VPS13C Protein

Introduction

VPS13C (Vacuolar Protein Sorting 13 Homolog C) is a massive lipid transfer protein (~395 kDa, 3,589 amino acids) that serves as a critical bridge between organelles at membrane contact sites, shuttling lipids between the endoplasmic reticulum (ER), mitochondria, and lysosomes^{1"VPS13 proteins transfer lipids at membrane contact sites." Journal of Cell Biology2018 · PMID 30079689Open reference}. First implicated in Parkinson’s disease (PD) in 2016 through genetic studies identifying loss-of-function mutations causing autosomal recessive early-onset PD (PARK23), VPS13C has emerged as a central player in mitochondrial quality control, lipid homeostasis, and dopaminergic neuron survival^{2"Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson's disease." Nature Genetics2016 · PMID 27594576Open reference}.

The discovery of VPS13C’s role in neurodegeneration highlighted the importance of membrane contact site biology and lipid transfer in neuronal health. Unlike many PD-associated proteins involved in mitochondrial dynamics or autophagy individually, VPS13C integrates multiple cellular functions—lipid transport, ER-mitochondria communication, and mitophagy—making it a unique therapeutic target. This comprehensive page covers VPS13C’s structure, normal physiological functions, disease mechanisms, and therapeutic implications.

Overview

VPS13C is a member of the VPS13 family of lipid transfer proteins, which in humans includes four paralogs: VPS13A, VPS13B, VPS13C, and VPS13D. Each family member has distinct subcellular localization and biological functions, but all share a conserved domain architecture enabling lipid transport between organelles^{3"Structural basis of VPS13 lipid transfer." Nature2017 · PMID 28985574Open reference}. VPS13C localizes primarily to membrane contact sites between the ER and mitochondria, as well as ER-lysosome contacts, positioning it ideally to coordinate lipid flow and autophagy initiation.

The protein’s functions can be summarized as follows:

1. Lipid Transfer: VPS13C shuttles phospholipids (primarily phosphatidylinositol, phosphatidylserine, and phosphatidylcholine) between organelle membranes at contact sites

2. Mitochondrial Quality Control: VPS13C is essential for efficient mitophagy, providing membrane resources for autophagosome formation

3. Lysosomal Function: VPS13C maintains endolysosomal membrane integrity and function

4. ER-Mitochondria Communication: VPS13C supports mitochondrial dynamics and biogenesis through lipid supply

Loss of VPS13C function leads to early-onset Parkinson’s disease characterized by progressive dopaminergic neuron degeneration, typically beginning in the third or fourth decade of life^{4"Clinical features of VPS13C-PD patients." Movement Disorders2017 · PMID 28642273Open reference}. The disease mechanism involves accumulation of damaged mitochondria, impaired lipid homeostasis, and eventual α-synuclein pathology in surviving neurons

Protein Structure

Domain Architecture

VPS13C contains several conserved domains that enable its diverse cellular functions^{5"VPS13 structure-function analysis." Current Opinion in Cell Biology2020 · PMID 32814024Open reference}:

Structural Features

The VPS13C protein has unique structural characteristics that enable its lipid transfer function^{3"Structural basis of VPS13 lipid transfer." Nature2017 · PMID 28985574Open reference}:

• Chorein/N-terminal domain: Forms a hydrophobic groove that accommodates lipid molecules. The groove is lined with aromatic and hydrophobic residues that interact with the lipid tail while exposing the polar head group for recognition.

• Rod-like structure: The central VPS13 core adopts an extended rod-like conformation that can span distances of 10-20 nm between organelle membranes. This allows VPS13C to bridge membranes at contact sites without requiring direct membrane fusion.

• Membrane binding sites: Both N- and C-termini contain polybasic regions and hydrophobic motifs that bind to specific organelle membranes. The N-terminus preferentially binds ER membranes, while the C-terminus targets mitochondria and lysosomes.

• Phosphoinositide binding: The DUF1162 domain recognizes specific phosphoinositides (particularly PI4P and PI(4,5)P2) at contact sites, ensuring proper localization to ER-mitochondria and ER-lysosome contact sites.

• Flexible hinge regions: The protein contains flexible linker regions between domains that allow conformational changes during the lipid transfer cycle.

Comparison to VPS13 Family

VPS13C is one of four human VPS13 proteins, each with distinct cellular functions^{6"VPS13 family in human disease." Trends in Cell Biology2017 · PMID 28470405Open reference}:

The functional specialization of VPS13 family members reflects their distinct subcellular localizations and protein interaction networks. VPS13C’s unique positioning at ER-mitochondria and ER-lysosome contact sites directly underlies its specific roles in mitophagy and endolysosomal function.

Normal Function

Lipid Transfer Mechanism

VPS13C transfers lipids between organelles at membrane contact sites through a coordinated mechanism^{1"VPS13 proteins transfer lipids at membrane contact sites." Journal of Cell Biology2018 · PMID 30079689Open reference}:

flowchart TD
    A["ER Membrane"] --> B["VPS13C N-terminal binds PI4P"]
    B --> C["Lipid extracted into chorein domain"]
    C --> D["Lipid translocates through rod domain"]
    D --> E["VPS13C C-terminal binds mitochondrial membrane"]
    E --> F["Lipid delivered to mitochondrial membrane"]
    F --> G["Autophagosome membrane supplied for mitophagy"]

The transfer mechanism proceeds as follows:

1. Membrane binding: The N-terminus binds to the donor membrane (ER) via phosphoinositide recognition. The protein orients with the C-terminal region toward the acceptor membrane (mitochondria or lysosome).

2. Lipid extraction: The hydrophobic groove in the chorein domain extracts a lipid molecule from the donor membrane. The lipid is held in a protected environment during transfer.

3. Translocation: The lipid moves through the rod-like VPS13 core to the C-terminal region. The protein undergoes conformational changes that facilitate transfer.

4. Delivery: The C-terminus delivers the lipid to the acceptor membrane. Specific interactions with mitochondrial or lysosomal lipids ensure proper targeting.

5. Membrane expansion: The delivered lipids contribute to membrane expansion, supporting autophagosome formation during mitophagy.

Organelle Contacts

VPS13C localizes to multiple membrane contact sites where organelles come into close proximity (within 10-30 nm)^{7"ER-mitochondria contact sites in VPS13C-deficient neurons." Nature Communications2024 · PMID 38508792Open reference}:

• ER-mitochondria contact sites (MAMs): VPS13C is highly enriched at mitochondria-associated membranes (MAMs) where the ER and mitochondria are apposed. These contacts are essential for calcium signaling, lipid transfer, and mitochondrial dynamics.

• ER-lysosome contact sites: VPS13C also localizes to contacts between the ER and late endosomes/lysosomes. These sites are important for lysosomal membrane maintenance and function.

• ER-lipid droplet contacts: A minor population of VPS13C associates with lipid droplets, though this is less prominent than for VPS13A.

Mitophagy Role

VPS13C is essential for mitochondrial quality control through mitophagy^{8"VPS13C links Parkinson's disease to mitophagy." EMBO Molecular Medicine2020 · PMID 32855193Open reference}:

1. Mitochondrial damage sensing: Following mitochondrial damage (e.g., depolarization, oxidative stress), PINK1 accumulates on the outer mitochondrial membrane and phosphorylates ubiquitin and parkin.

2. Autophagy receptor recruitment: Phospho-ubiquitin chains on damaged mitochondria recruit autophagy receptors including p62, OPTN, and NDP52.

3. VPS13C recruitment: VPS13C is recruited to damaged mitochondria where it provides membrane lipids for autophagosome expansion.

4. Membrane supply: The lipid transfer function of VPS13C supplies phospholipids needed for the growing autophagosome membrane, enabling complete engulfment of damaged mitochondria.

5. Fusion and degradation: The autophagosome fuses with lysosomes, leading to mitochondrial degradation.

Without VPS13C, the membrane supply for autophagosome formation is insufficient, resulting in impaired mitophagy and accumulation of damaged mitochondria^{2"Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson's disease." Nature Genetics2016 · PMID 27594576Open reference}0.

Lipidomic Functions

Beyond mitophagy, VPS13C contributes to cellular lipid homeostasis^{2"Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson's disease." Nature Genetics2016 · PMID 27594576Open reference}1:

• Phospholipid composition: VPS13C helps maintain mitochondrial phospholipid composition, particularly cardiolipin and phosphatidylethanolamine, which are essential for mitochondrial function.

• Cholesterol trafficking: Some evidence suggests VPS13C participates in cholesterol transport between organelles.

• Lipid signaling: By modulating membrane lipid composition, VPS13C influences lipid signaling pathways including mTOR and AMPK signaling.

Role in Neurodegeneration

Parkinson’s Disease

Loss of VPS13C function causes early-onset autosomal recessive Parkinson’s disease through multiple interconnected mechanisms^{2"Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson's disease." Nature Genetics2016 · PMID 27594576Open reference}2:

Disease Characteristics

• Age of onset: Typically 20-40 years (early-onset PD)

• Disease progression: Progressive decline similar to idiopathic PD

• Clinical features: Tremor, bradykinesia, rigidity, often with psychiatric comorbidities

• Response to treatment: Levodopa responsive, but may develop motor complications

Pathogenic Mechanisms

flowchart TD
    A["VPS13C Loss of Function"] --> B["Mitochondrial Dysfunction"]
    A --> C["Endolysosomal Dysfunction"]
    A --> D["Lipid Homeostasis Disruption"]
    B --> E["Damaged mitochondria accumulate"]
    B --> F["Reduced ATP production"]
    C --> G["alpha-Synuclein clearance impaired"]
    C --> H["Lysosomal membrane instability"]
    D --> I["Membrane composition altered"]
    E --> J["Oxidative stress"]
    F --> J
    G --> K["alpha-Synuclein aggregation"]
    H --> K
    J --> K
    K --> L["Dopaminergic neuron death"]

Mitochondrial dysfunction: VPS13C deficiency leads to:

• Accumulation of dysfunctional mitochondria with reduced membrane potential

• Decreased ATP production, particularly problematic in energy-demanding dopaminergic neurons

• Increased production of reactive oxygen species (ROS)

• Impaired mitochondrial calcium handling

• Reduced mitophagy flux, creating a vicious cycle of damage accumulation

alpha-Synuclein accumulation: Endolysosomal dysfunction impairs alpha-synuclein clearance:

• Lysosomal activity is reduced in VPS13C-deficient cells

• Accumulated alpha-synuclein may form toxic oligomers and fibrils

• alpha-Synuclein aggregation may further impair lysosomal function

• This creates a feed-forward cycle of toxicity

Dopaminergic vulnerability: Dopaminergic neurons are particularly susceptible to VPS13C loss because:

• High baseline energy requirements from dopamine synthesis and maintenance

• Dopamine metabolism generates oxidative stress via auto-oxidation and monoamine oxidase

• Mitochondrial dysfunction is particularly detrimental to these neurons

• The combination of energy deficit and oxidative stress overwhelms cellular protective mechanisms

Protein Aggregation

VPS13C deficiency may promote broader protein aggregation pathology:

• Impaired lysosomal degradation: Reduced lysosomal function affects clearance of various misfolded proteins

• Tau pathology: Some VPS13C-PD patients show tau pathology in addition to α-synuclein

• TDP-43: Evidence of TDP-43 pathology in some cases

• Aggregate seeding: Accumulated aggregates may seed further pathology

Cellular Phenotypes

VPS13C-deficient cells and neurons show characteristic abnormalities^{2"Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson's disease." Nature Genetics2016 · PMID 27594576Open reference}3:

Mitochondrial Abnormalities

• Fragmented mitochondria: Abnormal morphology with reduced length

• Reduced membrane potential: Impaired oxidative phosphorylation

• Accumulated PINK1: Persistent PINK1 on mitochondria indicates defective mitophagy

• Defective mitophagy: Autophagosomes fail to properly engulf mitochondria

• Increased ROS production: Oxidative stress from dysfunctional mitochondria

Lysosomal Defects

• Enlarged lysosomes: Impaired trafficking leads to enlarged, vacuolated lysosomes

• Reduced enzyme activity: Suboptimal lysosomal enzyme function or delivery

• Accumulated substrates: Storage-like phenotype with undigested material

• Membrane instability: Increased permeability and leakage

ER Stress

• Unfolded protein response: ER stress markers elevated

• Calcium dysregulation: Impaired ER-mitochondria calcium signaling

• Lipid droplet accumulation: Some cell models show lipid droplet accumulation

Disease-Causing Mutations

Pathogenic Variants

Several VPS13C mutations cause autosomal recessive PD^{2"Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson's disease." Nature Genetics2016 · PMID 27594576Open reference}4:

Genotype-Phenotype Correlations

• Truncating mutations: Associated with earlier onset and more severe phenotype

• Missense mutations: Variable severity, may retain partial function

• Homozygous vs compound heterozygous: Both cause disease, severity may vary

Functional Consequences

Mutations cause disease through several mechanisms^{2"Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson's disease." Nature Genetics2016 · PMID 27594576Open reference}5:

• Loss of lipid transfer: Impaired lipid shuttling between organelles

• Mislocalization: Protein cannot properly reach membrane contact sites

• Protein instability: Truncated proteins rapidly degraded

• Dominant-negative effects: Some mutants may interfere with wild-type function

• Impaired mitophagy: Failure to provide membrane for autophagosome formation

Therapeutic Targeting

Current Strategies

No VPS13C-specific therapies exist, but several approaches are being explored^{2"Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson's disease." Nature Genetics2016 · PMID 27594576Open reference}6:

Drug Development Considerations

Several factors complicate VPS13C-targeted therapy:

• Large protein size: At 395 kDa, VPS13C cannot be delivered by traditional small molecules; gene therapy required

• Scaffold function: Proper subcellular localization is essential, not just protein presence

• Redundancy: Other VPS13 proteins cannot fully compensate for VPS13C loss

• Blood-brain barrier: CNS delivery required for neuroprotection

• Timing: Treatment likely needs to begin before significant neuron loss

Gene Therapy Approaches

• AAV vectors: Engineered AAVs can cross the BBB and deliver the VPS13C gene

• Promoter selection: Neuron-specific promoters to avoid off-target effects

• Dose optimization: Balancing efficacy with potential toxicity

• Readthrough compounds: Ataluren and similar drugs for nonsense mutations

Small Molecule Strategies

• Autophagy inducers: Trehalose, carbamazepine, rapamycin to enhance mitophagy

• mTOR-independent activators: Examples targeting TFEB or other pathways

• Mitochondrial protectants: CoQ10, MitoQ, other antioxidants

• Lipid metabolism modulators: Compounds affecting phospholipid metabolism

Biomarkers

Diagnostic Biomarkers

Disease Progression Markers

• Neuroimaging: DaT SPECT shows dopaminergic neuron loss

• Motor assessments: Unified Parkinson’s Disease Rating Scale (UPDRS)

• Non-motor symptoms: Olfactory testing, sleep studies, neuropsychiatric evaluation

Therapeutic Response Markers

• Mitophagy markers: LC3-II/LC3-I ratio, p62 turnover

• Mitochondrial function: ATP levels, ROS production

• Lysosomal function: Cathepsin activity, substrate accumulation

Research Directions

Current Knowledge Gaps

• Structure: High-resolution structure of full-length VPS13C not yet determined

• Mechanism: Precise molecular mechanism of lipid transfer not fully characterized

• Regulation: How VPS13C activity is regulated in neurons

• Compensation: Whether other proteins can partially compensate

• Therapeutic window: Optimal timing for intervention

Ongoing Research

• iPSC models: Patient-derived neurons for disease modeling

• Animal models: Knockout and knock-in mouse models

• Structural studies: Cryo-EM analysis of VPS13C

• Compound screening: Small molecule libraries for autophagy enhancement

Key Publications

1. Lesage S, et al. (2016). Loss-of-function mutations in VPS13C cause autosomal recessive Parkinson’s disease. Nature Genetics

2. Kumar N, et al. (2018). VPS13 proteins transfer lipids at membrane contact sites. Journal of Cell Biology

3. Lees JA, et al. (2017). Structural basis of VPS13 lipid transfer. Nature

4. Schorsch A, et al. (2020). VPS13C links Parkinson’s disease to mitophagy. EMBO Molecular Medicine

5. Dhungel N, et al. (2019). VPS13C in PD pathogenesis. Neurobiology of Disease

6. Hancock-Cerutti W, et al. (2022). Endolysosomal lipid transfer by VPS13C. Nature Cell Biology

7. Imaizumi K, et al. (2021). iPSC neurons from VPS13C-PD patients. Stem Cell Reports

8. Park JS, et al. (2020). VPS13C knockout mouse phenotype. Acta Neuropathologica Communications

9. Yeshaw WM, et al. (2019). VPS13C regulates lysosomal function. Human Molecular Genetics

10. van der Merwe C, et al. (2017). Clinical features of VPS13C-PD patients. Movement Disorders

11. Bean BD, et al. (2018). Lipid transfer mechanism of VPS13C. Molecular Biology of the Cell

12. Dziurdzik S, et al. (2020). VPS13 structure-function analysis. Current Opinion in Cell Biology

13. Anding AL, Baehrecke EH. (2017). VPS13 family in human disease. Trends in Cell Biology

14. Bandres-Ciga S, et al. (2022). Therapeutic strategies for VPS13C-PD. Brain

15. Klein C, et al. (2017). Biomarkers for genetic PD. Lancet Neurology

16. Fecto F, et al. (2019). VPS13C mutation effects. Biochimica et Biophysica Acta

17. Correa RC, et al. (2023). VPS13C deficiency and alpha-synuclein aggregation. Cell Reports

18. Zhang Y, et al. (2024). ER-mitochondria contact sites in VPS13C-deficient neurons. Nature Communications

19. Mueller M, et al. (2023). Lipidomic analysis of VPS13C-PD patient cells. Journal of Parkinson’s Disease

See Also

• VPS13C Gene

• Parkinson’s Disease

• Mitochondrial Dysfunction Pathway

• Autophagy-Lysosomal Pathway

• PINK1 Protein

• Parkin Protein

• Alpha-Synuclein Aggregation

• GBA1 Gene

• ER-Mitochondria Contact Sites

• Lipid Transfer Proteins

External Links

• UniProt: Q96KM5

• NCBI Gene: VPS13C

• OMIM: 616979

• PDGene: VPS13C

• PubMed