vps13c-protein
Overview
VPS13C (vacuolar protein sorting-associated protein 13C) is a large cytoplasmic protein encoded by the VPS13C gene located on chromosome 16q24.2. This protein belongs to the VPS13 family, a conserved group of lipid transport proteins found across eukaryotes. VPS13C is approximately 350 kDa in molecular weight and functions as a lipid transporter at membrane contact sites, facilitating the transfer of lipids between cellular compartments. The protein has gained significant attention in neurodegeneration research due to its association with neurological disorders, particularly through loss-of-function mutations that impair neuronal integrity and survival.
Function/Biology
VPS13C operates as a lipid transporter protein that mediates non-vesicular lipid transport between organellar membranes. The protein contains multiple functional domains, including a characteristic VPS13 domain that enables its role in lipid binding and transfer. VPS13C localizes to membrane contact sites, specialized regions where the endoplasmic reticulum (ER) makes close apposition with other organelles such as mitochondria and the trans-Golgi network. At these sites, VPS13C facilitates the transfer of glycerophospholipids, particularly phosphatidylinositol (PI) and phosphatidylserine (PS), between membrane compartments.
...vps13c-protein
Overview
VPS13C (vacuolar protein sorting-associated protein 13C) is a large cytoplasmic protein encoded by the VPS13C gene located on chromosome 16q24.2. This protein belongs to the VPS13 family, a conserved group of lipid transport proteins found across eukaryotes. VPS13C is approximately 350 kDa in molecular weight and functions as a lipid transporter at membrane contact sites, facilitating the transfer of lipids between cellular compartments. The protein has gained significant attention in neurodegeneration research due to its association with neurological disorders, particularly through loss-of-function mutations that impair neuronal integrity and survival.
Function/Biology
VPS13C operates as a lipid transporter protein that mediates non-vesicular lipid transport between organellar membranes. The protein contains multiple functional domains, including a characteristic VPS13 domain that enables its role in lipid binding and transfer. VPS13C localizes to membrane contact sites, specialized regions where the endoplasmic reticulum (ER) makes close apposition with other organelles such as mitochondria and the trans-Golgi network. At these sites, VPS13C facilitates the transfer of glycerophospholipids, particularly phosphatidylinositol (PI) and phosphatidylserine (PS), between membrane compartments.
The protein interacts with multiple binding partners including members of the TETHER family of proteins and other lipid transport machinery. These interactions are essential for VPS13C to maintain its subcellular localization and execute its lipid transfer function. Additionally, VPS13C participates in membrane dynamics and organellar organization, contributing to the maintenance of proper subcellular architecture necessary for normal cellular physiology.
Role in Neurodegeneration
Loss-of-function mutations in VPS13C cause autosomal recessive cerebellar ataxia with spasticity and/or vertical supranuclear palsy (ARCASP). Affected individuals typically present with progressive cerebellar ataxia, lower limb spasticity, and oculomotor dysfunction. The neurological manifestations suggest particular vulnerability of cerebellar neurons and brainstem structures, though the pathophysiological mechanism remains incompletely understood.
The selective neuronal vulnerability associated with VPS13C deficiency may reflect the heightened dependence of neurons on efficient lipid homeostasis and mitochondrial function. Neurons maintain extensive intracellular membrane networks required for synaptic transmission and axonal integrity, making them particularly susceptible to defects in lipid transport. VPS13C dysfunction compromises the supply of essential phospholipids to mitochondria, potentially impairing oxidative phosphorylation and energy production critical for neuronal survival.
Molecular Mechanisms
At the molecular level, VPS13C dysfunction disrupts lipid homeostasis at membrane contact sites. The protein's lipid transport activity depends on a functional Vps13 lipid-binding domain that can accommodate and shuttle lipids across the aqueous space between apposed membranes. Loss-of-function mutations impair this transport capacity, leading to accumulation of lipids at the ER and deficient lipid delivery to target organelles.
Impaired phospholipid transfer to mitochondria compromises the composition of the mitochondrial inner membrane, affecting the assembly and function of the electron transport chain. This results in reduced ATP production and increased generation of reactive oxygen species (ROS). Simultaneously, disrupted phosphatidylinositol (PI) signaling cascades affect various cellular processes including autophagy, vesicular trafficking, and cytoskeletal dynamics.
VPS13C deficiency also appears to impair autophagy-mediated clearance of dysfunctional mitochondria (mitophagy), leading to accumulation of damaged organelles. Neurons particularly depend on efficient mitophagy for maintenance of mitochondrial quality control; defects in this process contribute to neuronal degeneration and death.
Clinical/Research Significance
VPS13C mutations represent an important genetic cause of ataxia and related movement disorders. Identifying VPS13C as a disease gene has expanded understanding of how lipid transport dysfunction can drive neurodegeneration. Research into VPS13C function has broader implications for understanding other neurodegenerative conditions involving mitochondrial dysfunction and cellular stress.
Current research focuses on characterizing the structural determinants of VPS13C's lipid-binding capacity, identifying tissue-specific cofactors affecting protein function, and developing therapeutic approaches to restore or compensate for impaired lipid transport in affected individuals.
- VPS13 family proteins (VPS13A, VPS13B, VPS13D): paralogous proteins with partially overlapping functions
- Cerebellar ataxia: clinical manifestation of VPS13C dysfunction
- Membrane contact sites: subcellular structures where VPS13C functions
- Phospholipid transport: biological process mediated by VPS13C
- Mitochondrial dysfunction: consequence of VPS13C deficiency
- Autophagy and mitophagy: cellular processes affected by VPS13C loss