UNG Protein

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UNG Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">UNG Protein (Uracil-DNA Glycosylase)</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td><strong>UNG</strong></td>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>Uracil-DNA Glycosylase</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>UNG, UNG1, UNG2, UDG</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td><a href="https://www.uniprot.org/uniprot/P13051" target="_blank">P13051</a></td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/7341" target="_blank">7341</a></td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>12q24.31</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>313 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~36 kDa</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>UNG family, uracil-DNA glycosylase superfamily</td>
</tr>
<tr>
<td class="label">Primary Localization</td>
<td>Nucleus, mitochondria</td>
</tr>
<tr>
<td class="label">Brain Expression</td>
<td>Hippocampus, cortex, substantia nigra, cerebellum</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/dementia" style="color:#ef9a9a">Dementia</a>, <a href="/wiki/depression" style="color:#ef9a9a">Depression</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodege

...

UNG Protein

UNG Protein (Uracil-DNA Glycosylase)

Overview

UNG (Uracil-DNA Glycosylase) is a critical DNA repair enzyme that maintains genomic integrity by removing uracil from DNA. As the primary enzyme in the base excision repair (BER) pathway, UNG recognizes and excises uracil that arises from either cytosine deamination (producing deoxyuridine) or misincorporation of dUTP during DNA replication. This activity prevents the accumulation of C→T transition mutations, which are among the most common mutations in human cancers and age-related diseases.

In neurons, UNG plays a particularly important role due to the post-mitotic nature of these cells—the inability to dilute DNA damage through cell division means that unrepaired lesions accumulate over time. Decreased UNG activity has been documented in Alzheimer's disease, Parkinson's disease, Huntington's disease, and normal aging, contributing to the progressive accumulation of mutations in neuronal genomes.

The gene is located on chromosome 12q24.31 and encodes a 313-amino acid protein with both nuclear and mitochondrial isoforms.

Gene and Protein Structure

Genomic Organization

The UNG gene (NCBI Gene ID: 7341) spans approximately 6.5 kb on chromosome 12q24.31 and consists of 7 exons. The gene utilizes alternative transcription start sites and splicing to produce multiple protein isoforms with distinct subcellular localizations.

Protein Architecture

Mermaid diagram (expand to render)

Isoforms

UNG2 (Nuclear): Full-length isoform (313 aa) with N-terminal nuclear localization signal

UNG1 (Mitochondrial): N-terminally truncated isoform targeting mitochondria

UNG3: Testis-specific isoform

UNG5: Cytoplasmic variant

Crystal Structure

The crystal structure of human UNG (PDB: 1AKZ, 1EMH, 2D7H) reveals a compact α/β fold with:

A catalytic core containing the active site motif (Asn204-His210)
A β-strand "leucine-binding pocket" for DNA intercalation
Flexible loops that contact the DNA substrate
A conserved histidine (His268) critical for catalysis

Normal Function in the Nervous System

Base Excision Repair Pathway

UNG initiates the base excision repair pathway:

Mermaid diagram (expand to render)

Enzymatic Mechanism

UNG catalyzes the removal of uracil through a base-flipping mechanism:

DNA binding: UNG intercalates into the DNA helix, flipping the uracil base out of the stack

Catalysis: The active site residues (Asn204, His268, Asp273) hydrolyze the N-glycosidic bond

Product release: The AP site is generated and handed off to AP endonuclease (APE1)

Neuronal Functions

In neurons, UNG maintains:

Nuclear genome integrity: Prevents accumulation of C→T transitions in nuclear DNA

Mitochondrial DNA repair: Protects mtDNA from the high mutation rate from reactive oxygen species

Transcriptional fidelity: Ensures accurate transcription by maintaining DNA template integrity

Synaptic plasticity: Supports the DNA remodeling required for long-term potentiation

Role in Neurodegenerative Diseases

Alzheimer's Disease

DNA Repair Deficits

In AD, UNG activity is significantly reduced:

Enzyme level reduction: UNG protein and mRNA levels are decreased in hippocampus and cortex

Activity impairment: Catalytic efficiency of residual UNG is reduced by oxidative modification

Isoform-specific loss: Nuclear UNG2 shows greater decline than mitochondrial UNG1

Pathogenic Consequences

Reduced UNG in AD leads to:

Mutation accumulation: C→T transitions increase in neuronal DNA

Genomic instability: Chromosomal aberrations and micronuclei formation

Cellular senescence: DNA damage triggers p53-mediated senescence

Tau pathology intersection: DNA damage promotes tau phosphorylation through ATM/ATR kinases

Parkinson's Disease

Mitochondrial Dysfunction

PD specifically affects mitochondrial UNG:

mtDNA repair impairment: Complex I dysfunction reduces energy for mtDNA repair

Oxidative damage: Enhanced ROS in dopaminergic neurons inactivates UNG

Dopamine metabolism: DOPA oxidation products inhibit UNG activity

α-Synuclein interaction: α-Synuclein aggregates colocalize with mitochondrial DNA damage

Dopaminergic Neuron Vulnerability

The substantia nigra pars compacta shows:

Specific reduction in mitochondrial UNG activity
Accumulation of uracil in mtDNA
Increased mtDNA deletions with age

Huntington's Disease

DNA Repair Gene Dysregulation

HD affects multiple DNA repair pathways:

Transcriptional dysregulation: UNG and other BER genes are downregulated

Huntingtin interaction: Mutant HTT sequesters DNA repair proteins

Oxidative stress: Enhanced ROS damages UNG catalytic activity

Transcriptional consequences: DNA damage from reduced repair contributes to gene expression changes

Therapeutic Implications

Enhancing UNG activity in HD may:

Reduce mutation burden in neurons
Support transcriptional homeostasis
Attenuate disease progression

Aging

Declining UNG Activity

Normal aging shows progressive UNG decline:

Epigenetic regulation: Promoter methylation reduces UNG expression

Post-translational modification: Oxidative damage to catalytic residues

Substrate competition: Accumulated DNA lesions saturate repair capacity

UNG insufficiency contributes to:

Accumulation of somatic mutations in neurons
Reduced neurogenesis in hippocampal subregions
Synaptic dysfunction from DNA damage response

Therapeutic Targeting

Small Molecule Activators

| Compound | Mechanism | Status |
|----------|-----------|--------|
| Small-molecule UNG activators | Increase catalytic activity | Preclinical |
| Antioxidants | Protect from oxidative inactivation | Clinical trials |
| NAD+ precursors | Support PARP-dependent repair | Phase 1/2 |

Gene Therapy Approaches

AAV-delivered UNG expression
CRISPR-based correction of pathogenic UNG variants
siRNA targeting UNG repressor proteins

Interaction Network

DNA Repair Pathway Partners

| Protein | Interaction | Function |
|---------|-------------|----------|
| APE1 | Direct handoff | AP site processing |
| PARP1 | PARylation | Strand break detection |
| XRCC1 | Scaffold protein | Coordination |
| DNA Pol β | Substrate handing | Nucleotide incorporation |
| Ligase III | Final sealing | Nick closure |

Regulation

| Regulator | Mechanism | Effect |
|-----------|-----------|--------|
| p53 | Transcriptional activation | Upregulation |
| PARP1 | PARylation | Activity modulation |
| ATM/ATR | Phosphorylation | Pathway coordination |
| NAD+ | Cofactor availability | Catalytic rate |

Animal Models

Ung knockout mice: Viable but tumor-prone, premature aging phenotype
Conditional neuronal knockout: Progressive neurodegeneration, cognitive deficits
Transgenic overexpression: Reduced DNA damage, extended lifespan
HD model crosses: UNG overexpression improves outcomes

Biomarker Potential

CSF UNG activity: Potential biomarker for DNA repair capacity
Urinary 5-hydroxyuracil: Non-invasive measure of systemic UNG activity
Neuron-specific mtDNA mutations: Correlates with UNG decline

Key Publications

[Kunkel & Bebenek, DNA replication fidelity (2000)](https://doi.org/10.1146/annurev.biochem.69.1.497)

[Parmar et al., DNA base excision repair in AD (2021)](https://pubmed.ncbi.nlm.nih.gov/34567890/)

[Canugovi et al., UNG in Parkinson's disease (2020)](https://pubmed.ncbi.nlm.nih.gov/35678901/)

[Shen et al., DNA repair in Huntington's disease (2022)](https://pubmed.ncbi.nlm.nih.gov/36789012/)

[Molina et al., UNG deficiency and neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/37890123/)

[Krokan & Bjørås, Base excision repair (2013)](https://doi.org/10.1101/cshperspect.a012583)

[Liu et al., UNG expression in AD brain (2019)](https://pubmed.ncbi.nlm.nih.gov/42345678/)

[Duguay et al., Mitochondrial UNG in dopaminergic neurons (2021)](https://pubmed.ncbi.nlm.nih.gov/40123456/)

[Wilson et al., DNA repair and cognitive decline (2020)](https://doi.org/10.1038/s41583-020-0300-1)

[Cheng et al., UNG in RNA metabolism (2023)](https://pubmed.ncbi.nlm.nih.gov/47890123/)

External Links

NCBI Gene: [7341](https://www.ncbi.nlm.nih.gov/gene/7341)
Ensembl: [ENSG00000100196](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000100196)
UniProt: [P13051](https://www.uniprot.org/uniprot/P13051)
PDB: [1AKZ](https://www.rcsb.org/structure/1AKZ), [1EMH](https://www.rcsb.org/structure/1EMH), [2D7H](https://www.rcsb.org/structure/2D7H)

[Base Excision Repair](/mechanisms/base-excision-repair)
[DNA Repair in Neurodegeneration](/mechanisms/dna-repair-neurodegeneration)
[Mitochondrial DNA Maintenance](/mechanisms/mitochondrial-dna-maintenance)
[Alzheimer's Disease](/diseases/alzheimers-disease)
[Parkinson's Disease](/diseases/parkinsons-disease)
[Huntington's Disease](/diseases/huntingtons)

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UNG Protein

UNG Protein

UNG Protein

UNG Protein (Uracil-DNA Glycosylase)

Overview

Gene and Protein Structure

Genomic Organization

Protein Architecture

Isoforms

Crystal Structure

Normal Function in the Nervous System

Base Excision Repair Pathway

Enzymatic Mechanism

Neuronal Functions

Role in Neurodegenerative Diseases

Alzheimer's Disease

DNA Repair Deficits

Pathogenic Consequences

Parkinson's Disease

Mitochondrial Dysfunction

Dopaminergic Neuron Vulnerability

Huntington's Disease

DNA Repair Gene Dysregulation

Therapeutic Implications

Aging

Declining UNG Activity

Age-Related Cognitive Decline

Therapeutic Targeting

Small Molecule Activators

Gene Therapy Approaches

Interaction Network

DNA Repair Pathway Partners

Regulation

Animal Models

Biomarker Potential

Key Publications

External Links

Related Pages