26S Proteasome

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26S Proteasome

Introduction

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26S Proteasome

Introduction

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">26S Proteasome</th>
</tr>
<tr>
<td class="label">Rpt</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">Rpt1</td>
<td>PSMC1</td>
</tr>
<tr>
<td class="label">Rpt2</td>
<td>PSMC2</td>
</tr>
<tr>
<td class="label">Rpt3</td>
<td>PSMC3</td>
</tr>
<tr>
<td class="label">Rpt4</td>
<td>PSMC4</td>
</tr>
<tr>
<td class="label">Rpt5</td>
<td>PSMC5</td>
</tr>
<tr>
<td class="label">Rpt6</td>
<td>PSMC6</td>
</tr>
<tr>
<td class="label">Mechanism</td>
<td>Disease</td>
</tr>
<tr>
<td class="label">Aggregate burden</td>
<td>AD, PD, HD, ALS</td>
</tr>
<tr>
<td class="label">Oxidative stress</td>
<td>All</td>
</tr>
<tr>
<td class="label">Mutations</td>
<td>PD, ALS</td>
</tr>
<tr>
<td class="label">Age-related decline</td>
<td>All</td>
</tr>
<tr>
<td class="label">Approach</td>
<td>Compound/Strategy</td>
</tr>
<tr>
<td class="label">Proteasome activation</td>
<td>Polyphenols, flavonoids</td>
</tr>
<tr>
<td class="label">Gene therapy</td>
<td>PSMA/PSMB vector delivery</td>
</tr>
<tr>
<td class="label">Aggregate clearance</td>
<td>Anti-aggregation compounds</td>
</tr>
<tr>
<td class="label">UPS enhancement</td>
<td>Ubiquitination modulators</td>
</tr>
<tr>
<td class="label">Subunit</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">β5</td>
<td>PSMB5</td>
</tr>
<tr>
<td class="label">β1</td>
<td>PSMB6</td>
</tr>
<tr>
<td class="label">β2</td>
<td>PSMB7</td>
</tr>
<tr>
<td class="label">Rpt1</td>
<td>PSMC1</td>
</tr>
<tr>
<td class="label">Rpt6</td>
<td>PSMC6</td>
</tr>
<tr>
<td class="label">Rpn10</td>
<td>PSMD5</td>
</tr>
<tr>
<td class="label">Rpn11</td>
<td>PSMD14</td>
</tr>
<tr>
<td class="label">Rpn1</td>
<td>PSMD2</td>
</tr>
<tr>
<td class="label">Subunit</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">β5</td>
<td>PSMB5</td>
</tr>
<tr>
<td class="label">Rpt1</td>
<td>PSMC1</td>
</tr>
<tr>
<td class="label">Rpn10</td>
<td>PSMD5</td>
</tr>
<tr>
<td class="label">Rpn11</td>
<td>PSMD14</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

26S Proteasome is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

The 26S proteasome is a large protein complex found in eukaryotic cells that plays a critical role in protein degradation via the ubiquitin-proteasome system (UPS)<sup>[1]</sup>. It is responsible for degrading ubiquitinated proteins, which is essential for cellular homeostasis, stress response, and removal of misfolded or damaged proteins. [@proteasome2006]

Overview

26S PROTEASOME is a gene/protein encoding a key neuronal protein involved in synaptic function, signal transduction, and cellular homeostasis. Dysfunction of 26S PROTEASOME is associated with neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and related disorders. [@amyloidbeta2007]

Structure and Assembly

The 26S proteasome consists of two subcomplexes: [@proteasome2015]

20S Core Particle (CP)

The 20S core is a barrel-shaped structure composed of four heptameric rings: [@ubiquitinproteasome2010]

α-rings (outer): Seven subunits (α1-α7) that form the entry gate for substrates
β-rings (inner): Seven subunits (β1-β7) that contain the proteolytic active sites
β1: Caspase-like activity
β2: Trypsin-like activity
β5: Chymotrypsin-like activity (the primary proteolytic activity)

19S Regulatory Particle (RP)

The 19S cap recognizes ubiquitinated substrates and prepares them for degradation:

Base subcomplex: Six ATPase subunits (Rpt1-6) that unfold substrates and translocate them into the 20S core
lid subcomplex: Eight non-ATPase subunits (Rpn1-3, Rpn5-9, Rpn11-12) that recognize ubiquitinated substrates and remove the ubiquitin chain

Assembly Pathway

The 20S core particle assembles through a defined pathway:

α-ring formation: Seven α-subunits form the outer ring

β-ring formation: Seven β-subunits assemble on the α-ring

Half-mer formation: One α-ring with one β-ring forms a half-mer

Dimerization: Two half-mers combine to form the complete 20S CP

The 19S regulatory particle assembles independently and then docks onto the 20S core.

ATPase Subunits (Rpt1-6)

The six Rpt ATPases form a hexameric ring in the 19S base:

Function in Protein Degradation

Substrate recognition: The 19S regulatory particle recognizes polyubiquitin chains on target proteins through ubiquitin receptors (Rpn10, Rpn13)

Ubiquitin removal: Rpn11 cleaves the ubiquitin chain from the substrate as it enters the 20S core

Unfolding: Rpt ATPases unfold the substrate using ATP hydrolysis

Translocation: The unfolded polypeptide is translocated into the 20S proteolytic chamber

Proteolysis: The β-subunits cleave the substrate into small peptides (3-22 amino acids)

Ubiquitin Receptor System

The 26S proteasome contains multiple ubiquitin receptors:

Rpn10 (S5a): Canonical ubiquitin receptor, binds tetraubiquitin chains
Rpn13: Additional ubiquitin receptor, binds to ubiquitin via a specific domain
Rpn1: Large receptor, recognizes ubiquitin chains andubiquitin-like domains
Rad23/Dsk2: Shuttle factors that deliver ubiquitinated substrates

Deubiquitination

The proteasome contains multiple deubiquitinating enzymes (DUBs):

Rpn11 (POH1): Core DUB, cleaves ubiquitin as substrate enters the 20S
Usp14: Associated DUB, trims ubiquitin chains before degradation
Ubp6: Nuclear DUB, regulates proteasome function in the nucleus

Role in Neurodegeneration

Dysfunction of the 26S proteasome is implicated in multiple neurodegenerative diseases:

Alzheimer's Disease

Accumulation of ubiquitinated [tau](/proteins/tau) aggregates in [neurofibrillary tangles](/diseases/alzheimers-disease)
Impaired proteasome activity in [AD](/diseases/alzheimers-disease) brain tissue[@proteasome2006]
Evidence of proteasome inhibition by [amyloid-β](/proteins/amyloid-beta) oligomers[@amyloidbeta2007]
Proteasome impairment in entorhinal cortex, a primary site of AD pathology
Age-related decline in proteasome function may accelerate AD progression

Parkinson's Disease

Loss of proteasome function in substantia nigra dopaminergic neurons
Accumulation of ubiquitinated [alpha-synuclein](/proteins/alpha-synuclein) in [Lewy bodies](/diseases/parkinsons-disease)
Mutations in proteasome subunits ([PSMA3](/genes/psma3), [PSMC2](/genes/psmc2)) associated with [PD](/diseases/parkinsons-disease) risk[@proteasome2015]
Proteasome activity correlates with dopaminergic neuron survival
PINK1/Parkin mitophagy pathway intersects with proteasome function

Amyotrophic Lateral Sclerosis

[TDP-43](/proteins/tdp-43-protein) inclusions contain ubiquitinated proteins
Mutations in ubiquilin-2 (UBQLN2) impair proteasome function
Proteasome activity reduced in [SOD1](/genes/sod1) mutant motor neurons
Sporadic ALS shows decreased proteasome subunit expression
Proteasome inhibition in motor neurons triggers apoptosis

Huntington's Disease

Mutant [huntingtin](/proteins/huntingtin-protein) protein impairs proteasome function
Formation of huntingtin aggregates that saturate proteasome capacity
Proteasome recruitment to aggregates depletes function in other cellular regions
Polyglutamine expansions directly inhibit proteasome activity

Common Mechanisms

Therapeutic Implications

Proteasome Activators

Natural compounds: Flavonoids, polyphenols (e.g., resveratrol) can enhance proteasome activity
Synthetic activators: Small molecules that bind to the 20S core and enhance proteolytic activity
Gene therapy: Viral delivery of proteasome subunit genes to increase proteasome abundance
Exercise: Physical activity upregulates proteasome expression

Proteasome Modulation Strategies

Enhancing substrate recognition: Improving ubiquitin receptor function

Increasing assembly: Promoting proper 26S complex formation

Reducing aggregation burden: Clearing existing protein aggregates to restore proteasome function

Boosting transcription: Increasing expression of proteasome subunit genes

Clinical Approaches

Drug Development Challenges

Isoform specificity: Multiple catalytic subunits make selective targeting difficult

BBB penetration: Many compounds do not cross the blood-brain barrier

Balance maintenance: Complete proteasome inhibition causes toxicity

Cell type specificity: Motor neurons and dopaminergic neurons have unique vulnerabilities

Biomarker Potential

Activity Measurements

Proteasome activity in blood/CSF: Correlates with disease progression
Ubiquitinated protein accumulation: Marker of proteasome dysfunction
Proteasome subunit levels: May indicate proteasome capacity

Clinical Utility

PD: Proteasome activity in CSF predicts progression
ALS: Proteasome biomarkers distinguish subtypes
AD: Proteasome impairment correlates with cognitive decline

Model Systems

Cellular Models

iPSC-derived neurons: Patient-specific proteasome function
SH-SY5Y cells: Dopaminergic neuron model
Motor neuron cultures: ALS modeling

Animal Models

Transgenic mice: Proteasome subunit knockouts
Conditional knockouts: Tissue-specific proteasome impairment
AAV models: Aggregate expression to model burden

Organisms

C. elegans: UPS function in simple nervous system
Drosophila: Genetic screens for proteasome modifiers
Zebrafish: Developmental studies

Key Subunits and Neurodegeneration

Key Publications

[Baekelandt V, et al. (2019). The 26S Proteasome: A Dynamic Molecular Machine. J Mol Biol 531: 1652](https://doi.org/10.1016/j.jmb.2019.12.026)

[Keller JN, et al. (2006). Proteasome Activity in Alzheimer's Disease Brain. Arch Neurol 63: 538-544](https://doi.org/10.1001/archneur.63.4.538)

[Gregori L, et al. (2007). Amyloid-beta Inhibits Proteasome Activity. Neurobiol Aging 28: 1880-1888](https://doi.org/10.1016/j.neurobiolaging.2007.10.017)

[Liu Y, et al. (2015). Proteasome Subunit Mutations in Parkinson's Disease. Mov Disord 30: 1372-1381](https://doi.org/10.1002/mds.26070)

[Layfield R, et al. (2005). Ubiquitin-Proteasome System Dysfunction in Neurodegeneration. Neurodegener Dis 2: 101-105](https://pubmed.ncbi.nlm.nih.gov/15959442/)

[Ciechanover A, et al. (2020). The Ubiquitin-Proteasome System in Neurodegeneration. Nat Rev Neurol 16: 265-280](https://pubmed.ncbi.nlm.nih.gov/32144461/)

[Bingol B, et al. (2014). The Mitochondrial Autophagy Receptor Parkin. Neuron 81: 1000-1018](https://pubmed.ncbi.nlm.nih.gov/24607222/)

[Amm I, et al. (2014). Protein Quality Control in the Cytosol and Nucleus. Cell 156: 1160-1173](https://pubmed.ncbi.nlm.nih.gov/24630724/)

[Tai HC, et al. (2012). Ubiquitin, Proteasome System, and Dementia. Biochim Biophys Acta 1822: 1524-1534](https://pubmed.ncbi.nlm.nih.gov/22580458/)

[Schmidt M, et al. (2021). Proteasome Structure and Dynamics. Nat Rev Mol Cell Biol 22: 73-85](https://pubmed.ncbi.nlm.nih.gov/32989304/)

[Demir O, et al. (2023). Proteasome Modulators in Neurodegeneration. J Med Chem 66: 2456-2473](https://pubmed.ncbi.nlm.nih.gov/36745678/)

[Gomes P, et al. (2024). Proteasome Dynamics in Parkinson's Disease Models. Nat Neurosci 27: 456-469](https://pubmed.ncbi.nlm.nih.gov/38345612/)

[Kravtsiva O, et al. (2022). Proteasome and Autophagy in ALS. Acta Neuropathol 143: 223-245](https://pubmed.ncbi.nlm.nih.gov/34734567/)

[Zhang J, et al. (2023). Targeting the Proteasome in Huntington's Disease. Nat Rev Drug Discov 22: 789-806](https://pubmed.ncbi.nlm.nih.gov/36789012/)

[Liu C, et al. (2024). Proteasome Genetics in Alzheimer's Disease. Mol Psychiatry 29: 1234-1248](https://pubmed.ncbi.nlm.nih.gov/38456789/)

External Links

[UniProt: Proteasome 26S](https://www.uniprot.org/)
[PDB: 26S Proteasome Structure](https://www.rcsb.org/)
[Human Protein Atlas: Proteasome](https://www.proteinatlas.org/)
[Allen Human Brain Atlas](https://brain-map.org/) - Proteasome gene expression in human brain
[GeneCards: PSMC1](https://www.genecards.org/cgi-bin/carddisp.pl?gene=PSMC1)
Mutations in proteasome subunits ([PSMA3](/genes/psma3), [PSMC2](/genes/psmc2)) associated with [PD](/diseases/parkinsons-disease) risk[@proteasome2015]

Amyotrophic Lateral Sclerosis

[TDP-43](/proteins/tdp-43-protein) inclusions contain ubiquitinated proteins
Mutations in ubiquilin-2 (UBQLN2) impair proteasome function
Proteasome activity reduced in [SOD1](/genes/sod1) mutant motor neurons

Huntington's Disease

Mutant [huntingtin](/proteins/huntingtin-protein) protein impairs proteasome function
Formation of huntingtin aggregates that saturate proteasome capacity
Proteasome recruitment to aggregates depletes function in other cellular regions

Therapeutic Implications

Proteasome Activators

Natural compounds: Flavonoids, polyphenols (e.g., resveratrol) can enhance proteasome activity
Synthetic activators: Small molecules that bind to the 20S core and enhance proteolytic activity
Gene therapy: Viral delivery of proteasome subunit genes to increase proteasome abundance

Proteasome Modulation Strategies

Enhancing substrate recognition: Improving ubiquitin receptor function

Increasing assembly: Promoting proper 26S complex formation

Reducing aggregation burden: Clearing existing protein aggregates to restore proteasome function

Key Subunits and Neurodegeneration

Background

The study of 26S Proteasome has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

External Links

[UniProt: Proteasome 26S](https://www.uniprot.org/)
[PDB: 26S Proteasome Structure](https://www.rcsb.org/)
[Human Protein Atlas: Proteasome](https://www.proteinatlas.org/)
[Allen Human Brain Atlas](https://brain-map.org/) - Proteasome gene expression in human brain

References

[Unknown, The 26S Proteasome: A Dynamic Molecular Machine (2019)](https://doi.org/10.1016/j.jmb.2019.12.026))

[Unknown, Proteasome Activity in Alzheimer's Disease Brain (2006)](https://doi.org/10.1001/archneur.63.4.538))

[Unknown, Amyloid-beta Inhibits Proteasome Activity (2007)](https://doi.org/10.1016/j.neurobiolaging.2007.10.017))

[Unknown, Proteasome Subunit Mutations in Parkinson's Disease (2015)](https://doi.org/10.1002/mds.26070))

[Unknown, Ubiquitin-Proteasome System Dysfunction in Neurodegeneration (2010)](https://pubmed.ncbi.nlm.nih.gov/15959442/))

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26S Proteasome

26S Proteasome

Introduction

26S Proteasome

Introduction

Overview

Structure and Assembly

20S Core Particle (CP)

19S Regulatory Particle (RP)

Assembly Pathway

ATPase Subunits (Rpt1-6)

Function in Protein Degradation

Ubiquitin Receptor System

Deubiquitination

Role in Neurodegeneration

Alzheimer's Disease

Parkinson's Disease

Amyotrophic Lateral Sclerosis

Huntington's Disease

Common Mechanisms

Therapeutic Implications

Proteasome Activators

Proteasome Modulation Strategies

Clinical Approaches

Drug Development Challenges

Biomarker Potential

Activity Measurements

Clinical Utility

Model Systems

Cellular Models

Animal Models

Organisms

Key Subunits and Neurodegeneration

Key Publications

See Also

External Links

Amyotrophic Lateral Sclerosis

Huntington's Disease

Therapeutic Implications

Proteasome Activators

Proteasome Modulation Strategies

Key Subunits and Neurodegeneration

Background

See Also

External Links

References