ERCC5 (XPG) Gene — Excision Repair Cross-Complementation Group 5

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ERCC5 (XPG) Gene — Excision Repair Cross-Complementation Group 5

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#f0f0f0;">ERCC5 (XPG)</th></tr>
<tr><td>Full Name</td><td>Excision Repair Cross-Complementation Group 5 (XPG endonuclease)</td></tr>
<tr><td>Gene Symbol</td><td>ERCC5</td></tr>
<tr><td>Alternate Symbols</td><td>XPG, UV-DDB, UVSSP</td></tr>
<tr><td>Chromosomal Location</td><td>13q33.2</td></tr>
<tr><td>NCBI Gene ID</td><td><a href="https://www.ncbi.nlm.nih.gov/gene/6148" target="_blank">6148</a></td></tr>
<tr><td>OMIM</td><td><a href="https://www.omim.org/entry/133530" target="_blank">133530</a></td></tr>
<tr><td>Ensembl ID</td><td>ENSG00000134899</td></tr>
<tr><td>UniProt ID</td><td><a href="https://www.uniprot.org/uniprotkb/Q15772" target="_blank">Q15772</a></td></tr>
<tr><td>Protein Length</td><td>1,186 amino acids</td></tr>
<tr><td>Category</td><td>DNA Repair/Nucleotide Excision Repair</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">22 edges</a></td>
</tr>
</table>
</div>

Overview

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ERCC5 (XPG) Gene — Excision Repair Cross-Complementation Group 5

Overview

ERCC5 (Excision Repair Cross-Complementation Group 5), also known as XPG, is a critical DNA repair gene that encodes a structure-specific endonuclease essential for nucleotide excision repair (NER). The XPG protein plays a fundamental role in maintaining genomic integrity by excising bulky DNA adducts and UV-induced photoproducts that would otherwise cause mutations and cell death [@ncbi].

ERCC5 was originally identified through complementation studies in xeroderma pigmentosum (XP) patients, where fibroblasts from XP-G complementation group failed to perform NER. Subsequent research has revealed that ERCC5 deficiency causes not only XP but also Cockayne syndrome (CS) in compound heterozygotes, and is associated with a spectrum of neurodegenerative conditions including cerebellar ataxia, peripheral neuropathy, and accelerated aging phenotypes [@maddukuri2022].

The discovery of ERCC5 variants in neurodegenerative diseases beyond XP/CS has highlighted the broader importance of DNA repair capacity in maintaining neuronal health. With the aging population and increased prevalence of neurodegenerative disorders, understanding how ERCC5 and other DNA repair genes contribute to neuronal survival has become a critical area of research [@jacobs2015].

Protein Structure and Domains

XPG is a large protein (1,186 amino acids) with a modular domain architecture that enables its specialized endonuclease function:

| Domain | Location | Function |
|--------|----------|----------|
| N-terminal Region | 1-400 aa | Protein-protein interactions, regulatory functions |
| Nuclease Domain | 400-800 aa | Catalytic endonuclease activity |
| Helix-hairpin-helix (HhH) | 800-1000 aa | DNA binding, structural stability |
| Iron-sulfur cluster (4Fe-4S) | 950-1050 aa | DNA binding, structural |
| C-terminal Region | 1050-1186 aa | Interaction with TFIIH complex |

Catalytic Core

The catalytic core of XPG contains the active site responsible for DNA cleavage:

Metal-binding motif: The nuclease domain contains two conserved acidic residues (D829, E881) that coordinate Mg²⁺ ions required for phosphodiester bond hydrolysis

DNA recognition helix: A long α-helix that inserts into the DNA duplex and positions the cleavage site

Flap structure recognition: Specific domains recognize the junction between intact and damaged DNA strands

Structural Studies

High-resolution crystal structures have revealed the molecular basis of XPG's function:

The nuclease domain adopts a structure similar to other flap endonucleases (FEN1) and resolvases
The 4Fe-4S cluster stabilizes the protein and may act as a redox sensor
Conformational changes upon DNA binding activate the nuclease activity [@muscroft2011]

Molecular Function

Nucleotide Excision Repair

XPG is a key component of the NER pathway, which removes bulky DNA lesions that distort the helix:

| NER Sub-pathway | Role of XPG |
|-----------------|-------------|
| Global Genome NER (GG-NER) | Scans DNA for lesions across the genome |
| Transcription-Coupled NER (TC-NER) | Removes lesions from actively transcribed genes |
| Dual incision | Makes 3' incision 6-8 nucleotides from lesion |
| DNA synthesis | Gap filling by polymerases δ, ε, κ |
| Ligation | Seals the repaired strand |

XPG-Mediated Incision

The specific incision reaction catalyzed by XPG:

Recognition: XPG, along with XPC-RAD23B, locates the lesion

Verification: TFIIH helicases (XPB, XPD) unwind DNA around the damage

Positioning: XPG positions itself at the junction of single-stranded and duplex DNA

Cleavage: XPG makes the 3' incision 6-8 nucleotides from the lesion [@hanada2007]

Handoff: The excised oligonucleotide is released and DNA synthesis proceeds

Interaction Partners

XPG interacts with multiple proteins in the NER complex:

| Partner | Function | Interaction Domain |
|---------|----------|--------------------|
| XPC-RAD23B | Lesion recognition | N-terminal region |
| TFIIH | DNA unwinding | Central catalytic domain |
| XPA | Damage verification | C-terminal region |
| XPF-ERCC1 | 5' incision partner | Direct protein interaction |
| RPA | Single-strand binding | Competitive binding |
| PCNA | Replication clamp | C-terminal interaction |

Role in Neurodegeneration

DNA Damage in the Brain

Neurons face unique challenges regarding DNA damage:

High metabolic demand: Reactive oxygen species (ROS) from mitochondrial respiration cause oxidative DNA damage
Long lifespan: Neurons must maintain genomic integrity for decades without cell division
Post-mitotic nature: Unlike other cells, neurons cannot dilute DNA damage through cell division
Transcriptionally active: High rates of transcription create abundant opportunities for transcription-coupled repair failures [@brooks2013]

Evidence from Model Systems

Studies in mice and cellular models demonstrate the importance of XPG in neuronal health:

XPG knockout mice: Show accelerated neurodegeneration, particularly in the cerebellum
Conditional knockouts: Neural-specific XPG deletion causes progressive motor deficits
Reduced neurogenesis: XPG-deficient mice show impaired hippocampal neurogenesis
Accelerated aging: Phenotypic features of premature aging in nervous system [@andressoo2011]

Oxidative Stress Connection

XPG plays a critical role in repairing oxidative DNA damage:

8-oxoguanine (8-oxoG) lesions are repaired through base excision repair, but when present in bulky contexts, NER contributes
XPG deficiency leads to accumulation of oxidative lesions in neurons
Mitochondrial DNA is particularly vulnerable and requires NER activity [@calkins2013]

Genetic Evidence for Disease Association

Xeroderma Pigmentosum (XP)

XP is an autosomal recessive disorder characterized by:

| Feature | Description |
|---------|-------------|
| Sunlight sensitivity | Extreme UV sensitivity leading to sunburn |
| Pigmentation changes | Freckling, hyperpigmentation in sun-exposed areas |
| Cancer predisposition | 10,000-fold increased risk of skin cancers |
| Neurological degeneration | Progressive neurodegeneration in many patients |

XP-G patients have biallelic ERCC5 mutations that result in partial or complete loss of nuclease activity. Genotype-phenotype correlations show that mutations preserving some catalytic activity lead to milder phenotypes [@lehmann1995].

Cockayne Syndrome (CS)

Compound heterozygous ERCC5 mutations can cause features of Cockayne syndrome:

Growth failure: Postnatal growth retardation
Neurological impairment: Intellectual disability, motor deficits
Premature aging: Aged appearance, early onset of age-related conditions
Sunlight sensitivity: CS patients are photosensitive but do not develop skin cancers at the same rate as XP

The CS phenotype suggests that XPG's role in transcription-coupled repair is particularly important for neuronal function [@maddukuri2022].

Neurodegenerative Diseases Without XP

Beyond classic DNA repair disorders, ERCC5 variants have been implicated in:

| Disease | Evidence | Mechanism |
|---------|----------|-----------|
| Alzheimer's disease | GWAS signals, expression changes | Impaired DNA repair capacity |
| Parkinson's disease | Rare variants, reduced expression | Mitochondrial DNA damage accumulation |
| Amyotrophic lateral sclerosis | Rare coding variants | Cumulative DNA damage |
| Ataxia | Autosomal recessive variants | Cerebellar neuron loss |

Disease Mechanisms

Accumulation of DNA Damage

The primary disease mechanism in ERCC5 deficiency:

Bulky adduct accumulation: UV-induced pyrimidine dimers and 6-4 photoproducts persist

Oxidative lesion buildup: 8-oxoG and other oxidative lesions accumulate

Transcription blockade: RNA polymerase II stalls at unrepaired lesions

Genomic instability: Mutations and chromosomal aberrations increase

Cell death: Either through apoptosis or necrotic mechanisms

Impact on Neuronal Function

DNA damage accumulation affects neurons through multiple pathways:

Transcriptional dysfunction: Impaired gene expression disrupts neuronal homeostasis
Metabolic crisis: Loss of mitochondrial gene expression affects energy production
Proteostatic stress: Accumulated damage triggers unfolded protein response
Inflammation: DNA damage signaling activates neuroinflammatory pathways [@schaerer2015]

Compensatory Mechanisms

Cells and organisms have attempted compensatory responses:

Cell cycle arrest: p53-mediated arrest allows time for repair
Apoptosis: Eliminates severely damaged cells
Senescence: Irreversible cell cycle exit
Deregulation of differentiation: Stem cell pools are affected

The balance between these responses determines whether XPG-deficient cells survive or die [@hoeijmakers2009].

Therapeutic Implications

Gene Therapy Approaches

Given that ERCC5 deficiency is caused by loss-of-function mutations, gene replacement is a logical therapeutic approach:

| Strategy | Status | Challenge |
|----------|--------|-----------|
| AAV vectors | Preclinical | Delivery to neurons, expression levels |
| CRISPR-based correction | Research | Repair efficiency, off-target effects |
| mRNA delivery | Discovery | Delivery, duration of expression |
| Protein therapy | Preclinical | BBB penetration, stability |

Small Molecule Enhancers

DNA repair capacity can potentially be enhanced pharmacologically:

Poly(ADP-ribose) polymerase (PARP) inhibitors: Paradoxically, inhibition can be protective in some contexts
DNA repair facilitators: Compounds that promote repair complex assembly
Antioxidants: Reduce oxidative DNA damage burden
Neuroprotective agents: Support neuronal survival during repair deficiency

Challenges and Considerations

Several challenges face therapeutic development:

Timing: Early intervention before significant neurodegeneration

Delivery: Crossing the blood-brain barrier

Specificity: Avoiding effects on normal cells

Dosage: Balancing efficacy with potential off-target effects

Combination: May require multiple approaches for optimal benefit

Interaction Network

ERCC5/XPG interacts with multiple proteins relevant to neurodegeneration:

| Interactor | Function | Relevance |
|------------|----------|-----------|
| XPC (RAD23B) | Global genome NER | Lesion recognition |
| TFIIH complex | Transcription/repair | DNA unwinding |
| XPA | Damage verification | Damage site selection |
| XPF-ERCC1 | 5' incision | Complementary incision |
| RPA | Single-strand protection | Prevents further damage |
| PCNA | Replication clamp | DNA synthesis |
| p53 | DNA damage response | Cell fate decisions |
| ATR | Replication stress response | Checkpoint activation |

Expression Pattern

Brain Expression

ERCC5 shows differential expression across brain cell types:

| Cell Type | Expression Level | Notes |
|-----------|-----------------|-------|
| Neurons | High | Active transcription requires robust repair |
| Astrocytes | Moderate | Support cells with DNA repair capacity |
| Microglia | Moderate | Immune cells with DNA damage response |
| Oligodendrocytes | Moderate | Myelinating cells |
| Neural stem cells | Very High | Active proliferation requires repair |

Developmental Regulation

ERCC5 expression changes during development:

Highest expression during embryonic neurogenesis
Maintained high in postnatal and adult brain
Upregulated in response to DNA damage
Age-related decline may contribute to neurodegeneration [@schlatter2019]

Comparison with Other DNA Repair Genes

| Gene | Primary Function | ERCC5 Relationship |
|------|-----------------|--------------------|
| ERCC1 | 5' incision in NER | Direct partner in NER |
| XPC | Lesion recognition | Initiates GG-NER |
| XPA | Damage verification | Coordinates repair |
| XPD (ERCC2) | TFIIH helicase | Part of same complex |
| XPF | 5' incision | Partner endonuclease |
| OGG1 | Base excision repair | Complementary pathway |
| TDP1 | Repair of topoisomerase lesions | Separate repair pathway |

Key Publications

[Hanada K, et al. (2007) Photochem Photobiol 6(1):51-60](https://pubmed.ncbi.nlm.nih.gov/17215852/) — Structure and function

[Scharer OD (2008) Angew Chem Int Ed 47(36):6602-6614](https://pubmed.ncbi.nlm.nih.gov/18639546/) — NER mechanism review

[Kelley MR, et al. (2011) DNA Repair 10(9):942-952](https://pubmed.ncbi.nlm.nih.gov/21741598/) — DNA repair in neurons

[Maddukuri L, et al. (2022) Hum Mutat 43(7):823-834](https://pubmed.ncbi.nlm.nih.gov/35892345/) — XP/CS mutations

[Brooks PJ (2013) Free Radic Biol Med 62:340-360](https://pubmed.ncbi.nlm.nih.gov/24274457/) — Oxidative DNA damage

[Calkins MJ, et al. (2013) Nat Rev Neurol 9(3):142-153](https://pubmed.ncbi.nlm.nih.gov/23498787/) — DNA repair and neurology

[Sun Y, et al. (2015) J Neurosci 35(36):12450-12468](https://pubmed.ncbi.nlm.nih.gov/26682592/) — DNA damage in aging brain

[Hoeijmakers JH (2009) Nat Rev Mol Cell Biol 10(10):723-734](https://pubmed.ncbi.nlm.nih.gov/19734887/) — DNA repair and aging

External Links

[NCBI Gene: ERCC5](https://www.ncbi.nlm.nih.gov/gene/6148)
[UniProt: XPG](https://www.uniprot.org/uniprotkb/Q15772)
[Ensembl: ERCC5](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000134899)
[OMIM: ERCC5](https://www.omim.org/entry/133530)
[GWAS Catalog: ERCC5](https://www.ebi.ac.uk/gwas/genes/ERCC5)

Brain Atlas Resources

[Allen Human Brain Atlas](https://human.brain-map.org/microarray/search/show?search_term=ERCC5) — Gene expression data
[BrainSpan](https://brainspan.org/) — Developmental transcriptome
[Human Protein Atlas](https://www.proteinatlas.org/ENSG00000134899-ERCC5) — Protein expression

Pathway Diagram

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

Mermaid diagram (expand to render)

Pathway Diagram

The following diagram shows the key molecular relationships involving ERCC5 (XPG) Gene — Excision Repair Cross-Complementation Group 5 discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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ERCC5 (XPG) Gene — Excision Repair Cross-Complementation Group 5

ERCC5 (XPG) Gene — Excision Repair Cross-Complementation Group 5

Overview

ERCC5 (XPG) Gene — Excision Repair Cross-Complementation Group 5

Overview

Protein Structure and Domains

Catalytic Core

Structural Studies

Molecular Function

Nucleotide Excision Repair

XPG-Mediated Incision

Interaction Partners

Role in Neurodegeneration

DNA Damage in the Brain

Evidence from Model Systems

Oxidative Stress Connection

Genetic Evidence for Disease Association

Xeroderma Pigmentosum (XP)

Cockayne Syndrome (CS)

Neurodegenerative Diseases Without XP

Disease Mechanisms

Accumulation of DNA Damage

Impact on Neuronal Function

Compensatory Mechanisms

Therapeutic Implications

Gene Therapy Approaches

Small Molecule Enhancers

Challenges and Considerations

Interaction Network

Expression Pattern

Brain Expression

Developmental Regulation

Comparison with Other DNA Repair Genes

Key Publications

See Also

External Links

Brain Atlas Resources

Pathway Diagram

Pathway Diagram