The VPS33B gene encodes VPS33B (Vacuolar Protein Sorting 33 homolog B), a critical component of the HOPS (Homotypic fusion and Protein Sorting) tethering complex that facilitates lysosomal fusion and autophagy. VPS33B belongs to the Sec1/Munc18 (SM) family of proteins that regulate vesicle trafficking and is essential for neuronal function, synaptic plasticity, and the clearance of protein aggregates that accumulate in neurodegenerative diseases [1].
| VPS33B Gene | |
|---|---|
| Gene Symbol | VPS33B |
| Full Name | Vacuolar Protein Sorting 33 Homolog B |
| Chromosomal Location | 15q26.1 |
| NCBI Gene ID | [124976](https://www.ncbi.nlm.nih.gov/gene/124976) |
| OMIM | 613299 |
| Ensembl ID | ENSG00000011201 |
| UniProt ID | [Q9H0M0](https://www.uniprot.org/uniprot/Q9H0M0) |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), ARC Syndrome |
VPS33B functions as part of the evolutionarily conserved HOPS tethering complex, a hexameric assembly that bridges vesicle fusion machinery to facilitate lysosomal and autophagosomal fusion events [2]:
| Subunit | Gene | Molecular Weight | Function |
|---|---|---|---|
| VPS11 | VPS11 | 110 kDa | Core subunit, binds to membranes via FYVE domain |
| VPS16 | VPS16 | 90 kDa | Scaffold, binds VPS33 proteins |
| VPS18 | VPS18 | 110 kDa | Core subunit, forms heterotetramer |
| VPS33A | VPS33A | 62 kDa | SM protein isoform, regulates SNARE |
| VPS33B | VPS33B | 60 kDa | Neuronal SM protein, regulates SNARE complex |
| VPS39 | VPS39 | 100 kDa | Tethering protein, vacuolar H+-ATPase interaction |
| VPS41 | VPS41 | 95 kDa | Tethering protein, involved in membrane docking |
The two SM proteins, VPS33A and VPS33B, arise from alternative splicing and have tissue-specific expression patterns. VPS33B is predominantly expressed in the brain and neurons, while VPS33A is more broadly expressed in other tissues.
VPS33B participates in several critical cellular processes:
Autophagosome-Lysosome Fusion: VPS33B is essential for the final step of autophagy where autophagosomes fuse with lysosomes to form autolysosomes, enabling degradation of aggregated proteins [3]
Lysosomal Enzyme Delivery: The HOPS complex facilitates trafficking of lysosomal hydrolases from the trans-Golgi network to lysosomes
Synaptic Vesicle Recycling: In neurons, VPS33B regulates synaptic vesicle reformation and trafficking at presynaptic terminals
Endosomal Maturation: VPS33B contributes to endosomal-lysosomal trafficking pathways that clear cellular debris
VPS33B interacts with key proteins involved in neurodegeneration:
VPS33B dysfunction may contribute to Alzheimer's disease pathogenesis through impaired lysosomal function [4:1]:
Amyloid Clearance: Lysosomal degradation of amyloid-beta requires functional autophagosome-lysosome fusion, which depends on VPS33B
Tau Clearance: Autophagy-lysosome pathways are critical for clearing hyperphosphorylated tau aggregates
Cellular Stress Response: Impaired lysosomal function leads to accumulation of damaged organelles and protein aggregates, triggering cellular stress
Microglial Function: VPS33B in microglia affects clearance of amyloid plaques and cellular debris
In Parkinson's disease, VPS33B plays important roles in the clearance of alpha-synuclein aggregates [5]:
Alpha-Synuclein Degradation: Autophagy-lysosome pathways are major routes for clearing toxic alpha-synuclein oligomers and fibrils
Lysosomal Function: PD-linked mutations in GBA1 (glucocerebrosidase) impair lysosomal function, and VPS33B-mediated pathways may compensate
Mitochondrial Quality Control: Lysosomal dysfunction affects mitophagy, the process for clearing damaged mitochondria
Dopaminergic Neuron Vulnerability: The substantia nigra dopaminergic neurons are particularly dependent on efficient lysosomal clearance
VPS33B dysfunction may also contribute to ALS through:
VPS33B exhibits specific expression patterns in the central nervous system:
In neurons, VPS33B localizes to:
Biallelic VPS33B mutations cause Arthrogryposis, Renal dysfunction, Cholestasis (ARC) syndrome [1:1]:
Carriers of VPS33B variants may have increased risk for:
VPS33B expression levels in cerebrospinal fluid (CSF) or blood may serve as:
Cullinane AR, et al. The spectrum of VPS33B-related disorders. Human Molecular Genetics. 2015. ↩︎ ↩︎
Liu J, et al. HOPS complex in neuronal function. Progress in Neurobiology. 2020. ↩︎
Kim S, et al. VPS33B in protein aggregation clearance. Autophagy. 2022. ↩︎
Yang M, et al. Lysosomal dysfunction in Alzheimer's disease. Acta Neuropathologica Communications. 2019. ↩︎ ↩︎
Chen X, et al. Autophagy-lysosome pathway in Parkinson's disease. Nature Reviews Neurology. 2021. ↩︎