GO:0004066 asparagine synthase (glutamine-hydrolyzing) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004066 describes the molecular function of asparagine synthase (glutamine-hydrolyzing) activity, which catalyzes the ATP-dependent conversion of L-aspartate and L-glutamine to L-asparagine, L-glutamate, AMP, and diphosphate.
• The enzyme uses a glutamine amidotransferase mechanism, generating a reactive ammonia intermediate that is channeled to the synthetase active site, as demonstrated in Escherichia coli asparagine synthetase B.
• Asparagine synthetase expression is critical for immune cell activation, particularly in CD8+ T cells, where it coordinates with asparagine uptake to support proliferation and effector function.
• In Saccharomyces cerevisiae, asparagine synthetases can localize to the nucleus and associate with the mitotic spindle independently of their enzymatic activity, suggesting moonlighting functions.
• Bacterial asparagine synthetases are regulated by nitrogen availability; for example, the Nac protein represses asnC and asnA transcription in E. coli.
• Studying GO:0004066 requires integrating kinetic, structural, and cellular approaches, including CRISPR-based knockouts, point mutations, and metabolic profiling.
Description
Asparagine synthase (glutamine-hydrolyzing) activity, encoded by GO:0004066, is a fundamental molecular function that enables cells to synthesize the amino acid L-asparagine from L-aspartate using L-glutamine as the nitrogen donor. This reaction is essential for nitrogen assimilation and amino acid homeostasis in bacteria, plants, and mammals. The enzyme belongs to the class of glutamine-dependent amidotransferases, which are characterized by the channeling of ammonia intermediates between distinct active sites. In Escherichia coli, the glutamine-dependent asparagine synthetase B (AsnB) has been extensively studied as a model for understanding the kinetic mechanism and substrate channeling. Beyond its metabolic role, asparagine synthetase is increasingly recognized for its importance in immune cell biology, particularly in T cell activation and proliferation. In Saccharomyces cerevisiae, asparagine synthetases exhibit nuclear localization and mitotic spindle association, hinting at non-enzymatic functions. This article provides a comprehensive overview of GO:0004066, covering its definition, mechanism, key genes, disease relevance, and research methodologies, with a focus on how CRISPR-based models can elucidate its roles.
asparagine synthase (glutamine-hydrolyzing) activity At A Glance
| GO ID | GO:0004066 |
|---|---|
| GO term | asparagine synthase (glutamine-hydrolyzing) activity |
| Ontology | molecular_function |
| Synonym | AS, AS-B activity, asparagine synthetase B activity, glutamine-dependent asparagine synthetase activity, L-aspartate:L-glutamine amido-ligase (AMP-forming) |
| Major function | Catalyzes the ATP-dependent synthesis of L-asparagine from L-aspartate and L-glutamine, producing AMP, diphosphate, and L-glutamate. |
| Reaction | ATP + L-aspartate + L-glutamine = AMP + diphosphate + L-asparagine + L-glutamate |
| EC number | 6.3.5.4 |
| Cofactors | Mg2+ or Mn2+ required for ATP binding and catalysis |
| Subcellular localization | Cytoplasm; also nuclear in some organisms (e.g., S. cerevisiae) |
What Is GO:0004066?
GO:0004066, asparagine synthase (glutamine-hydrolyzing) activity, is defined as the catalysis of the reaction: ATP + L-aspartate + L-glutamine = AMP + diphosphate + L-asparagine + L-glutamate. This activity represents the glutamine-dependent route of asparagine biosynthesis, distinguishing it from ammonia-dependent asparagine synthetases. The enzyme couples the hydrolysis of glutamine to the synthesis of asparagine, using ATP to activate aspartate. This molecular function is conserved across prokaryotes and eukaryotes and is critical for nitrogen metabolism.
Why Is asparagine synthase (glutamine-hydrolyzing) activity Important in Cell Biology?
GO:0004066 is central to nitrogen metabolism and amino acid homeostasis, influencing cell growth, proliferation, and survival. In cancer cells, asparagine synthetase expression is often upregulated to meet the demand for asparagine, and its activity can determine sensitivity to L-asparaginase therapy. In immunology, asparagine synthetase is essential for CD8+ T cell activation, as it coordinates with asparagine uptake to sustain metabolic fitness. The enzyme's mechanism of substrate channeling also serves as a paradigm for understanding interdomain communication in multidomain enzymes. Moreover, bacterial asparagine synthetases are targets for antibiotic development, as they are required for nitrogen assimilation under glutamine-rich conditions. Thus, studying this activity has broad implications for cancer, immunology, and infectious diseases.
• Provides a key route for asparagine biosynthesis, essential for protein synthesis and cell growth.
• Supports CD8+ T cell activation and effector function by maintaining asparagine levels.
• Contributes to cancer cell proliferation and survival, making it a potential therapeutic target.
• Exhibits substrate channeling, a model for understanding enzyme mechanisms.
• Regulated by nitrogen availability in bacteria, impacting nitrogen assimilation.
• Nuclear localization in yeast suggests non-enzymatic roles in mitosis.
• Involved in resistance to L-asparaginase in leukemia.
• Potential target for antimicrobials against bacterial pathogens.
• Used as a model enzyme for studying glutamine amidotransferases.
• Its activity can be modulated by metabolic stress and nutrient availability.
Molecular Mechanism of asparagine synthase (glutamine-hydrolyzing) activity
Substrate Binding and Activation
In simple terms: The enzyme first grabs its substrates, ATP and aspartate, and gets them ready for reaction.
Asparagine synthetase (glutamine-hydrolyzing) binds ATP and L-aspartate in the synthetase domain, forming an aspartyl-AMP intermediate. This step requires divalent cations such as Mg2+ or Mn2+. The glutamine molecule binds in a separate glutaminase domain. The overall reaction is: ATP + L-aspartate + L-glutamine = AMP + diphosphate + L-asparagine + L-glutamate.
Glutamine Hydrolysis and Ammonia Channeling
In simple terms: The enzyme breaks down glutamine to release ammonia, which travels through a tunnel to the other active site.
The glutaminase domain hydrolyzes L-glutamine to L-glutamate and ammonia. The ammonia is not released into the solvent but is channeled through an intramolecular tunnel to the synthetase active site, where it attacks the aspartyl-AMP intermediate to form L-asparagine. This channeling mechanism prevents wasteful hydrolysis of ammonia and is a hallmark of glutamine amidotransferases. Kinetic studies of E. coli AsnB support a ping-pong mechanism with substrate channeling.
Product Release and Enzyme Turnover
In simple terms: After making asparagine, the enzyme releases the products and resets for another cycle.
Following the formation of L-asparagine, the products AMP, diphosphate, L-asparagine, and L-glutamate are released. The enzyme undergoes conformational changes to reset the active sites for subsequent rounds of catalysis. The steady-state kinetic mechanism of E. coli AsnB has been characterized, revealing ordered substrate binding and product release.
Regulation by Nitrogen and Carbon Sources
In simple terms: The enzyme's production is controlled by the availability of nitrogen and carbon in the environment.
In bacteria, asparagine synthetase expression is regulated by nitrogen availability. For instance, in E. coli, the nitrogen assimilation control (Nac) protein represses transcription of asnC and asnA under nitrogen-rich conditions. In Mycobacterium smegmatis, carbon and nitrogen sources influence pyrimidine biosynthesis enzymes, indirectly affecting asparagine metabolism. These regulatory mechanisms ensure that asparagine synthesis is coupled to cellular nitrogen status.
Non-Enzymatic Roles and Localization
In simple terms: In some organisms, the enzyme has additional jobs, like helping with cell division, even without its usual activity.
In Saccharomyces cerevisiae, asparagine synthetases localize to the nucleus and associate with the mitotic spindle independently of their enzymatic activity, suggesting a moonlighting function in mitosis. This indicates that GO:0004066 may have roles beyond catalysis, though the molecular details remain to be fully elucidated.
Key Genes Involved in GO:0004066 asparagine synthase (glutamine-hydrolyzing) activity
The following genes and proteins are directly associated with asparagine synthase (glutamine-hydrolyzing) activity (GO:0004066) or its regulation.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ASNS | Encodes human asparagine synthetase (glutamine-hydrolyzing) | Key enzyme for asparagine synthesis; target in cancer and immunology |
| asnB | Encodes E. coli asparagine synthetase B | Model enzyme for kinetic and structural studies |
| asnA | Encodes E. coli asparagine synthetase A (ammonia-dependent) | Repressed by Nac; contrast with asnB |
| asnC | Regulatory protein for asnA and asnB in E. coli | Repressed by Nac; involved in nitrogen regulation |
| nac | Nitrogen assimilation control protein | Represses asnC and asnA transcription |
| ASN1 | S. cerevisiae asparagine synthetase | Nuclear localization and mitotic spindle association |
| ASN2 | S. cerevisiae asparagine synthetase | Nuclear localization and mitotic spindle association |
| fixT | Sinorhizobium meliloti anti-kinase | Modulated by glutamine amidotransferase-like protein |
| glnA | Glutamine synthetase | Provides glutamine for asparagine synthesis |
| aspC | Aspartate aminotransferase | Supplies aspartate for asparagine synthesis |
| GCN2 | General control nonderepressible 2 kinase | Senses amino acid deprivation, regulates ASNS translation |
| ATF4 | Activating transcription factor 4 | Induces ASNS transcription under stress |
| mTOR | Mechanistic target of rapamycin | Regulates cell growth and ASNS expression |
| MYC | Oncogene | Drives ASNS expression in cancer |
| TP53 | Tumor suppressor | Mutated in cancers, may affect ASNS regulation |
| KEAP1 | Kelch-like ECH-associated protein 1 | Regulates NRF2, which can influence ASNS |
| NRF2 | Nuclear factor erythroid 2-related factor 2 | Transcription factor that may regulate ASNS |
| L-asparaginase | Therapeutic enzyme | Depletes asparagine, targets ASNS-dependent cancers |
How Is asparagine synthase (glutamine-hydrolyzing) activity Regulated?
Asparagine synthetase (glutamine-hydrolyzing) activity is regulated at multiple levels. In bacteria, nitrogen availability controls transcription; for example, the Nac protein represses asnC and asnA in E. coli. In mammalian cells, ASNS expression is induced by amino acid deprivation via the integrated stress response, involving GCN2 and ATF4. Additionally, mTOR signaling promotes cell growth and can influence ASNS expression. In CD8+ T cells, asparagine synthetase expression is coordinated with asparagine uptake to modulate activation. These regulatory mechanisms ensure that asparagine synthesis matches cellular demand.
asparagine synthase (glutamine-hydrolyzing) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ASNS | Acute lymphoblastic leukemia (L-asparaginase resistance) | ASNS knockout or overexpression in leukemia cell lines |
| ASNS | CD8+ T cell activation and immunotherapy | Conditional ASNS knockout in mouse T cells |
| asnB | Bacterial nitrogen assimilation and virulence | asnB deletion in E. coli or Salmonella |
| ASNS | Solid tumors (e.g., pancreatic, ovarian) | ASNS knockdown in cancer cell lines |
| ASNS | Neurological disorders (asparagine metabolism) | Neuron-specific ASNS knockout mice |
Cancer
Asparagine synthetase (ASNS) is often overexpressed in cancers, including leukemia and solid tumors, to sustain asparagine supply for rapid proliferation. High ASNS levels correlate with resistance to L-asparaginase therapy in acute lymphoblastic leukemia. Targeting ASNS or its regulatory pathways is a potential therapeutic strategy.
Immune Disorders
ASNS is critical for CD8+ T cell activation; its deficiency impairs T cell proliferation and effector function. This has implications for immunotherapy and autoimmune diseases.
Infectious Diseases
Bacterial asparagine synthetases are essential for nitrogen assimilation and virulence. Inhibitors of these enzymes could serve as novel antibiotics.
Neurological Disorders
Asparagine is a precursor for neurotransmitters; dysregulation of ASNS may contribute to neurological conditions, though direct evidence is limited.
From asparagine synthase (glutamine-hydrolyzing) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does ASNS loss affect T cell activation? | Conditional ASNS knockout in mouse CD8+ T cells |
| What is the kinetic mechanism of AsnB? | Point mutations in E. coli asnB active sites |
| Does nuclear localization of yeast ASN1 require enzymatic activity? | ASN1 point mutants (active-site) in S. cerevisiae |
| Can ASNS overexpression confer L-asparaginase resistance? | ASNS overexpression in leukemia cell lines |
| What is the role of Nac in asnA/asnB regulation? | nac knockout in E. coli |
| Does ASNS channeling require interdomain tunnel? | Knock-in of tunnel-blocking mutations in ASNS |
How to Study the asparagine synthase (glutamine-hydrolyzing) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Enzymatic assay | Asparagine synthesis or glutamate release | Kinetic characterization of ASNS |
| Metabolomics | Intracellular asparagine, aspartate, glutamine, glutamate | Metabolic flux analysis |
| RNA-seq | ASNS mRNA levels | Transcriptional regulation studies |
| Ribo-seq | Translation efficiency of ASNS | Translational control under stress |
| Western blot | ASNS protein levels | Expression analysis |
| Immunofluorescence | Subcellular localization | Nuclear/mitotic spindle localization |
| CRISPR knockout | Loss of ASNS function | Phenotypic studies |
| Site-directed mutagenesis | Specific residues in active sites | Mechanistic studies |
Enzymatic Assays
Asparagine synthetase activity can be measured using coupled assays that monitor the formation of L-asparagine or the consumption of ATP. For glutamine-dependent activity, the release of L-glutamate can be quantified. These assays are essential for kinetic characterization.
Metabolic Profiling
Mass spectrometry-based metabolomics can quantify asparagine, aspartate, glutamine, and glutamate levels in cells or tissues, providing insights into flux through the pathway.
Transcriptional and Translational Analysis
RNA-seq and Ribo-seq can measure ASNS mRNA and translation efficiency under different conditions, such as amino acid deprivation or immune activation.
Imaging and Localization
Fluorescence microscopy of tagged ASNS (e.g., GFP) can reveal subcellular localization, including nuclear and mitotic spindle association in yeast.
How CRISPR Can Be Used to Study GO:0004066 asparagine synthase (glutamine-hydrolyzing) activity
Knockout
CRISPR-Cas9 knockout of ASNS can be used to study its role in cell proliferation, T cell activation, and cancer cell survival. For example, ASNS knockout in CD8+ T cells impairs activation and effector function. In bacteria, asnB knockout can assess nitrogen assimilation defects.
Point Mutation
Point mutations in catalytic residues of ASNS (e.g., in the glutaminase or synthetase domains) can dissect the mechanism of substrate channeling and catalysis. Such mutations in E. coli asnB have been used to probe the role of specific residues in ammonia transfer.
Knock-in
Knock-in of tagged ASNS (e.g., GFP or FLAG) allows for localization and interaction studies. In yeast, knock-in of tagged ASN1/ASN2 revealed nuclear and mitotic spindle localization. Knock-in of disease-associated mutations can model human disorders.
Overexpression
Overexpression of ASNS via CRISPR activation or lentiviral vectors can model L-asparaginase resistance in leukemia and study the effects of elevated asparagine synthesis on cell growth and metabolism.
How EDITGENE Supports asparagine synthase (glutamine-hydrolyzing) activity Research
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Frequently Asked Questions About asparagine synthase (glutamine-hydrolyzing) activity
What is asparagine synthase (glutamine-hydrolyzing) activity?
It is a molecular function (GO:0004066) that catalyzes the ATP-dependent synthesis of L-asparagine from L-aspartate and L-glutamine, producing AMP, diphosphate, and L-glutamate.
What genes are involved in asparagine synthase (glutamine-hydrolyzing) activity?
Key genes include ASNS in humans, asnB in E. coli, and ASN1/ASN2 in S. cerevisiae.
What is the reaction catalyzed by GO:0004066?
ATP + L-aspartate + L-glutamine = AMP + diphosphate + L-asparagine + L-glutamate.
How is asparagine synthetase regulated?
It is regulated by nitrogen availability in bacteria via Nac, and by amino acid stress via GCN2/ATF4 in mammals.
Why is asparagine synthetase important in cancer?
It supports cancer cell proliferation and resistance to L-asparaginase therapy.
What is the role of ASNS in T cells?
ASNS coordinates with asparagine uptake to modulate CD8+ T cell activation and effector function.
Does asparagine synthetase have non-enzymatic functions?
In yeast, it localizes to the nucleus and mitotic spindle independently of enzymatic activity.
What methods are used to study GO:0004066?
Enzymatic assays, metabolomics, RNA-seq, Ribo-seq, imaging, and CRISPR-based perturbations.
What is substrate channeling in asparagine synthetase?
It is the direct transfer of ammonia from the glutaminase domain to the synthetase domain, preventing ammonia loss.
How can CRISPR help study asparagine synthase?
CRISPR knockout, point mutation, knock-in, and overexpression models can reveal gene function and mechanism.
Conclusion
Asparagine synthase (glutamine-hydrolyzing) activity (GO:0004066) is a vital molecular function with broad implications in metabolism, immunity, and disease. Its mechanism of substrate channeling and regulation by nitrogen status exemplify fundamental principles of enzyme catalysis. Continued research using CRISPR-based models will further illuminate its roles and therapeutic potential.
References
- 1. Hope HC et al.. 2021. Coordination of asparagine uptake and asparagine synthetase expression modulates CD8+ T cell activation.. JCI Insight 6(9) PMID: 33822775
- 2. Tesson AR et al.. 2003. Revisiting the steady state kinetic mechanism of glutamine-dependent asparagine synthetase from Escherichia coli.. Arch Biochem Biophys 413(1):23-31 PMID: 12706338
- 3. Huang X et al.. 2001. Channeling of substrates and intermediates in enzyme-catalyzed reactions.. Annu Rev Biochem 70:149-80 PMID: 11395405
- 4. Noree C et al.. 2020. Nuclear targeted Saccharomyces cerevisiae asparagine synthetases associate with the mitotic spindle regardless of their enzymatic activity.. PLoS One 15(12):e0243742 PMID: 33347445
- 6. Poggio S et al.. 2002. The nitrogen assimilation control (Nac) protein represses asnC and asnA transcription in Escherichia coli.. FEMS Microbiol Lett 206(2):151-6 PMID: 11814655
- 8. Masood R et al.. 1987. Role of various carbon and nitrogen sources in the regulation of enzymes of pyrimidine biosynthesis in Mycobacterium smegmatis TMC 1546.. Ann Inst Pasteur Microbiol 138(5):501-7 PMID: 3440089
