GLUL — Glutamine Synthetase

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gene2324 wordssynced 2026-04-02

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

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

The enzyme requires multiple cofactors for activity:

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:

Glutamate activation: Glutamate + ATP → γ-glutamyl phosphate + ADP

Ammonia addition: γ-glutamyl phosphate + NH₃ → Glutamine + Pi

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/)):

Neurotransmitter Recycling: After synaptic release, glutamate is taken up by astrocytes

Glutamine Synthesis: Astrocytic GS converts glutamate to glutamine

Glutamine Release: Glutamine is released from astrocytes and taken up by neurons

Glutamate Reformation: Neuronal glutaminase converts glutamine back to glutamate

Vesicular Packaging: Glutamate is re-packaged into synaptic vesicles

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:

Impaired Glutamate Uptake: Reduced astrocytic glutamate clearance

Extracellular Glutamate Accumulation: Pathologically elevated glutamate levels

NMDA Receptor Overactivation: Enhanced Ca²⁺ influx

Oxidative Stress: ROS production and mitochondrial dysfunction

Apoptotic Pathways: Caspase activation and cell death

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:

GS Regulation: What controls astrocytic GS expression?

Therapeutic Target: Which GS function is most critical for neuroprotection?

Cell Type Specificity: Why do astrocytes require high GS?

Biomarkers: Can GS be used to track disease progression?

Astrocyte-Neuron Coupling: How does GS affect metabolic support?

Key Publications

[Rose CF, et al. Glutamine synthetase in brain: regional distribution and regulation (2019)](https://pubmed.ncbi.nlm.nih.gov/31647801/). Adv Neurobiol.

[Albrecht J, et al. Glutamine synthetase: a key enzyme in ammonia detoxification (2019)](https://pubmed.ncbi.nlm.nih.gov/30968334/). Metab Brain Dis.

[Su Y, et al. Glutamine synthetase deficiency in Alzheimer's disease (2021)](https://pubmed.ncbi.nlm.nih.gov/34092254/). Neurobiol Aging.

[Zou J, et al. Targeting glutamine synthetase for neuroprotection (2022)](https://pubmed.ncbi.nlm.nih.gov/35283142/). Neuropharmacology.

[Norenberg MD, et al. The glutamine synthetase in brain: the roles in astrocytes (2010)](https://pubmed.ncbi.nlm.nih.gov/21059219/). ASN Neuro.

[Martinez J, et al. Glutamine synthetase in health and disease (2019)](https://pubmed.ncbi.nlm.nih.gov/30506178/). J Neurochem.

[Schousboe A, et al. The glutamate/GABA-glutamine cycle (2019)](https://pubmed.ncbi.nlm.nih.gov/30604225/). Neurochem Res.

[Yang S, et al. Targeting astrocytic GS for Parkinson's disease therapy (2022)](https://pubmed.ncbi.nlm.nih.gov/35054178/). Acta Neuropathol.

[Kim J, et al. Astrocyte-neuron metabolic coupling via GS (2023)](https://pubmed.ncbi.nlm.nih.gov/37088921/). Nat Metab.

Pathway & Interaction Diagram

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

Mermaid diagram (expand to render)

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.<sup>[1]</sup> 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:<sup>[2]</sup>

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

Glutamate homeostasis

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

Ammonia detoxification

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

Neuroprotection

Protects against oxidative stress
Maintains redox balance
Supports neuronal survival

Disease Associations

Neurodegenerative Diseases

Glutamine synthetase is implicated in:<sup>[3]</sup>

| 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

Cooper AJ, et al. "Glutamine synthetase in brain." Neurochem Res. 2015;40(3):511-525.

Rose CF, et al. "Brain glutamine synthetase in hepatic encephalopathy." Metab Brain Dis. 2013;28(2):193-197.

McKenna MC, et al. "Glutamate metabolism in brain." Neurochem Res. 2012;37(11):2439-2455.

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/)

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)

Last updated: March 2026

Pathway Diagram

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

Mermaid diagram (expand to render)

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GLUL — Glutamine Synthetase

GLUL — Glutamine Synthetase

GLUL — Glutamine Synthetase

GLUL — Glutamine Synthetase

Overview

Gene Structure and Protein Domain Architecture

Genomic Organization

Protein Domain Structure

Normal Biological Functions

Enzymatic Activity and Reaction

Glutamate Homeostasis and the Glutamine-Glutamate Cycle

Ammonia Detoxification

Astrocytic Functions

Neuroprotection

Role in Neurodegenerative Diseases

Alzheimer's Disease

Parkinson's Disease

Amyotrophic Lateral Sclerosis

Epilepsy

Multiple Sclerosis

Molecular Mechanisms

Excitotoxicity and Glutamate Homeostasis

Ammonia Toxicity

Astrocyte-Neuron Metabolic Coupling

Therapeutic Approaches

Small Molecule Activators

Gene Therapy

Metabolic Modulation

Repurposed Drugs

Genetics and Population Studies

Disease-Associated Variants

Congenital Glutamine Deficiency

Population Genetics

Animal Models

Mouse Models

Zebrafish Models

Diagnosis and Testing

Genetic Testing

Biomarkers

Research Directions

Key Publications

Pathway & Interaction Diagram

See Also

External Links

GLUL Gene

Introduction

Overview

Function

Enzymatic Activity

Brain-Specific Functions

Disease Associations

Neurodegenerative Diseases

Other Conditions

Common Variants

Expression Patterns

Interaction Network

Therapeutic Targeting

Key Publications

Background

References

See Also

External Links

Pathway Diagram