ASCT2 Protein (Alanine-Serine-Cysteine Transporter 2)
Overview
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">ASCT2 Protein (Alanine-Serine-Cysteine Transporter 2)</th>
</tr>
<tr>
<td class="label">Substrate</td>
<td>Km (μM)</td>
</tr>
<tr>
<td class="label">Glutamine</td>
<td>~100</td>
</tr>
<tr>
<td class="label">Serine</td>
<td>~50</td>
</tr>
<tr>
<td class="label">Alanine</td>
<td>~200</td>
</tr>
<tr>
<td class="label">Cysteine</td>
<td>~150</td>
</tr>
<tr>
<td class="label">Threonine</td>
<td>~100</td>
</tr>
<tr>
<td class="label">Asparagine</td>
<td>~80</td>
</tr>
<tr>
<td class="label">Gene Variant</td>
<td>Effect</td>
</tr>
<tr>
<td class="label">SLC1A5 variants</td>
<td>Altered transport</td>
</tr>
<tr>
<td class="label">Expression changes</td>
<td>Modified glutamine flux</td>
</tr>
<tr>
<td class="label">Partner</td>
<td>Interaction Type</td>
</tr>
<tr>
<td class="label">mTORC1</td>
<td>Amino acid sensing</td>
</tr>
<tr>
<td class="label">Glutamine synthetase</td>
<td>Substrate supply</td>
</tr>
<tr>
<td class="label">EAAT1/2</td>
<td>Glutamate transport</td>
</tr>
<tr>
<td class="label">System L (LAT1)</td>
<td>Exchange partner</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">3 edges</a></td>
</tr>
</table>
ASCT2 (SLC1A5, System A Amino Acid Transporter 2) is a sodium-dependent neutral amino acid transporter that plays critical roles in cellular metabolism, particularly in the exchange of amino acids required for tumor cell growth, neuronal function, and immune responses[@kanai2013]. ASCT2 is a member of the SLC1 (solute carrier family 1) transporter family and functions as a high-affinity transporter for glutamine, serine, alanine, cysteine, and other small neutral amino acids[@broer2015]. In the central nervous system, ASCT2 is essential for maintaining glutamine cycles between astrocytes and neurons, with significant implications for neurotransmitter biosynthesis and neuronal metabolism[@balk2007].
Protein Structure
ASCT2 is a multipass transmembrane protein with the following structural features:
- Primary Structure: 541 amino acids, molecular weight ~56 kDa
- Transmembrane Architecture: 8-10 transmembrane alpha-helical domains
- Aspartate Residue (D455): Critical for substrate binding and transport kinetics
- Oligomeric State: Functions as a homotrimer in the plasma membrane
Transport Mechanism
ASCT2 operates as an obligatory exchange transporter:
- Stoichiometry: Na+:substrate = 1:1
- Transport Mode: Obligatory exchange (antiport)
- Direction: Typically imports neutral amino acids in exchange for intracellular substrates
- Electrogenicity: Net negative charge per transport cycle
ASCT2 Transport Mechanism
┌──────────────────────────────────────┐
│ Cell Membrane │
│ ┌─────────┐ ┌─────────────┐ │
│ │ Extracel │ │ Intracellular│ │
│ │ lular │◄──────►│ │ │
│ │ │ │ │ │
│ │ Gln, Ser│ │ Internal │ │
│ │ Ala, Cys│ │ amino acids │ │
│ └─────────┘ └─────────────┘ │
│ ↑ │ │
│ └──── Na+ (co-transport)┘ │
└──────────────────────────────────────┘
Normal Biological Function
Amino Acid Transport
ASCT2 transports a wide range of neutral amino acids with varying affinities:
Glutamine Transport and Metabolism:
- Provides glutamine for de novo synthesis of nucleotides and amino acids
- Supports mTORC1 activation through glutamine sensing
- Enables glutathione synthesis through cysteine import
- Regulates intracellular amino acid pools
mTORC1 Activation:
- Glutamine import via ASCT2 is essential for mTORC1 signaling
- Serves as an amino acid sensor for cell growth
- Integrates nutrient signaling with cellular metabolism
Glutathione Synthesis:
- Imports cysteine (rate-limiting precursor)
- Supports antioxidant defense in neurons and glia
Tissue Distribution
- High Expression: Kidney, intestine, liver, placenta
- Brain: [Astrocytes](/entities/astrocytes) and [neurons](/entities/neurons), particularly in glutamatergic neurons
- Immune Cells: Activated T cells and natural killer cells
- Cancer Cells: Frequently upregulated in tumors (Warburg effect)
Role in Neurodegeneration
Alzheimer's Disease
ASCT2 dysfunction contributes to multiple aspects of AD pathogenesis:
Glutamine Transport Alterations:
- ASCT2 expression is downregulated in AD brain[@zhang2019]
- Impaired glutamine transport affects neuronal metabolism
- Disrupted glutamate/GABA cycling between astrocytes and neurons
- Altered neurotransmitter precursor availability
Metabolic Dysregulation:
- Reduced mTORC1 signaling in neurons
- Impaired glutathione synthesis increases oxidative stress
- Defective amino acid sensing affects protein synthesis
Therapeutic Implications:
- ASCT2 activators may improve neuronal metabolism
- Glutamine supplementation strategies
- Antioxidant therapies targeting glutathione synthesis
Parkinson's Disease
In [Parkinson's disease](/diseases/parkinsons-disease), ASCT2 plays critical roles:
Dopaminergic Neuron Metabolism:
- Glutamine transport is essential for dopamine synthesis
- ASCT2 dysfunction may contribute to energy deficits
- Altered cysteine import affects glutathione maintenance
Neuroinflammation:
- Microglial ASCT2 supports inflammatory responses
- Astrocyte dysfunction in PD
- Glutamine cycle disruption affects neurotransmitter homeostasis
Potential Therapeutic Targets:
- Modulating ASCT2 expression or activity
- Glutamine precursor administration
- Enhancing antioxidant defenses
Amyotrophic Lateral Sclerosis (ALS)
- Motor neuron metabolism dependence on ASCT2
- Astrocyte support of motor neurons through glutamine transport
- Energy metabolism alterations in ALS
Huntington's Disease
- Altered amino acid transport in HD brain
- Metabolic dysfunction contributing to neuronal loss
- Glutamine cycle abnormalities
Genetic Associations
Protein Interactions
Expression Patterns in the Brain
Cellular Distribution
- Astrocytes: High expression, especially in perisynaptic processes
- Neurons: Moderate expression, highest in glutamatergic neurons
- Oligodendrocytes: Lower expression
- [Microglia](/cell-types/microglia-neuroinflammation): Variable, increases with activation
Regulation
- Transcriptional: mTORC1-dependent upregulation
- Post-translational: Phosphorylation affects transport activity
- Substrate-induced: Activity regulated by amino acid levels
Therapeutic Implications
Small Molecule Modulators
Glutamine analogs: Substrate-based inhibitors
ASCT2 activators: Enhance transport function
Amino acid derivatives: Targeted at transport kinetics
- L-Glutamine supplementation: Bypass transport deficits
- N-acetylcysteine: Increase cysteine availability
- Alpha-ketoglutarate: Support metabolic function
- [Glutamate-Glutamine Cycle](/mechanisms/glutamate-glutamine-cycle)
- [GABA Synthesis Pathway](/mechanisms/gaba-synthesis)
- [mTOR Signaling](/mechanisms/mtor-signaling-pathway)
- [Antioxidant Response](/mechanisms/nrf2-antioxidant-pathway)
- [Neuroinflammation](/mechanisms/neuroinflammation)
- [EAAT1 (SLC1A3) Gene](/genes/slc1a3)
- [EAAT2 (SLC1A2) Gene](/genes/slc1a2)
- [Glutamine Synthetase](/proteins/glutamine-synthetase)
- [mTOR Protein](/proteins/mtor-protein)
- [GFAP Protein](/entities/glial-fibrillary-acidic-protein)
Pathway & Interaction Diagram
Interactive diagram showing ASCT2's key relationships in the SciDEX knowledge graph (6 connections shown).
Mermaid diagram (expand to render)
See Also
- [Glutamate-Glutamine Cycle](/mechanisms/glutamate-glutamine-cycle)
- [GABA Synthesis Pathway](/mechanisms/gaba-synthesis)
- [mTOR Signaling](/mechanisms/mtor-signaling-pathway)
- [Antioxidant Response](/mechanisms/nrf2-antioxidant-pathway)
- [Neuroinflammation](/mechanisms/neuroinflammation)
External Links
- [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
- [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)
References
[Kanai et al., SLC1A5/ASCT2 as a glutamine transporter (2013) (2013)](https://pubmed.ncbi.nlm.nih.gov/23469221/)
[Broer et al., ASCT2 structure and function (2015) (2015)](https://pubmed.ncbi.nlm.nih.gov/25825768/)
[Balk et al., Brain amino acid transport (2007) (2007)](https://pubmed.ncbi.nlm.nih.gov/17656472/)
[Zhang et al., ASCT2 in AD brain (2019) (2019)](https://pubmed.ncbi.nlm.nih.gov/31154988/)
[Unknown, Broer, ASCT2 in cancer metabolism (2014) (2014)](https://pubmed.ncbi.nlm.nih.gov/24698258/)