GLUL — Glutamine Synthetase

GLUL — Glutamine Synthetase

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">GLUL — Glutamine Synthetase</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>GLUL</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Glutamate-Ammonia Ligase (Glutamine Synthetase)</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>1q31.3</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/2785" target="_blank">2785</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000135821" target="_blank">ENSG00000135821</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/610012" target="_blank">610012</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P15104" target="_blank">P15104</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>[Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), [ALS](/diseases/als), Epilepsy</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Astrocytes (highest), Oligodendrocytes, Neurons (low)</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Variants</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">p.R324C, p.E286K, Promoter variants</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f

GLUL — Glutamine Synthetase

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">GLUL — Glutamine Synthetase</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>GLUL</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Glutamate-Ammonia Ligase (Glutamine Synthetase)</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>1q31.3</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/2785" target="_blank">2785</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000135821" target="_blank">ENSG00000135821</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/610012" target="_blank">610012</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P15104" target="_blank">P15104</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>[Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), [ALS](/diseases/als), Epilepsy</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Astrocytes (highest), Oligodendrocytes, Neurons (low)</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Variants</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">p.R324C, p.E286K, Promoter variants</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">7 edges</a></td>
</tr>
</table>

GLUL — Glutamine Synthetase

Overview

The GLUL gene encodes glutamine synthetase (GS), also known as glutamate-ammonia ligase, a central enzyme in nitrogen metabolism that catalyzes the ATP-dependent synthesis of glutamine from glutamate and ammonia. In the brain, glutamine synthetase is predominantly expressed in [astrocytes](/cell-types/astrocytes) and plays essential roles in glutamate homeostasis, neurotransmitter recycling (the glutamine-glutamate cycle), ammonia detoxification, and protection against excitotoxicity ([Norenberg et al., 2010](https://pubmed.ncbi.nlm.nih.gov/21059219/)).

Glutamine synthetase is a 392-amino acid enzyme that forms decameric complexes (10 subunits) in the cytosol. It is a key astroglial marker and is critically implicated in various [neurodegenerative diseases](/diseases/alzheimers-disease), including [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and [amyotrophic lateral sclerosis (ALS)](/diseases/als), as well as in epilepsy and multiple sclerosis ([Martinez et al., 2019](https://pubmed.ncbi.nlm.nih.gov/30506178/)). The gene is catalogued as NCBI Gene ID [2785](https://www.ncbi.nlm.nih.gov/gene/2785) and OMIM [610012](https://omim.org/entry/610012).

Gene Structure and Protein Domain Architecture

Genomic Organization

The GLUL gene spans approximately 17.4 kb on chromosome 1q31.3 (position 182,375,451-182,392,885 on the forward strand). The gene consists of 12 coding exons that encode the 392-amino acid glutamine synthetase protein with a molecular weight of approximately 42 kDa per subunit. The enzyme forms homodecamers (10 subunits) with a total molecular weight of approximately 420 kDa.

Protein Domain Structure

Glutamine synthetase contains several functionally important regions:

• N-terminal Domain (aa 1-100): Contains the active site for glutamine synthesis
• C-terminal Domain (aa 250-350): Involved in subunit interactions and assembly
• ATP-Binding Site: Catalyzes ATP-dependent amino acid activation
• Glutamate-Binding Pocket: Recognizes glutamate substrate
• Ammonia Channel: Facilitates ammonia access to the active site
• Inter-subunit Contact Sites: Critical for decamer formation

• ATP: Energy donor for the reaction
• Mg²⁺ or Mn²⁺: Essential metal ion cofactors
• Glutamate: Amino acid substrate
• Ammonia: Nitrogen donor

Normal Biological Functions

Enzymatic Activity and Reaction

Glutamine synthetase catalyzes the following reaction:

Glutamate + NH₃ + ATP → Glutamine + ADP + Pi

The reaction occurs in two half-reactions:

This reaction is essential for:

• Nitrogen metabolism and detoxification
• Amino acid biosynthesis
• pH regulation

Glutamate Homeostasis and the Glutamine-Glutamate Cycle

One of the most critical functions of GS in the brain is its role in maintaining glutamate homeostasis ([Schousboe et al., 2019](https://pubmed.ncbi.nlm.nih.gov/30604225/)):

This cycle, known as the glutamine-glutamate cycle or GABA-glutamate cycle, is essential for:

• Maintaining synaptic glutamate levels
• Preventing excitotoxic glutamate accumulation
• Providing metabolic support to neurons

Ammonia Detoxification

GS plays a critical role in brain ammonia detoxification ([Albrecht et al., 2019](https://pubmed.ncbi.nlm.nih.gov/30968334/)):

• Ammonia Scavenging: GS traps toxic ammonia in the form of glutamine
• Prevention of Hepatic Encephalopathy: Reduced GS activity contributes to hepatic encephalopathy
• Blood-Brain Barrier Protection: Prevents ammonia-induced cerebral edema
• pH Regulation: Glutamine synthesis helps regulate intracellular pH

Astrocytic Functions

GS is predominantly expressed in astrocytes and supports their functions:

• Astrocytic Identity: GS is a classic astrocytic marker
• Potassium Buffering: Supports astrocytic K⁺ homeostasis
• Water Balance: Contributes to astrocytic volume regulation
• Metabolic Support: Provides glutamine for neuronal metabolism

Neuroprotection

GS provides neuroprotection through multiple mechanisms:

• Excitotoxicity Prevention: Removes extracellular glutamate
• Oxidative Stress Reduction: Glutamine is a precursor for glutathione synthesis
• Osmotic Regulation: Helps maintain osmotic balance
• Blood-Brain Barrier Support: Protects BBB function

Role in Neurodegenerative Diseases

Alzheimer's Disease

Glutamine synthetase is significantly downregulated in [Alzheimer's disease](/diseases/alzheimers-disease) brain ([Su et al., 2021](https://pubmed.ncbi.nlm.nih.gov/34092254/)):

• Reduced GS Expression: 40-60% reduction in AD brain
• Mechanisms: Amyloid-beta toxicity, tau pathology, neuroinflammation
• Consequences: Impaired glutamate recycling, excitotoxicity
• Therapeutic Target: GS activators being explored

Parkinson's Disease

GS dysfunction contributes to [Parkinson's disease](/diseases/parkinsons-disease) pathogenesis ([Yang et al., 2022](https://pubmed.ncbi.nlm.nih.gov/35054178/)):

• Astrocytic GS Deficiency: Reduced astrocytic GS in PDsubstantia nigra
• Excitotoxicity: Contributes to dopaminergic neuron vulnerability
• Metabolic Dysfunction: Alters glutamine-glutamate cycle
• Therapeutic Potential: AAV-GS delivery being investigated

Amyotrophic Lateral Sclerosis

GS abnormalities are found in [ALS](/diseases/als) ([Ortiz et al., 2021](https://pubmed.ncbi.nlm.nih.gov/33813157/)):

• Motor Neuron Vulnerability: GS deficiency increases excitotoxicity
• Astrocytic Dysfunction: Loss of astrocytic GS support
• Glutamate Transport: GS interacts with EAAT2 (GLT-1)
• Therapeutic Target: Enhancing GS activity

Epilepsy

GS plays a complex role in [epilepsy](/diseases/epilepsy) ([Müller et al., 2020](https://pubmed.ncbi.nlm.nih.gov/31903623/)):

• Reduced GS in Hippocampus: Associated with seizure susceptibility
• Excitotoxicity: Contributes to seizure-induced neuronal damage
• Therapeutic Potential: GS modulators for seizure control
• Astrocytic Dysfunction: GS loss in epileptic tissue

Multiple Sclerosis

GS involvement in [multiple sclerosis](/diseases/multiple-sclerosis) ([Peterson et al., 2020](https://pubmed.ncbi.nlm.nih.gov/32239687/)):

• Demyelination Effects: Loss of oligodendrocyte support
• Astrocytic Response: Reactive astrocytes upregulate GS
• Neuroprotection: GS supports axon survival

Molecular Mechanisms

Excitotoxicity and Glutamate Homeostasis

The primary mechanism by which GS deficiency contributes to neurodegeneration is through excitotoxicity:

Ammonia Toxicity

When GS is deficient, ammonia accumulates to toxic levels:

• Neurotoxicity: Ammonia directly damages neurons
• Brain Edema: Causes cerebral swelling
• Cognitive Impairment: Contributes to hepatic encephalopathy
• Seizures: Lowers seizure threshold

Astrocyte-Neuron Metabolic Coupling

GS supports astrocyte-neuron metabolic coupling ([Kim et al., 2023](https://pubmed.ncbi.nlm.nih.gov/37088921/)):

• Lactate Shuttle: Astrocytic glycogen metabolism supports neurons
• Glutamine Supply: Provides neurotransmitter precursors
• Oxidative Stress Defense: Supports glutathione synthesis
• Ion Homeostasis: Helps maintain ionic balance

Therapeutic Approaches

Small Molecule Activators

Compounds that enhance GS activity are being developed:

• GS Stabilizers: Prevent protein degradation
• Transcription Enhancers: Increase GS expression
• Substrate Analogs: Improve catalytic efficiency
• Astrocyte-Targeted Drugs: Enhance astrocytic function

Gene Therapy

Viral delivery approaches to restore GS:

• AAV-GLUL: Adeno-associated virus-mediated GS expression
• Astrocyte-Specific Promoters: Targeted expression
• Combination Approaches: GS with other therapeutic genes

Metabolic Modulation

Supporting glutamine metabolism:

• Glutamine Supplementation: Precursor for glutamine synthesis
• Glutamate Transporters: Enhance EAAT1/2 function
• Antioxidants: Support glutathione synthesis

Repurposed Drugs

FDA-approved drugs with GS-modulating activity:

• L-DOPA: May affect glutamine metabolism
• Riluzole: Modulates glutamate signaling
• Ceftriaxone: Upregulates glutamate transporters

Genetics and Population Studies

Disease-Associated Variants

| Variant | Effect | Clinical Significance |
|---------|--------|---------------------|
| p.R324C | Missense, reduced activity | Associated with neurodegeneration |
| p.E286K | Missense, impaired assembly | Found in ALS patients |
| Promoter variants | Altered expression | May modify disease risk |
| Deletions | Complete loss | Congenital glutamine deficiency |

Congenital Glutamine Deficiency

Rare autosomal recessive mutations in GLUL cause congenital glutamine deficiency ([Chen et al., 2023](https://pubmed.ncbi.nlm.nih.gov/36378541/)):

• Clinical Features: Microcephaly, seizures, developmental delay
• Mechanism: Complete loss of GS function
• Treatment: Glutamine supplementation (controversial)

Population Genetics

• Carrier Frequency: Rare in population databases
• Selection Pressure: Pathogenic variants under negative selection
• Ethnic Variation: Mutation spectrum differs by ancestry

Animal Models

Mouse Models

• Astrocyte-Specific Knockout: Shows neurodegeneration and seizures
• Conditional Deletion: Targeted to specific brain regions
• Transgenic Overexpression: Protective in some models
• Humanized Mice: Expressing human GLUL variants

Zebrafish Models

• Morphants: Show developmental abnormalities
• Knockouts: Reveal role in ammonia homeostasis

Diagnosis and Testing

Genetic Testing

Clinical testing for GLUL variants:

• NGS Panels: Neurodegeneration gene panels
• Whole Exome Sequencing: For atypical presentations
• Targeted Sequencing: For family members

Biomarkers

Research biomarkers in development:

• CSF Glutamine: Elevated in GS deficiency
• GS Activity: Peripheral blood mononuclear cells
• Astrocytic Markers: GFAP, S100β

Research Directions

Key questions remaining:

Key Publications

Pathway & Interaction Diagram

Interactive diagram showing GLUL's key relationships in the SciDEX knowledge graph (7 connections shown).

See Also

• [Genes Index](/genes)
• [Proteins Index](/proteins)
• [Diseases Index](/diseases)
• [Astrocytes](/cell-types/astrocytes) — Astrocytic cell type
• [Alzheimer's Disease](/diseases/alzheimers-disease) — Alzheimer's Disease
• [Parkinson's Disease](/diseases/parkinsons-disease) — Parkinson's Disease
• [Amyotrophic Lateral Sclerosis (ALS) — Diseases](/diseases/als)
• [Glutamate Signaling](/mechanisms/glutamate-signaling) — Glutamate neurotransmission
• [Excitotoxicity](/mechanisms/excitotoxicity) — Glutamate toxicity mechanisms
• [Astrocyte Function](/mechanisms/astrocyte-function) — Astrocytic biology

External Links

• [NCBI Gene: GLUL](https://www.ncbi.nlm.nih.gov/gene/2785)
• [Ensembl: GLUL](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000135821)
• [UniProt: P15104](https://www.uniprot.org/uniprot/P15104)
• [OMIM: 610012](https://omim.org/entry/610012)
• [Allen Brain Atlas: GLUL expression](https://human.brain-map.org/microarray/search/show?search_term=GLUL)

GLUL Gene

Introduction

Glul Gene Glutamine Synthetase 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-gene"> [@albrecht2019]

| Attribute | Value | [@su2021]
|-----------|-------| [@zou2022]
| Gene Symbol | GLUL |
| Gene Name | Glutamine Synthetase |
| Official Full Name | Glutamate-Ammonia Ligase |
| Chromosomal Location | 1q31.3 |
| GRCh38 Coordinates | chr1:182,375,451-182,392,885 |
| NCBI Gene ID | 2785 |
| OMIM ID | 610012 |
| Ensembl ID | ENSG00000135821 |
| UniProt ID | P15104 |
| Gene Family | Glutamine synthetase family |

</div>}

Overview

The GLUL gene encodes glutamine synthetase (GS), a central enzyme in nitrogen metabolism that catalyzes the ATP-dependent synthesis of glutamine from glutamate and ammonia.^[1] In the brain, glutamine synthetase is essential for glutamate homeostasis, neurotransmitter recycling, and protection against excitotoxicity. It is a key astroglial marker and is implicated in various neurodegenerative diseases.

Function

Enzymatic Activity

Glutamine synthetase catalyzes:^[2]

Glutamate + NH3 + ATP → Glutamine + ADP + Pi

• Reaction type: Ligase (formation of C-N bond)
• Cofactors: ATP, Mg2+, Mn2+
• Subcellular localization: Cytosolic
• Oligomeric state: Decamer (10 subunits)

Brain-Specific Functions

• Converts synaptic glutamate to glutamine
• Prevents excitotoxic glutamate accumulation
• Essential for glutamine-glutamate cycle

• Removes toxic ammonia from brain
• Prevents hepatic encephalopathy
• Critical for neural function

• Protects against oxidative stress
• Maintains redox balance
• Supports neuronal survival

Disease Associations

Neurodegenerative Diseases

Glutamine synthetase is implicated in:^[3]

| Disease | Role |
|---------|------|
| Alzheimer's Disease | Reduced GS in AD brains; impaired glutamate cycling |
| Parkinson's Disease | Astrocytic GS deficiency; excitotoxicity |
| ALS | Motor neuron vulnerability to glutamate toxicity |
| Multiple Sclerosis | Demyelination affects astrocyte function |

Other Conditions

• Hepatic encephalopathy: Ammonia toxicity due to reduced GS
• Stroke: Ischemia reduces GS activity
• Brain trauma: GS as biomarker
• Cancer: GS supports glutamine metabolism in tumors

Common Variants

| Variant | Effect | Clinical Significance |
|---------|--------|----------------------|
| Promoter variants | Altered expression | May modify neurodegeneration risk |
| p.R324C | Missense | Rare, possibly pathogenic |
| p.E286K | Missense | Associated with ALS |

Expression Patterns

• Tissue Distribution: Liver, brain, kidney, muscle
• Brain Expression:
• [Astrocytes](/entities/astrocytes) (highest)
• Oligodendrocytes (lower)
• [Neurons](/entities/neurons) (very low)
• Cellular Localization: Cytosolic
• Isoforms: Brain-specific promoter usage

Interaction Network

GLUL interacts with:

• GLS (Glutaminase) - Complements glutamate metabolism
• GAD1/GAD2 - Glutamate decarboxylase
• EAAT1/GLAST - Glutamate transporter
• EAAT2/GLT-1 - Major glutamate transporter

Therapeutic Targeting

| Approach | Strategy | Status |
|----------|----------|--------|
| Gene therapy | AAV-GLUL delivery | Preclinical |
| Small molecules | GS activators | Research |
| Metabolic modulation | Support glutamine metabolism | In trials |

Key Publications

Background

The study of Glul Gene Glutamine Synthetase has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

References

[@rose2019]: Rose CF, et al. "Glutamine synthetase in brain: regional distribution and regulation." Adv Neurobiol. 2019;23:299-322. PMID: 31647801(https://pubmed.ncbi.nlm.nih.gov/31647801/)
[@albrecht2019]: Albrecht J, et al. "Glutamine synthetase: A key enzyme in ammonia detoxification." Metab Brain Dis. 2019;34(3):797-805. PMID: 30968334(https://pubmed.ncbi.nlm.nih.gov/30968334/)
[@su2021]: Su Y, et al. "Glutamine synthetase deficiency in Alzheimer's disease." Neurobiol Aging. 2021;105:92-104. PMID: 34092254(https://pubmed.ncbi.nlm.nih.gov/34092254/)
[@zou2022]: Zou J, et al. "Targeting glutamine synthetase for neuroprotection." Neuropharmacology. 2022;210:109059. PMID: 35283142(https://pubmed.ncbi.nlm.nih.gov/35283142/)

See Also

• Glutamine Synthetase
• Glutamate
• [Astrocytes](/cell-types/astrocytes)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [NCBI Gene: GLUL](https://www.ncbi.nlm.nih.gov/gene/2785)
• [OMIM: GLUL](https://www.omim.org/entry/610012)
• [UniProt: P15104](https://www.uniprot.org/uniprotkb/P15104)
• [Ensembl: ENSG00000135821](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000135821)

Pathway Diagram

The following diagram shows the key molecular relationships involving GLUL — Glutamine Synthetase discovered through SciDEX knowledge graph analysis: