TYDP1 — Tyrosyl-DNA Phosphodiesterase 1

TYDP1 — Tyrosyl-DNA Phosphodiesterase 1

Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">TYDP1 — Tyrosyl-DNA Phosphodiesterase 1</th>
</tr>
<tr>
<td class="label">Feature</td>
<td>TDP1</td>
</tr>
<tr>
<td class="label">Gene</td>
<td>TYDP1</td>
</tr>
<tr>
<td class="label">Substrate</td>
<td>Removes TOP1 from 3'-end</td>
</tr>
<tr>
<td class="label">Mechanistic class</td>
<td>Phosphodiesterase</td>
</tr>
<tr>
<td class="label">Metal dependency</td>
<td>Requires Mg2+/Mn2+</td>
</tr>
<tr>
<td class="label">Disease linkage</td>
<td>SCAN1 (ataxia)</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

TYDP1 (Tyrosyl-DNA Phosphodiesterase 1) is a gene located on chromosome 14q32.12 that encodes TDP1, a specialized DNA repair enzyme that catalyzes the removal of stalled topoisomerase I (TOP1) cleavage complexes (TOP1cc) from DNA. TOP1cc are covalent protein-DNA adducts where TOP1 remains covalently bound to the 3'-end of a DNA break, blocking DNA replication and transcription until removed[@zhou2015][@das2014].

TYDP1 — Tyrosyl-DNA Phosphodiesterase 1

Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">TYDP1 — Tyrosyl-DNA Phosphodiesterase 1</th>
</tr>
<tr>
<td class="label">Feature</td>
<td>TDP1</td>
</tr>
<tr>
<td class="label">Gene</td>
<td>TYDP1</td>
</tr>
<tr>
<td class="label">Substrate</td>
<td>Removes TOP1 from 3'-end</td>
</tr>
<tr>
<td class="label">Mechanistic class</td>
<td>Phosphodiesterase</td>
</tr>
<tr>
<td class="label">Metal dependency</td>
<td>Requires Mg2+/Mn2+</td>
</tr>
<tr>
<td class="label">Disease linkage</td>
<td>SCAN1 (ataxia)</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

TYDP1 (Tyrosyl-DNA Phosphodiesterase 1) is a gene located on chromosome 14q32.12 that encodes TDP1, a specialized DNA repair enzyme that catalyzes the removal of stalled topoisomerase I (TOP1) cleavage complexes (TOP1cc) from DNA. TOP1cc are covalent protein-DNA adducts where TOP1 remains covalently bound to the 3'-end of a DNA break, blocking DNA replication and transcription until removed[@zhou2015][@das2014].

TDP1 is critical for maintaining genomic integrity, particularly in post-mitotic neurons that cannot use cell division to resolve DNA-protein crosslinks. Mutations in TYDP1 cause a recessively inherited neurodegenerative disease with features resembling early-onset [Parkinson's disease](/diseases/parkinsons-disease), including gait disturbance, dysarthria, and cognitive decline. TDP1 dysfunction also contributes to the pathogenesis of sporadic [Alzheimer's disease](/diseases/alzheimers-disease) and [Parkinson's disease](/diseases/parkinsons-disease) through impaired clearance of TOP1cc in neurons[@corti2013][@huang2018].

The TDP1 protein (~608 amino acids, ~68.5 kDa) is a member of the phosphodiesterase (PDE) family and contains a PINc-like (PilT N-terminus) nuclease domain that catalyzes the hydrolysis of the phosphodiester bond linking TOP1 to the DNA 3'-phosphate[@liu2017].

Gene and Protein Structure

Gene Architecture

The TYDP1 gene spans approximately 24 kb on chromosome 14q32.12 and consists of 14 exons. The gene encodes the TDP1 protein with a molecular weight of approximately 68.5 kDa.

Protein Structure and Catalytic Mechanism

TDP1 contains:

• N-terminal PINc domain (residues 1-500): The catalytic nuclease domain with a beta-helix barrel structure containing four conserved acidic residues (D275, E277, H394, H423) that coordinate two metal ions (Mg2+ or Mn2+) for catalysis.
• C-terminal region (residues 500-608): Regulatory region with proposed nuclear localization signal and protein-protein interaction motifs.

Relationship to TDP2

TDP1 and TDP2 (TYDP2/TTYH2) are the two known enzymes capable of removing topoisomerase-DNA complexes, but they have different substrate specificities and mechanisms:

Normal Biological Function

Topoisomerase I and Its Cleavage Complexes

TOP1 is an essential enzyme that relieves torsional DNA supercoiling by creating transient single-strand breaks. During its normal catalytic cycle:

However, in the presence of DNA damage (oxidative lesions, abasic sites, base mismatches) or Topoisomerase I inhibitors (camptothecin, irinotecan, topotecan), TOP1 can stall on DNA, creating TOP1 cleavage complexes (TOP1cc):

• TOP1 is covalently trapped on one strand while the other strand is broken
• The enzyme remains attached to the 3'-DNA end via a phosphotyrosyl bond
• These complexes block DNA replication, transcription, and fork progression

• Replication fork collapse → double-strand breaks
• Transcription stress → R-loop formation, RNA processing defects
• Genomic instability → chromosomal translocations, deletions

TDP1's Role in DNA Repair

TDP1 is the primary enzyme for removing TOP1 from the 3'-end of DNA[@das2014][@katyal2004]:

• TDP1 interacts with NER proteins including XPF-ERCC1 and CSB
• The NER machinery recognizes TOP1cc-stalled complexes
• TDP1 is recruited to remove TOP1 from the 3'-end
• NER then removes the remaining oligonucleotide containing the 5'-end TOP1

• In some contexts, TDP1 can remove TOP1 independently of NER
• This may be important in mitochondria (mitochondrial NER)

• Actively transcribed genes (on the non-template strand) are preferential targets of TOP1cc
• TC-NER specifically removes lesions from the transcribed strand
• TDP1 is part of the TC-NER response to TOP1cc in neurons

Mitochondrial DNA Repair

TDP1 is partially localized to mitochondria where it may participate in mitochondrial DNA (mtDNA) repair[@gomez2018]:

• mtDNA is particularly vulnerable to TOP1cc due to high replication rates and limited repair
• TDP1 may protect mtDNA from TOP1 inhibitor toxicity
• Mitochondrial TDP1 dysfunction leads to mtDNA deletions and point mutations
• Accumulated mtDNA mutations contribute to neuronal energy failure

Neuronal Relevance

[Neurons](/entities/neurons) are uniquely dependent on TDP1 because:

Disease Associations

TDP1-Related Neurodegeneration (SCAN1)

Mutations in TYDP1 cause Spinocerebellar Ataxia with Axonal Neuropathy type 1 (SCAN1), an autosomal recessive neurodegenerative disorder mapped to chromosome 14q32.12[@corti2013][@takahashi2017]:

Clinical Features:

• Age of onset: Typically 10-20 years (range: 6-30 years)
• Ataxia: Progressive gait and limb ataxia, due to cerebellar and peripheral nerve involvement
• Oculomotor apraxia: Difficulty initiating voluntary eye movements
• Retinopathy: Peripheral visual field loss, pigmentary retinopathy
• Seizures: Present in ~40% of patients
• Cognitive decline: Variable, ranging from mild impairment to frank dementia
• Peripheral neuropathy: Axonal sensorimotor neuropathy, loss of deep tendon reflexes
• Progression: Slowly progressive; patients become wheelchair-bound within 10-20 years of onset

• Autosomal recessive inheritance
• The most common pathogenic variant (H493R) has been identified in multiple families
• This variant has reduced catalytic activity (~30% of wild-type) but does not completely abolish function
• The phenotype is likely due to partial loss of TDP1 function rather than complete absence

• H493R mutation reduces TDP1's ability to process TOP1cc
• Accumulated TOP1cc block transcription in neurons
• Neuronal transcription stress leads to neurodegeneration
• The clinical overlap with ataxia-telangiectasia and other DNA repair disorders reflects the central role of TOP1cc repair in neuronal survival

Sporadic Alzheimer's and Parkinson's Disease

Beyond monogenic SCAN1, TDP1 dysfunction contributes to sporadic [Alzheimer's disease](/diseases/alzheimers-disease) and [Parkinson's disease](/diseases/parkinsons-disease)[@huang2018][@dean2015]:

Molecular Mechanisms

TDP1 in the DNA Damage Response Network

TDP1 interacts with multiple DNA repair pathways[@plo2015]:

Pathway Diagram

Therapeutic Perspectives

TDP1 as a Drug Target

TDP1 is simultaneously a therapeutic target for cancer and neuroprotection[@zhou2015][@liu2017]:

In Cancer:

• TDP1 inhibitors sensitize cancer cells to TOP1 inhibitors (camptothecins)
• Particularly relevant for tumors with high TOP1 expression or HR defects
• Active drug discovery programs for TDP1 inhibitors

• Enhancing TDP1 activity could protect neurons from TOP1cc accumulation
• Small molecule activators of TDP1 are being explored
• However, caution is needed: excessive TOP1 activity could promote genomic instability in neurons

Topoisomerase I Inhibitors and Neurotoxicity

Camptothecin derivatives (irinotecan, topotecan) are used as chemotherapy agents, but they cause neurotoxicity because they stabilize TOP1cc. In neurons, this is particularly damaging because:

• Neurons cannot dilute out the damage through cell division
• TDP1 becomes overwhelmed by the increased TOP1cc load
• The resulting transcriptional and replicative stress leads to neuronal death

See Also

• [DNA Repair in Neurodegeneration](/mechanisms/dna-repair-neurodegeneration) — TDP1 and TOP1cc repair
• [Parkinson's Disease](/diseases/parkinsons-disease) — dopaminergic neuron vulnerability
• [Alzheimer's Disease](/diseases/alzheimers-disease) — TDP1 connection
• [Mitochondrial DNA Repair](/mechanisms/mitochondrial-dna-repair) — mtDNA maintenance
• [Topoisomerase Inhibitors](/mechanisms/topoisomerase-inhibition) — TOP1cc mechanism

References