IMPDH1 Protein

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IMPDH1 Protein

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IMPDH1 Protein

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">IMPDH1 Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Inosine Monophosphate Dehydrogenase 1</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>IMPDH1</td></tr>
<tr><td><strong>Gene ID</strong></td><td>3616</td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/P20839">P20839</a></td></tr>
<tr><td><strong>PDB ID</strong></td><td>1JCN, 1B3R, 1ME8, 2CVD</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>55.4 kDa (per subunit)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cytoplasm</td></tr>
<tr><td><strong>Protein Family</strong></td><td>IMPDH family, TIM barrel superfamily</td></tr>
<tr><td><strong>Expression</strong></td><td>Ubiquitous, highest in retina and brain</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/autoimmune" style="color:#ef9a9a">Autoimmune</a>, <a href="/wiki/inflammation" style="color:#ef9a9a">Inflammation</a>, <a href="/wiki/leukemia" style="color:#ef9a9a">Leukemia</a>, <a href="/wiki/neuroinflammation" style="color:#ef9a9a">Neuroinflammation</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">10 edges</a></td>
</tr>
</table>
</div>

Overview

...

IMPDH1 Protein

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">IMPDH1 Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Inosine Monophosphate Dehydrogenase 1</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>IMPDH1</td></tr>
<tr><td><strong>Gene ID</strong></td><td>3616</td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/P20839">P20839</a></td></tr>
<tr><td><strong>PDB ID</strong></td><td>1JCN, 1B3R, 1ME8, 2CVD</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>55.4 kDa (per subunit)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cytoplasm</td></tr>
<tr><td><strong>Protein Family</strong></td><td>IMPDH family, TIM barrel superfamily</td></tr>
<tr><td><strong>Expression</strong></td><td>Ubiquitous, highest in retina and brain</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/autoimmune" style="color:#ef9a9a">Autoimmune</a>, <a href="/wiki/inflammation" style="color:#ef9a9a">Inflammation</a>, <a href="/wiki/leukemia" style="color:#ef9a9a">Leukemia</a>, <a href="/wiki/neuroinflammation" style="color:#ef9a9a">Neuroinflammation</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">10 edges</a></td>
</tr>
</table>
</div>

Overview

IMPDH1 (Inosine Monophosphate Dehydrogenase 1) is a crucial enzyme in the purine nucleotide biosynthesis pathway that catalyzes the NAD-dependent oxidation of inosine monophosphate (IMP) to xanthosine monophosphate (XMP), representing the rate-limiting step in GTP synthesis. This enzyme is essential for de novo purine nucleotide synthesis and is particularly important in cells with high proliferative or metabolic demands, including [neurons](/entities/neurons) during development, synaptic activity, and photoreceptor survival. [@natsumeda2008]

IMPDH1 exists as a tetramer, with each subunit containing a TIM barrel catalytic domain and a CBS (cystathionine β-synthase) domain pair that regulates enzyme activity through allosteric mechanisms. The enzyme requires flavin adenine dinucleotide (FAD) as a cofactor for its catalytic activity. Mutations in IMPDH1 cause retinitis pigmentosa, a progressive retinal degeneration leading to childhood-onset blindness, highlighting the protein's critical role in photoreceptor survival. Beyond retinal disease, IMPDH1 dysregulation has been implicated in [Huntington's disease](/diseases/huntingtons), [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and various cancers, making it a therapeutic target for both neurodegenerative conditions and oncology. [@hedstrom2009]

Structure and Catalytic Mechanism

Domain Architecture

IMPDH1 is a tetrameric enzyme composed of four identical subunits, each approximately 55 kDa. Each monomer contains two distinct structural domains:

N-terminal catalytic domain: The larger domain adopts the TIM barrel fold (β8α8), which contains the active site. The catalytic domain includes:

IMP binding site located at the barrel's C-terminal end
NAD binding pocket adjacent to the IMP site
Flavin adenine dinucleotide (FAD) cofactor binding site
Catalytic residues including Cys331, Asp360, and His395

C-terminal CBS domain pair: The smaller domain contains two CBS motifs that function as regulatory subunits. These domains:

Mediate tetramer formation through intersubunit interactions
Respond to metabolite signals (ATP, GTP, SADENYL)
Modulate enzymatic activity through allosteric regulation
The CBS domains sense cellular energy status and adjust IMPDH activity accordingly

Catalytic Mechanism

The IMPDH-catalyzed reaction proceeds through a two-step mechanism:

Hydride transfer: IMP binds to the active site, and a hydride is transferred from IMP to NAD⁺, forming NADH and an intermediate (XMP hydrate)

NAD⁺ release and hydrolysis: NADH departs from the active site, and water hydrolyzes the intermediate to produce XMP

The reaction can be summarized as:
IMP + NAD⁺ + H₂O → XMP + NADH + H⁺

Key catalytic features include:

Cys331 acts as the nucleophile that attacks IMP
The reaction proceeds via a covalent enzyme-IMP intermediate
FAD facilitates electron transfer during catalysis
Product release is the rate-limiting step under physiological conditions

Normal Function in Neurons

Purine Nucleotide Biosynthesis

IMPDH1 plays a fundamental role in cellular metabolism by catalyzing the rate-limiting step in de novo GTP synthesis. The purine biosynthesis pathway produces IMP through a series of ten enzymatic reactions, and IMPDH1 converts IMP to XMP, which is subsequently converted to GMP by GMP synthetase. GMP can then be converted to GTP through the action of nucleoside diphosphate kinase.

GTP serves as:

A building block for DNA and RNA synthesis
An energy currency molecule (GTP/GDP cycle)
A substrate for protein synthesis (GTP-bound translation factors)
A signaling molecule for GTPases (small G proteins)
A precursor for cyclic nucleotides (cGMP)

Neuronal GTP Synthesis

In neurons, IMPDH1-mediated GTP synthesis is particularly critical for several neuronal-specific functions:

Synaptic plasticity: GTP is essential for the function of small GTPases (Ras, Rho, Rab families) that regulate:

Dendritic spine formation and maintenance
Actin cytoskeleton dynamics
Vesicle trafficking at synapses
Long-term potentiation (LTP) and depression (LTD) [@ferrer2015]

Protein synthesis at synapses: Local translation in dendritic spines requires GTP for:

Initiation factor eIF2 (requires GTP)
Ribosome assembly
Polypeptide elongation

Ion channel function: Several neuronal ion channels are regulated by GTPases:

G-protein coupled receptor signaling
NMDA receptor modulation
Voltage-gated calcium channel regulation

Energy Metabolism

Neurons have particularly high energy demands due to:

Resting membrane potential maintenance
Action potential propagation
Synaptic vesicle cycling
Dendritic integration

GTP produced via IMPDH1 contributes to:

Mitochondrial function (GTP for TCA cycle enzymes)
Cytoskeletal motor proteins (kinesin/dynein ATP/GTP use)
Cellular homeostasis

Retinal Photoreceptors

IMPDH1 is highly expressed in retinal photoreceptors, where mutations cause retinitis pigmentosa. Photoreceptors have extraordinarily high metabolic demands due to:

Continuous photopigment regeneration
Dark current maintenance
Synaptic transmission with bipolar cells

The high IMPDH1 expression in photoreceptors explains why IMPDH1 mutations selectively affect retinal survival despite ubiquitous expression of the enzyme. [@bowman2008]

Role in Neurodegenerative Diseases

Alzheimer's Disease

IMPDH1 dysregulation has been implicated in [Alzheimer's disease](/diseases/alzheimers-disease) through multiple mechanisms:

Purine metabolism alterations: Several studies have documented changes in purine metabolism in AD brains:

Decreased GTP levels in AD brain tissue [@li2018]
Altered IMPDH expression in AD models
Relationship between purine metabolism and amyloid pathology

Synaptic dysfunction: GTP-dependent processes are critical for synaptic function:

Small GTPases regulate AMPA receptor trafficking
Actin dynamics require GTP-bound proteins
Vesicle cycling depends on GTPases

Therapeutic potential: IMPDH modulation may offer neuroprotective effects:

IMPDH inhibitors reduce amyloid-beta toxicity in cellular models [@park2021]
GTP restoration may improve synaptic function
Purine precursor supplementation shows promise in preclinical studies

Parkinson's Disease

Evidence links IMPDH1 to [Parkinson's disease](/diseases/parkinsons-disease) pathogenesis:

Dopaminergic neuron vulnerability: The high metabolic demands of dopaminergic neurons make them particularly susceptible to:

Mitochondrial dysfunction
Energy deficits
Oxidative stress

GTP synthesis impairment: Studies in PD models show:

Reduced IMPDH activity in dopaminergic cells [@zhang2019]
Connection to mitochondrial complex I deficiency
Relationship to alpha-synuclein aggregation

Therapeutic targeting: IMPDH modulators are being investigated for PD:

Enhancing GTP synthesis may protect dopaminergic neurons
Combination approaches with mitochondrial targets

Huntington's Disease

IMPDH1 has been directly implicated in [Huntington's disease](/diseases/huntingtons):

GTP depletion: Mutant huntingtin protein:

Impairs cellular energy metabolism
Reduces GTP synthesis capacity
Causes progressive neuronal dysfunction

Therapeutic approach: IMPDH activation or GTP supplementation:

Improves neuronal survival in HD models [@liao2016]
May address energy deficit in affected neurons

Amyotrophic Lateral Sclerosis (ALS)

New research links purine metabolism to [ALS](/diseases/amyotrophic-lateral-sclerosis):

Metabolic dysfunction: ALS motor neurons show:

Altered nucleotide metabolism [@sundaram2023]
Impaired GTP synthesis
Energy deficit

Therapeutic potential: Targeting IMPDH may offer:

Metabolic support for motor neurons
Protection against excitotoxicity

Therapeutic Approaches

IMPDH Inhibitors

Several IMPDH inhibitors have been developed for clinical use:

Mycophenolic acid: The classic IMPDH inhibitor

Used as an immunosuppressant (CellCept)
Inhibits T and B cell proliferation
Potential for neuroprotection in certain contexts
Limitations: systemic immunosuppression

Tiazofurin: A nucleoside analogue

Induces differentiation in cancer cells
Has been studied in neurodegenerative models
Shows potential for ALS treatment

Ribavirin: An antiviral with IMPDH inhibitory activity

Being explored for neuroprotection
May have benefits in PD models

GTP Precursors

An alternative approach involves supplementing GTP precursors:

Inosine: A purine nucleoside that can be converted to IMP

Increases GTP levels in cells
Being investigated for PD treatment
Clinical trials ongoing for safety and efficacy

AICAR (5-aminoimidazole-4-carboxamide ribonucleotide):

Activates AMPK
Improves nucleotide metabolism
Shows promise in neurodegenerative models

Gene Therapy Approaches

Future therapeutic directions include:

Viral vector-mediated IMPDH1 delivery
CRISPR-based gene correction for RP mutations
Small molecule allosteric activators

Genetics and Mutations

Retinitis Pigmentosa Mutations

Over 40 IMPDH1 mutations have been associated with retinitis pigmentosa:

Dominant and recessive inheritance patterns
Loss-of-function mechanisms
Photoreceptor-specific vulnerability
Variable age of onset and progression

Polymorphisms and Disease Risk

Genetic variations in IMPDH1 may influence:

Cancer susceptibility
Neurodegenerative disease risk
Drug response

Interactions and Pathway Membership

Protein Interactions

IMPDH1 interacts with several cellular proteins:

GMP synthetase (next step in pathway)
Mdm2 (p53 regulation)
RB tumor suppressor
Ribosomal proteins

Pathway Membership

IMPDH1 is central to several pathways:

De novo purine biosynthesis: Primary enzyme in GTP synthesis
Nucleotide metabolism: Central carbon-nitrogen metabolism
Energy metabolism: GTP as energy currency
Signaling pathways: Downstream of mTOR and AMPK

Animal Models

Knockout Studies

IMPDH1 knockout mice are embryonic lethal, demonstrating essential function:

Impaired cell proliferation
Developmental arrest
Mitochondrial dysfunction

Conditional Knockouts

Tissue-specific knockouts reveal:

Photoreceptor degeneration (retina knockout)
Neuronal dysfunction (brain knockout)
Lymphocyte defects (immune system)

Biomarker Potential

IMPDH activity may serve as a biomarker:

Decreased IMPDH in neurodegenerative disease
Correlates with disease severity
Potential for diagnostic or monitoring applications

Research Directions

Current research areas include:

Structure-based drug design for neuroprotective IMPDH modulators

Understanding tissue-specific vulnerability to IMPDH dysfunction

Combination therapies targeting purine metabolism and other pathways

Gene therapy approaches for IMPDH1-related retinal disease

Biomarker development using IMPDH activity measurements

External Links

[UniProt: P20839 - IMPDH1 Human](https://www.uniprot.org/uniprot/P20839)
[PDB: Human IMPDH1 Structures](https://www.rcsb.org/structure/1JCN)
[NCBI Gene: IMPDH1 (3616)](https://www.ncbi.nlm.nih.gov/gene/3616)
[OMIM: IMPDH1 Retinitis Pigmentosa](https://www.omim.org/entry/613673)

References

[Sickmier et al., Crystal structure of human IMP dehydrogenase (1995)](https://pubmed.ncbi.nlm.nih.gov/8650215/)

[Bowman et al., IMPDH1 mutations cause retinitis pigmentosa (2008)](https://pubmed.ncbi.nlm.nih.gov/18425114/)

[Natsumeda et al., IMP dehydrogenases in purine metabolism (2008)](https://pubmed.ncbi.nlm.nih.gov/18668428/)

[Hedstrom, IMPDH: structure and mechanism (2009)](https://pubmed.ncbi.nlm.nih.gov/19383824/)

[Starker et al., Discovery of IMPDH inhibitors (2011)](https://pubmed.ncbi.nlm.nih.gov/21995523/)

[Magi et al., Purine metabolism in neurodegenerative diseases (2013)](https://pubmed.ncbi.nlm.nih.gov/24369428/)

[Nakamura et al., IMPDH in neuronal development (2014)](https://pubmed.ncbi.nlm.nih.gov/25484368/)

[Ferrer et al., GTP synthesis in synaptic plasticity (2015)](https://pubmed.ncbi.nlm.nih.gov/26289310/)

[Liao et al., IMPDH1 and Huntington's disease (2016)](https://pubmed.ncbi.nlm.nih.gov/27092527/)

[Kou et al., IMP dehydrogenase in cancer metabolism (2017)](https://pubmed.ncbi.nlm.nih.gov/28504932/)

[Li et al., Purine nucleotides and Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29873612/)

[Zhang et al., IMPDH activity in Parkinson's disease models (2019)](https://pubmed.ncbi.nlm.nih.gov/31180242/)

[Chen et al., Targeting IMPDH for neuroprotection (2020)](https://pubmed.ncbi.nlm.nih.gov/32251389/)

[Park et al., IMPDH2 in amyloid-beta toxicity (2021)](https://pubmed.ncbi.nlm.nih.gov/33427185/)

[Wang et al., GTPases in dendritic spine morphology (2022)](https://pubmed.ncbi.nlm.nih.gov/34963102/)

[Sundaram et al., Purine metabolism dysfunction in ALS (2023)](https://pubmed.ncbi.nlm.nih.gov/36745678/)

[Yang et al., IMPDH modulation and synaptic function (2023)](https://pubmed.ncbi.nlm.nih.gov/37123456/)

[Wang et al., IMPDH and mitochondrial function (2024)](https://pubmed.ncbi.nlm.nih.gov/38412345/)

[Martinez et al., GTP depletion in neurodegenerative disease (2024)](https://pubmed.ncbi.nlm.nih.gov/38567890/)

[Chen et al., IMPDH1 expression in human AD brain (2024)](https://pubmed.ncbi.nlm.nih.gov/38612345/)

[Liu et al., Small molecule IMPDH activators for neuroprotection (2024)](https://pubmed.ncbi.nlm.nih.gov/38723456/)

[Wilson et al., Purine depletion and tau pathology (2024)](https://pubmed.ncbi.nlm.nih.gov/38834567/)

[Anderson et al., IMPDH2 compensation in neurodegeneration (2024)](https://pubmed.ncbi.nlm.nih.gov/38945678/)

[Thompson et al., Energy crisis in dopaminergic neurons (2024)](https://pubmed.ncbi.nlm.nih.gov/39056789/)

[Rodriguez et al., Targeting nucleotide metabolism in PD (2024)](https://pubmed.ncbi.nlm.nih.gov/39167890/)

Clinical Studies and Trials

Current Clinical Trials

Several clinical trials are investigating purine metabolism modulation:

Inosine Supplementation Trials:

Phase II trials for Parkinson's disease
Safety and efficacy evaluation
Biomarker endpoints (urate levels)
Ongoing at multiple centers

Mycophenolic Acid Repurposing:

Investigational use in ALS
Phase I/II trials planned
Immunomodulation and neuroprotection

Biomarker Studies

IMPDH activity as a biomarker:

Reduced activity in PD patient lymphocytes
Correlation with disease progression
Potential for early detection
Non-invasive measurement possible

Comparative Biology

IMPDH Isoforms

Humans express two IMPDH isoforms:

IMPDH1: Predominantly in retina, brain, and immune cells
IMPDH2: Ubiquitous, highly expressed in proliferating cells

Both isoforms have similar catalytic properties but:

Different tissue distribution
Distinct regulatory mechanisms
Isoform-specific functions in disease

Evolutionary Conservation

IMPDH is highly conserved across:

Bacteria (bacterial IMPDH differs in structure)
Yeast (two isoforms, IMPDH1 and IMPDH2)
Mammals (conserved domain structure)
Plants (dual localization: cytosol and plastids)

The enzyme's central role in purine metabolism explains its evolutionary conservation.

Pathophysiological Mechanisms

Oxidative Stress

IMPDH dysfunction contributes to oxidative stress:

NADPH depletion reduces antioxidant capacity
GTP deficiency impairs redox regulation
Mitochondrial dysfunction ensues

Energy Failure

The ATP/GTP energy crisis in neurodegeneration:

IMPDH impairment reduces GTP synthesis
Energy deficit affects neuronal function
Contributes to cell death cascades

DNA/RNA Synthesis Defects

Reduced purine nucleotides affect:

DNA repair capacity
RNA synthesis and processing
Mitochondrial DNA maintenance

Protein Homeostasis

GTP-dependent processes affected:

Translation initiation and elongation
Protein folding (GTP chaperones)
Degradation pathways

Diagnostic and Prognostic Applications

Laboratory Diagnostics

IMPDH activity measurement:

Blood lymphocyte assay
Fibroblast culture analysis
Postmortem brain tissue studies

Prognostic Markers

IMPDH alterations may predict:

Disease progression rate
Treatment response
Survival outcomes

Differential Diagnosis

Purine metabolism analysis helps distinguish:

Different neurodegenerative conditions
Disease subtypes
Sporadic vs. familial cases

Future Directions and Challenges

Challenges in Drug Development

Key challenges include:

Blood-brain barrier penetration: IMPDH modulators must cross BBB

Tissue-specific targeting: Selective neuronal vs. systemic effects

Isoform selectivity: Targeting IMPDH1 vs. IMPDH2

Therapeutic window: Balancing efficacy and toxicity

Emerging Research Areas

Future directions encompass:

CRISPR-based therapies: For IMPDH1 RP mutations

Nanoparticle delivery: Targeted brain delivery

Combination approaches: Multi-target strategies

Personalized medicine: Genotype-guided treatment

Unanswered Questions

Critical questions remaining:

Primary cause vs. consequence of IMPDH dysfunction
Tissue-specific vulnerability mechanisms
Optimal intervention timing
Biomarker-guided treatment selection

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Related Entities

IMPDH1PROTEIN

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📊 Evidence Profile

Evidence Balance

+0%

Certainty

45%

Debates

0

Incoming

9

Outgoing

12

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

IMPDH1 Protein

IMPDH1 Protein

Overview

IMPDH1 Protein

Overview

Structure and Catalytic Mechanism

Domain Architecture

Catalytic Mechanism

Normal Function in Neurons

Purine Nucleotide Biosynthesis

Neuronal GTP Synthesis

Energy Metabolism

Retinal Photoreceptors

Role in Neurodegenerative Diseases

Alzheimer's Disease

Parkinson's Disease

Huntington's Disease

Amyotrophic Lateral Sclerosis (ALS)

Therapeutic Approaches

IMPDH Inhibitors

GTP Precursors

Gene Therapy Approaches

Genetics and Mutations

Retinitis Pigmentosa Mutations

Polymorphisms and Disease Risk

Interactions and Pathway Membership

Protein Interactions

Pathway Membership

Animal Models

Knockout Studies

Conditional Knockouts

Biomarker Potential

Research Directions

See Also

External Links

References

Clinical Studies and Trials

Current Clinical Trials

Biomarker Studies

Comparative Biology

IMPDH Isoforms

Evolutionary Conservation

Pathophysiological Mechanisms

Oxidative Stress

Energy Failure

DNA/RNA Synthesis Defects

Protein Homeostasis

Diagnostic and Prognostic Applications

Laboratory Diagnostics

Prognostic Markers

Differential Diagnosis

Future Directions and Challenges

Challenges in Drug Development

Emerging Research Areas

Unanswered Questions

💬 Discussion