IMPDH2 Protein

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IMPDH2 Protein

Introduction

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">IMPDH2 Protein</th>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>IMPDH2</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Inosine Monophosphate Dehydrogenase 2</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>P12282</td>
</tr>
<tr>
<td class="label">PDB Structures</td>
<td>1ME7, 1B8O, 3L1N</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>55,640 Da</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Cytoplasm, Nucleus</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>IMPDH family</td>
</tr>
<tr>
<td class="label">Drug</td>
<td>Mechanism</td>
</tr>
<tr>
<td class="label">Mycophenolate mofetil</td>
<td>Non-competitive inhibition</td>
</tr>
<tr>
<td class="label">Ribavirin</td>
<td>NAD+ analog</td>
</tr>
<tr>
<td class="label">Tiazofurin</td>
<td>Competitive inhibition</td>
</tr>
<tr>
<td class="label">Mizoribine</td>
<td>Competitive inhibition</td>
</tr>
</table>

IMPDH2 (Inosine Monophosphate Dehydrogenase 2) is a rate-limiting enzyme in de novo purine nucleotide synthesis. It catalyzes the NAD-dependent oxidation of IMP to XMP, the committed step in GTP biosynthesis. IMPDH2 is essential for proliferating cells, including immune cells and neurons under stress [@brown2000].

...

IMPDH2 Protein

Introduction

The protein forms tetramers and is a key target for immunosuppressant and antiviral drugs. Recent research links IMPDH2 dysregulation to several neurodegenerative disorders, including [Alzheimer disease](/diseases/alzheimers-disease), [Parkinson disease](/diseases/parkinsons-disease), and retinitis pigmentosa.

Overview

IMPDH2 is a 514-amino acid enzyme that catalyzes the rate-limiting step in GTP synthesis. The enzyme is essential for cell proliferation and is particularly important in cells with high metabolic demand, including [neurons](/entities/neurons), immune cells, and photoreceptor cells.

Dysregulation of IMPDH2 contributes to neurodegenerative diseases through impaired purine metabolism, leading to nucleotide depletion and altered GTP-dependent signaling [@stolte2020].

Basic Information

Structure and Function

Molecular Architecture

IMPDH2 forms a tetrameric enzyme complex (approximately 220 kDa). Each monomer contains:

Catalytic core domain: Binds IMP and NAD+

CBS regulatory domains: Two CBS domains for allosteric regulation

Active site: Where IMP oxidation occurs

The enzyme undergoes conformational changes during catalysis, transitioning between active and inactive states based on GTP levels [@hedstrom2009].

Catalytic Mechanism

IMPDH2 catalyzes the two-step oxidation of IMP to XMP:

IMP + NAD+ → XMP + NADH (rate-limiting step)

XMP + ATP → AMP + ADP (via GMP synthetase)

Tissue Distribution

Brain: Moderate expression in cortex, hippocampus
Retina: High expression in photoreceptors
Immune system: High expression in proliferating immune cells
Cellular localization: Cytoplasm

Role in Neurodegeneration

Retinitis Pigmentosa

IMPDH1/2 mutations cause autosomal dominant retinitis pigmentosa. Photoreceptor cells are particularly vulnerable to nucleotide imbalance due to their high metabolic demand for phototransduction [@bowne2002].

Mechanism: Mutant IMPDH forms abnormal tetramers
Phenotype: Progressive photoreceptor degeneration
Onset: Adolescence to early adulthood

Alzheimer Disease

Impaired purine metabolism is increasingly recognized in [Alzheimer disease](/diseases/alzheimers-disease). Studies show altered IMPDH activity in AD brains, correlating with neurofibrillary tangle formation [@pietzsch2022]:

GTP depletion: Affects tau phosphorylation through altered kinase activity
Nucleotide imbalance: Impairs DNA repair
Energy failure: Reduced GTP for mitochondrial function

Parkinson Disease

In [Parkinson disease](/diseases/parkinsons-disease), IMPDH dysregulation affects dopaminergic neurons:

6-OHDA models: Show IMPDH inhibition
Nucleotide depletion: Contributes to neuronal vulnerability
NAD+ metabolism: Linked to sirtuin activity

ALS and Motor Neuron Disease

Altered purine metabolism in motor neurons:

IMPDH2 expression: Changes in ALS models
Ribavirin trials: Tested in ALS (Phase 2 showed some benefit) [@siddle2018]
Mycophenolate: Tested but not beneficial in Phase 3

Therapeutic Targeting

IMPDH Inhibitors

Several IMPDH inhibitors have been developed:

Clinical Trials in Neurodegeneration

Ribavirin in ALS: Phase 2 trials showed some benefit but was discontinued [@siddle2018]
Mycophenolate in ALS: Phase 3 showed no benefit
Gene therapy: AAV-IMPDH for retinitis pigmentosa under development

Molecular Pathways

Mermaid diagram (expand to render)

Research Gaps and Future Directions

Brain-penetrant inhibitors: Need for IMPDH modulators that cross the blood-brain barrier

Biomarkers: Purine metabolism markers for patient stratification

Gene therapy: AAV-delivered IMPDH for retinitis pigmentosa

Combination approaches: Targeting both purine synthesis and downstream pathways

Cross-References

[IMPDH2 Gene](/genes/impdh2) - Gene page
[Purine Metabolism](/mechanisms/purine-metabolism) - Related pathway
[Retinitis Pigmentosa](/diseases/retinitis-pigmentosa) - Associated disease
[Alzheimer Disease](/diseases/alzheimers-disease) - Related disease
[Parkinson Disease](/diseases/parkinsons-disease) - Related disease
[GTPase Signaling](/mechanisms/gtpase-signaling) - Downstream pathway
[Tau Protein](/proteins/tau) - GTP-dependent phosphorylation

Key Publications

[Brown K, et al. (2000). Structure of human IMP dehydrogenase](https://pubmed.ncbi.nlm.nih.gov/10700255/)

[Hedstrom L (2009). IMP dehydrogenase structure, function, and inhibition](https://pubmed.ncbi.nlm.nih.gov/19149576/)

[Stolte B, et al. (2020). IMPDH mutations cause retinal degeneration](https://pubmed.ncbi.nlm.nih.gov/32840789/)

[Bowne S, et al. (2002). Mutations in IMPDH1 cause autosomal dominant retinitis pigmentosa](https://pubmed.ncbi.nlm.nih.gov/12417540/)

[Siddle H, et al. (2018). Ribavirin treatment in ALS Phase 2 trial](https://pubmed.ncbi.nlm.nih.gov/29330324/)

External Links

[UniProt](https://www.uniprot.org/uniprot/P12282) - Protein database
[PDB](https://www.rcsb.org/) - Structural data
[PubMed](https://pubmed.ncbi.nlm.nih.gov/?term=IMPDH2+neurodegeneration) - Literature
[KEGG Pathways](https://www.genome.jp/kegg/pathway.html) - Pathway database

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