lysosomal cystine transporter |
| PDB Structures | [AlphaFold: AF-O60931](https://alphafold.ebi.ac.uk/entry/O60931) |

</div>

Structure

Domain Architecture

Cystinosin has a distinctive topology[1]:

...

Cystinosin (CTNS Protein)

Introduction

Cystinosin (encoded by the [CTNS gene](/genes/ctns)) is a lysosomal membrane transporter protein critical for cystine efflux from lysosomes. Deficiency causes cystinosis, a lysosomal storage disorder with progressive neurological involvement.

Overview

Cystinosin is a 367-amino acid polytopic membrane protein localized to the lysosomal membrane, where it functions as an H⁺-driven cystine transporter[1]. It belongs to the PQ-loop family of transporters and contains seven predicted transmembrane domains. Cystinosin is essential for preventing the toxic accumulation of cystine crystals within lysosomes and plays broader roles in [autophagy](/mechanisms/autophagy-lysosomal-pathway-parkinsons), mTORC1 signaling, and lysosomal homeostasis[2]. [@festa2018]

<div class="infobox infobox-protein"> [@kalatzis2001]

| | | [@ivanova2015]
|---|---| [@trauner2010]
| Protein Name | Cystinosin | [@bellomo2018]
| Gene | [CTNS](/genes/ctns) |
| UniProt ID | [O60931](https://www.uniprot.org/uniprot/O60931) |
| Molecular Weight | ~42 kDa (predicted), ~55 kDa (glycosylated) |
| Subcellular Localization | Lysosomal membrane |
| Function | H⁺-driven lysosomal cystine transporter |
| PDB Structures | [AlphaFold: AF-O60931](https://alphafold.ebi.ac.uk/entry/O60931) |

</div>

Structure

Domain Architecture

Cystinosin has a distinctive topology[1]:

N-terminal domain: Located in the lysosomal lumen, contains 7 N-glycosylation sites
Seven transmembrane helices (TM1-TM7): Span the lysosomal membrane to form the cystine translocation pathway
Two PQ-loop motifs: Conserved Pro-Gln sequences in TM2 and TM5 essential for transport
C-terminal tail: Cytoplasmic, contains the GYDQL lysosomal sorting motif
Intralysosomal loops: Large glycosylated loops between TMs protect against lysosomal proteases

Transport Mechanism

Cystinosin operates as a cystine/H⁺ symporter[3]:

Protons from the acidic lysosomal lumen (pH ~4.5-5.0) bind to cystinosin

Cystine (the oxidized dimer of cysteine) binds in the transport channel

Conformational change translocates both cystine and H⁺ to the cytoplasm

In the cytoplasm, cystine is reduced to two cysteine molecules by the thioredoxin system

Cysteine is used for [glutathione](/proteins/glutathione-peroxidase-protein) synthesis and protein translation

Function

Primary: Lysosomal Cystine Clearance

The canonical function of cystinosin is exporting cystine from lysosomes to prevent crystal formation[1]:

Lysosomes generate cystine through proteolytic degradation of disulfide-containing proteins
Without cystinosin, cystine accumulates to 50-100× normal levels
Cystine crystals physically damage lysosomal membranes, triggering cell death

Signaling: mTORC1 Regulation

Cystinosin interacts with components of the mTORC1 signaling pathway on the lysosomal surface[4]:

Binds to the v-ATPase/Ragulator complex that recruits mTORC1 to lysosomes
Loss of cystinosin leads to delayed mTORC1 deactivation upon nutrient starvation
Hyperactive [mTORC1](/mechanisms/mtor-signaling-neurodegeneration) suppresses [TFEB](/proteins/tfeb-protein)-mediated lysosomal biogenesis
Contributes to the defective [autophagy](/entities/autophagy) observed in cystinosis

Autophagy and Vesicular Trafficking

Cystinosin deficiency broadly impairs the endolysosomal system[2]:

Autophagic flux: Reduced autophagosome-lysosome fusion
Chaperone-mediated autophagy: Impaired LAMP2A-dependent CMA
Endosomal trafficking: Delayed endosomal maturation and cargo sorting
Lysosome biogenesis: Reduced [TFEB](/entities/tfeb) nuclear translocation impairs de novo lysosome formation

Role in Neurodegeneration

Direct Neurological Effects

Loss of cystinosin in [neurons](/entities/neurons) and glia causes[5]:

Neuronal cystine accumulation: Particularly in [hippocampal](/brain-regions/hippocampus) and [cortical](/brain-regions/cerebral-cortex) neurons
Oxidative stress: Depleted glutathione renders neurons vulnerable to [ROS](/entities/reactive-oxygen-species)
Synaptic dysfunction: Impaired vesicle recycling due to endolysosomal defects
Astrocyte pathology: Reactive astrogliosis with cystine crystal deposition
White matter disease: Progressive leukoencephalopathy and demyelination

Connections to Major Neurodegenerative Diseases

Cystinosin dysfunction highlights conserved pathogenic mechanisms[6]:

[Alzheimer's disease](/diseases/alzheimers-disease): Shared autophagy-lysosomal impairment; both show enlarged endolysosomes and impaired [Aβ](/proteins/amyloid-beta) clearance
[Parkinson's disease](/diseases/parkinsons-disease): Parallels with [GBA1](/genes/gba1)-mediated lysosomal dysfunction; [α-synuclein](/proteins/alpha-synuclein) accumulates when lysosomal function is compromised
Lysosomal storage diseases: Common pathway of lysosomal membrane damage → cathepsin release → neuroinflammation → neuronal death

Clinical Significance

Biomarker Potential

White blood cell cystine levels: Gold standard for cystinosis diagnosis and treatment monitoring
Corneal cystine crystals: Visible on slit-lamp examination, pathognomonic for cystinosis
Brain MRI: Cerebral atrophy and white matter changes correlate with neurological progression

Therapeutic Targeting

[Cysteamine](/therapeutics/cysteamine): Enters lysosomes and forms cysteine-cysteamine mixed disulfide that exits via PQLC2 transporter, bypassing the need for cystinosin
Gene therapy: AAV vectors delivering functional CTNS show promise in animal models
HSCT: Hematopoietic stem cell transplant provides cross-correction through tunneling nanotubes
[mTOR](/mechanisms/mtor-signaling-pathway) inhibitors: May correct downstream signaling defects

Protein Interactions

| Interactor | Type | Functional Consequence |
|-----------|------|----------------------|
| v-ATPase | Physical | Regulates lysosomal acidification and mTORC1 signaling |
| Ragulator complex | Physical | Modulates mTORC1 recruitment to lysosomes |
| LAMP1/LAMP2 | Co-localization | Lysosomal membrane partners |
| PQLC2 | Functional | Alternative exit route for cysteamine-cysteine mixed disulfides |
| [TFEB](/proteins/tfeb-protein) | Regulatory (indirect) | Cystinosin loss inhibits TFEB nuclear translocation |

External Links

[Cystinosin - UniProt](https://www.uniprot.org/uniprot/O60931)
[Cystinosin - AlphaFold](https://alphafold.ebi.ac.uk/entry/O60931)
[CTNS - NCBI Gene](https://www.ncbi.nlm.nih.gov/gene/1497)

References

[Town M et al., A novel gene encoding an integral membrane protein is mutated in nephropathic cystinosis (1998) (1998)](https://doi.org/10.1038/ng0698-120)

[Festa BP et al., Impaired autophagy bridges lysosomal storage disease and epithelial dysfunction in the kidney (2018) (2018)](https://doi.org/10.1038/s41467-018-03853-z)

[Kalatzis V et al., Cystinosin, the protein defective in cystinosis, is a H+-driven lysosomal cystine transporter (2001) (2001)](https://doi.org/10.1093/emboj/20.21.5940)

[Ivanova EA et al., Endo-lysosomal dysfunction in human proximal tubular epithelial cells deficient for lysosomal cystine transporter cystinosin (2015) (2015)](https://doi.org/10.1371/journal.pone.0120998)

[Trauner DA et al., Neurological impairment in nephropathic cystinosis (2010) (2010)](https://doi.org/10.1016/j.jpeds.2009.11.074)

[Bellomo F et al., Impact of atypical mitochondrial cyclic-AMP level in nephropathic cystinosis (2018) (2018)](https://doi.org/10.1007/s00018-018-2800-5)

📖 View canonical wiki page →

Related Entities

CTNSPROTEIN

▸Metadataorigin_type: v1_polymorphic_backfill

slug	proteins-ctns-protein
kg_node_id	CTNSPROTEIN
entity_type	protein
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-22605dff773c
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'proteins-ctns-protein'}
_schema_version	1

📊 Evidence Profile Foundational

Evidence Balance

+0%

Certainty

50%

Debates

0

Incoming

10

Outgoing

15

0 supporting 0 contradicting 0 neutral

View full evidence profile →

Public annotations (0)Annotate on Hypothes.is →

No public annotations yet.

📗 Cite This Artifact

Cystinosin (CTNS Protein)

Cystinosin (CTNS Protein)

Introduction

Overview

Structure

Domain Architecture

Cystinosin (CTNS Protein)

Introduction

Overview

Structure

Domain Architecture

Transport Mechanism

Function

Primary: Lysosomal Cystine Clearance

Signaling: mTORC1 Regulation

Autophagy and Vesicular Trafficking

Role in Neurodegeneration

Direct Neurological Effects

Connections to Major Neurodegenerative Diseases

Clinical Significance

Biomarker Potential

Therapeutic Targeting

Protein Interactions

See Also

External Links

References

💬 Discussion