Ubiquitin

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Ubiquitin

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Ubiquitin

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Ubiquitin</th>
</tr>
<tr>
<td class="label">Linkage</td>
<td>Function</td>
</tr>
<tr>
<td class="label">K48</td>
<td>Proteasomal degradation</td>
</tr>
<tr>
<td class="label">K63</td>
<td>Endocytosis, signaling, [autophagy](/entities/autophagy)</td>
</tr>
<tr>
<td class="label">K11</td>
<td>Cell cycle regulation</td>
</tr>
<tr>
<td class="label">K27</td>
<td>DNA damage response</td>
</tr>
<tr>
<td class="label">K33</td>
<td>Mitochondrial quality control</td>
</tr>
<tr>
<td class="label">K29</td>
<td>Lysosomal degradation</td>
</tr>
<tr>
<td class="label">K6</td>
<td>Mitochondrial dynamics</td>
</tr>
<tr>
<td class="label">M1 (linear)</td>
<td>[NF-κB](/entities/nf-kb) signaling</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer-disease" style="color:#ef9a9a">ALZHEIMER DISEASE</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">AMYOTROPHIC LATERAL SCLEROSIS</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2864 edges</a></td>
</tr>
</table>

...

Ubiquitin

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Ubiquitin</th>
</tr>
<tr>
<td class="label">Linkage</td>
<td>Function</td>
</tr>
<tr>
<td class="label">K48</td>
<td>Proteasomal degradation</td>
</tr>
<tr>
<td class="label">K63</td>
<td>Endocytosis, signaling, [autophagy](/entities/autophagy)</td>
</tr>
<tr>
<td class="label">K11</td>
<td>Cell cycle regulation</td>
</tr>
<tr>
<td class="label">K27</td>
<td>DNA damage response</td>
</tr>
<tr>
<td class="label">K33</td>
<td>Mitochondrial quality control</td>
</tr>
<tr>
<td class="label">K29</td>
<td>Lysosomal degradation</td>
</tr>
<tr>
<td class="label">K6</td>
<td>Mitochondrial dynamics</td>
</tr>
<tr>
<td class="label">M1 (linear)</td>
<td>[NF-κB](/entities/nf-kb) signaling</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer-disease" style="color:#ef9a9a">ALZHEIMER DISEASE</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">AMYOTROPHIC LATERAL SCLEROSIS</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2864 edges</a></td>
</tr>
</table>

Ubiquitin is a highly conserved 76-amino acid protein that covalently attaches to target proteins to mark them for various cellular fates.[@overview2014][@impairment2016] This post-translational modification, called ubiquitination or ubiquitylation, is a fundamental regulatory mechanism controlling protein degradation, signaling, trafficking, and localization. Dysregulation of ubiquitin biology is central to many neurodegenerative diseases.

Structure and Biochemistry

Ubiquitin Molecule

Molecular weight: 8.5 kDa
Seven lysine residues (K6, K11, K27, K29, K33, K48, K63)
N-terminal methionine (M1)
C-terminal glycine (G76) for conjugation

E1-E2-E3 Enzymatic Cascade

E1 - Activating enzymes:

~2 enzymes in humans
ATP-dependent ubiquitin activation
Forms thioester bond with ubiquitin C-terminus

E2 - Conjugating enzymes:

~40 enzymes in humans
Receive ubiquitin from E1
Determine chain linkage type

E3 - Ligase enzymes:

>600 enzymes in humans
Substrate recognition
Transfer ubiquitin to target proteins

Ubiquitin Chain Types

Homotypic Chains (Same Linkage)

Heterotypic Chains

Mixed linkage chains
Branched ubiquitin chains
More complex regulatory functions

The Ubiquitin-Proteasome System (UPS)

26S Proteasome Structure

20S core particle (α-rings + β-rings)
19S regulatory caps (6 ATPases)
Recognizes poly-K48 chains
Degrades ubiquitinated proteins

Degradation Process

Polyubiquitin chain recognition

Substrate unfolding

Translocation into 20S core

Proteolytic cleavage (β1, β2, β5)

Peptide release

Autophagy-Lysosome Pathway

Ubiquitin in Autophagy

Selective autophagy receptors (p62, OPTN, NDP52)
Recognize poly-K63 and K27 chains
Link cargo to autophagosomes
LC3 interaction domain (LIR)

Aggrephagy

Clearance of protein aggregates
p62/SQSTM1 as key receptor
Ubiquitin chain specificity
Impaired in neurodegeneration

Disease Relevance

Alzheimer's Disease

Ubiquitinated [tau](/proteins/tau) tangles[@taudriven2017]
Impaired proteasome function
p62 accumulation in plaques
Failed aggregate clearance
[UPS](/mechanisms/ubiquitin-proteasome-system) dysfunction precedes symptoms

Parkinson's Disease

LRRK2 mutations affect ubiquitination
Parkin E3 ligase dysfunction
PINK1-Parkin mitophagy impairment
Ubiquitinated Lewy bodies
G2019S LRRK2 alters autophagy

Amyotrophic Lateral Sclerosis

Ubiquitinated inclusions
Mutations in UBQLN2 (ubiquilin 2)
[TDP-43](/mechanisms/tdp-43-proteinopathy) ubiquitination
Proteasome impairment
Autophagy dysfunction

Huntington's Disease

Mutant [huntingtin](/proteins/huntingtin) aggregates
Impaired UPS function
Ubiquitinated inclusion bodies
Autophagy compensation
Therapeutic targeting potential

Frontotemporal Dementia

Tau and TDP-43 pathology
Ubiquitin chain abnormalities
OPTN mutations
p62 accumulation

Quality Control Mechanisms

ER-Associated Degradation (ERAD)

Misfolded proteins in ER
Retrotranslocation
Ubiquitination by E3 ligases
Proteasomal degradation

Mitochondrial Quality Control

PINK1-Parkin mitophagy
Ubiquitin chains on mitochondria
Autophagy receptor recruitment
Mitochondrial dynamics

Nuclear Quality Control

Proteasomal degradation in nucleus
Chromatin-associated degradation
Histone ubiquitination

Therapeutic Approaches

Proteasome Enhancement

Natural compounds (EGCG, curcumin)
Proteasome activators
Overcoming inhibition

Autophagy Induction

[mTOR](/mechanisms/mtor-signaling-pathway) inhibitors (rapamycin)
Trehalose
Exercise
Caloric restriction

E3 Ligase Modulation

Small molecule modulators
Gene therapy approaches
Specific ligase targeting

Deubiquitinating Enzymes (DUBs)

USP14 inhibition
OTUB1 enhancement
Proteasome-associated DUBs

Biomarkers

Protein Aggregation Markers

Ubiquitinated proteins in CSF
p62 levels
Serum ubiquitin

Activity Measures

Proteasome activity assays
Autophagic flux
Ubiquitin chain analysis

External Links

[UniProt: ubiquitin](https://www.uniprot.org/)
[PubMed: ubiquitin](https://pubmed.ncbi.nlm.nih.gov/?term=ubiquitin+neurodegeneration)

References

[Unknown, Overview of the ubiquitin-proteasome system (2014)](https://pubmed.ncbi.nlm.nih.gov/25092124/)

[Unknown, Impairment of the ubiquitin-proteasome system in Alzheimer's diseases and other tauopathies (2016)](https://pubmed.ncbi.nlm.nih.gov/26732485/)

[Unknown, Tau-driven ubiquitination and neurodegeneration (2017)](https://doi.org/10.1186/s40478-017-0463-3)

Pathway Diagram

The following diagram shows key molecular relationships for Ubiquitin based on knowledge graph edges:

Mermaid diagram (expand to render)

Pathway Diagram

The following diagram shows the key molecular relationships involving Ubiquitin discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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Related Entities

UBIQUITIN

▸Metadataorigin_type: v1_polymorphic_backfill

slug	proteins-ubiquitin
kg_node_id	UBIQUITIN
entity_type	protein
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-b9c0d00e2d02
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'proteins-ubiquitin'}
_schema_version	1

📊 Evidence Profile Foundational

Evidence Balance

+0%

Certainty

100%

Debates

0

Incoming

167

Outgoing

141

0 supporting 0 contradicting 0 neutral

View full evidence profile →

Public annotations (0)Annotate on Hypothes.is →

No public annotations yet.

📗 Cite This Artifact

Ubiquitin

Ubiquitin

Overview

Ubiquitin

Overview

Structure and Biochemistry

Ubiquitin Molecule

E1-E2-E3 Enzymatic Cascade

Ubiquitin Chain Types

Homotypic Chains (Same Linkage)

Heterotypic Chains

The Ubiquitin-Proteasome System (UPS)

26S Proteasome Structure

Degradation Process

Autophagy-Lysosome Pathway

Ubiquitin in Autophagy

Aggrephagy

Disease Relevance

Alzheimer's Disease

Parkinson's Disease

Amyotrophic Lateral Sclerosis

Huntington's Disease

Frontotemporal Dementia

Quality Control Mechanisms

ER-Associated Degradation (ERAD)

Mitochondrial Quality Control

Nuclear Quality Control

Therapeutic Approaches

Proteasome Enhancement

Autophagy Induction

E3 Ligase Modulation

Deubiquitinating Enzymes (DUBs)

Biomarkers

Protein Aggregation Markers

Activity Measures

See Also

External Links

References

Pathway Diagram

Pathway Diagram

💬 Discussion