DNA Ligase III Protein

DNA Ligase III Protein

Introduction

Dna Ligase Iii Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#f0f0f0;">DNA Ligase III</th></tr>
<tr><td><strong>Protein Name</strong></td><td>DNA Ligase 3</td></tr>
<tr><td><strong>Gene</strong></td><td>[LIG3](/genes/lig3)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P18858](https://www.uniprot.org/uniprot/P18858)</td></tr>
<tr><td><strong>PDB IDs</strong></td><td>1T15, 3FC8, 5U07</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>110 kDa (nuclear), 95 kDa (mitochondrial)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Nucleus, Mitochondria</td></tr>
<tr><td><strong>Protein Family</strong></td><td>DNA ligase family</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2 edges</a></td>
</tr>
</table>
</div>

Overview

DNA Ligase III is a specialized DNA ligase that functions in multiple DNA repair pathways, including base excision repair (BER) and mitochondrial DNA repair. It is unique among DNA ligases for its dual localization to both the nucleus and mitochondria.

Structure

DNA Ligase III Protein

Introduction

Dna Ligase Iii Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#f0f0f0;">DNA Ligase III</th></tr>
<tr><td><strong>Protein Name</strong></td><td>DNA Ligase 3</td></tr>
<tr><td><strong>Gene</strong></td><td>[LIG3](/genes/lig3)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P18858](https://www.uniprot.org/uniprot/P18858)</td></tr>
<tr><td><strong>PDB IDs</strong></td><td>1T15, 3FC8, 5U07</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>110 kDa (nuclear), 95 kDa (mitochondrial)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Nucleus, Mitochondria</td></tr>
<tr><td><strong>Protein Family</strong></td><td>DNA ligase family</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2 edges</a></td>
</tr>
</table>
</div>

Overview

DNA Ligase III is a specialized DNA ligase that functions in multiple DNA repair pathways, including base excision repair (BER) and mitochondrial DNA repair. It is unique among DNA ligases for its dual localization to both the nucleus and mitochondria.

Structure

Domain Architecture

• N-terminal BRCT Domain: Protein-protein interactions, XRCC1 binding (nuclear isoform)
• NAD-dependent DNA Ligase Domain: Catalytic core
• OB-fold Domain: DNA binding
• C-terminal Zinc Finger: Protein interaction

Isoforms

• DNA Ligase III-α: Nuclear isoform (~110 kDa), interacts with XRCC1
• DNA Ligase III-β: Testis-specific isoform
• Mitochondrial isoform: Alternative translation initiation (~95 kDa)

Structural Features

• ATP-dependent ligase
• Conserved adenylation domain
• Single-stranded DNA binding activity
• XRCC1 interaction through BRCT domain

Normal Function

Base Excision Repair (BER)

• Final step in nick sealing after base removal
• Works with XRCC1 scaffold protein
• Essential for repair of oxidative DNA damage

Single-Strand Break Repair

• Completes repair of SSBs
• Works with PARP1 and XRCC1
• Rapid response to endogenous DNA damage

Mitochondrial DNA Maintenance

• Essential for mtDNA repair
• Required for mtDNA replication
• Maintains mitochondrial genome integrity

Nuclear Functions

• Alternative NHEJ pathway
• Replication-related DNA repair
• Cell cycle regulation

Role in Disease

Alzheimer's Disease

DNA ligase III plays a critical role in neuronal DNA repair, and its dysfunction contributes to Alzheimer's disease (AD) pathogenesis. Neurons are particularly vulnerable to oxidative stress due to their high metabolic rate and post-mitotic state. The accumulation of oxidative DNA damage in AD brain correlates with impaired DNA repair capacity, and LIG3 is specifically oxidized in AD neurons, compromising its catalytic activity[@kuksal2017]. Studies have shown that DNA ligase III deficiency in neurons leads to DNA repair defects that phenocopy key features of AD, including synaptic loss, cognitive decline, and neuronal death[@ahmed2018]. The Base Excision Repair (BER) pathway, which LIG3 participates in, is the primary mechanism for repairing oxidative DNA damage in the brain. Impairment of this pathway contributes to the accumulation of toxic DNA lesions that drive neurodegeneration.

Parkinson's Disease

In Parkinson's disease (PD), LIG3 is implicated in the repair of mitochondrial DNA damage induced by environmental toxins and endogenous oxidative stress. The dopaminergic neurons of the substantia nigra are particularly susceptible to mitochondrial dysfunction, and LIG3-mediated mitochondrial DNA repair is essential for their survival[@choudhury2020]. Studies using PD models have shown that enhancing DNA repair capacity can protect neurons from toxin-induced cell death. LIG3's dual localization to both nucleus and mitochondria makes it uniquely positioned to maintain genomic integrity in dopaminergic neurons.

Aging and neurodegeneration

The aging brain shows progressive decline in DNA repair capacity, and LIG3 dysfunction may contribute to age-related neurodegeneration[@mccann2019]. Mitochondrial DNA damage accumulates with age, and LIG3's role in mitochondrial DNA maintenance becomes increasingly important. The NAD+-dependent deacetylase SIRT1 has been shown to regulate LIG3 function, linking DNA repair to cellular energy metabolism and the aging process.

Cancer and Neurodegeneration: Opposite Effects

Interestingly, LIG3 has opposing roles in cancer and neurodegeneration. While LIG3 deficiency promotes tumorigenesis due to genomic instability, it also sensitizes cells to DNA damage-induced cell death—a property exploited in cancer therapy with PARP inhibitors. This duality makes LIG3 a challenging therapeutic target. In neurons, however, maintaining LIG3 function is protective against age-related DNA damage accumulation.

Therapeutic Targeting

PARP Inhibitors

Synthetic lethality between LIG3 deficiency and PARP inhibition has been extensively studied in cancer therapy. However, for neurodegenerative diseases, the goal is to enhance rather than inhibit LIG3 function. PARP inhibitors can actually be detrimental in neurons by preventing DNA repair[@cana2015], highlighting the need for selective approaches.

Gene Therapy Approaches

Gene therapy to deliver functional LIG3 to neurons represents a potential therapeutic strategy for AD and PD. Viral vector-mediated LIG3 expression has shown promise in preclinical models, improving neuronal survival under oxidative stress conditions.

Small Molecule Activators

Identification of small molecules that enhance LIG3 catalytic activity or stability is an active area of research. Compounds that increase LIG3 expression or improve its recruitment to damaged DNA sites could have therapeutic utility.

Mitochondria-Targeted Strategies

Given the importance of mitochondrial LIG3 in neuronal survival, mitochondria-targeted approaches are particularly promising. Mitochondrial-targeted antioxidants may help protect LIG3 from oxidative inactivation, while compounds that enhance mitochondrial DNA repair could provide neuroprotection.

See Also

• [LIG3 Gene](/genes/lig3)
• [DNA Repair Mechanisms](/mechanisms/dna-repair-neurodegeneration)
• [Base Excision Repair](/mechanisms/base-excision-repair)
• [Mitochondrial DNA](/entities/mitochondrial-dna)
• [XRCC1 Gene](/genes/xrcc1)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

References