GO:0003883 CTP synthase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0003883 (CTP synthase activity) catalyzes the ATP-dependent conversion of UTP and glutamine to CTP and glutamate, the final step of de novo pyrimidine nucleotide synthesis.
• CTP synthase is encoded by CTPS1 and CTPS2 in humans; CTPS2 regulates CTP synthetase activity by interacting with CTPS1.
• The enzyme forms filamentous structures called cytoophidia, and filament formation is tightly coupled to its catalytic activity.
• CTPS1 is essential for T-cell proliferation and is a candidate therapeutic target in lymphoid malignancies and immune disorders.
• Bacterial CTP synthase (PyrG) is a validated antibacterial target, as shown by crizotinib-mediated inhibition in Gram-positive bacteria.
• CRISPR knockout, point-mutation, knock-in, and overexpression models enable causal dissection of CTP synthase function in cancer, immunity, and metabolism.
Description
CTP synthase activity (GO:0003883) is the enzymatic function that produces cytidine 5'-triphosphate (CTP), the rate-limiting step of de novo pyrimidine biosynthesis. The reaction consumes ATP, UTP, and glutamine and releases ADP, phosphate, CTP, and glutamate, linking nucleotide metabolism to energy status and nitrogen handling. Because CTP is required for DNA and RNA synthesis, phospholipid metabolism, and sialylation, this activity sits at the crossroads of proliferation and biosynthetic demand. In humans, CTP synthase is encoded by two genes, CTPS1 and CTPS2, whose protein products can interact and regulate each other's catalytic output. Beyond its catalytic role, CTP synthase assembles into filamentous structures termed cytoophidia, a property conserved from bacteria to humans and coupled to enzyme activity. This dual nature, a soluble enzyme and a polymer, has made CTP synthase a model for studying metabolic enzyme assembly and its physiological consequences. Researchers study GO:0003883 to understand how cells balance nucleotide supply with demand, how this balance is rewired in cancer and immune activation, and how it can be targeted in infectious disease.
CTP synthase activity At A Glance
| GO ID | GO:0003883 |
|---|---|
| GO term | CTP synthase activity |
| Ontology | molecular_function |
| Synonym | CTP synthetase activity; cytidine 5'-triphosphate synthetase activity; cytidine triphosphate synthetase activity; uridine triphosphate aminase activity; UTP--ammonia ligase activity; UTP:ammonia ligase (ADP-forming) |
| Major function | Catalyzes ATP + UTP + glutamine + H2O = ADP + phosphate + CTP + glutamate |
| Human genes | CTPS1, CTPS2 |
| Bacterial gene | pyrG |
| Substrates | ATP, UTP, glutamine, H2O |
| Products | ADP, phosphate, CTP, glutamate |
| Structural hallmark | Filamentous polymers called cytoophidia |
What Is GO:0003883?
GO:0003883, CTP synthase activity, is defined by QuickGO as the catalysis of the reaction ATP + UTP + glutamine + H2O = ADP + phosphate + CTP + glutamate. In other words, it is the molecular function that uses the energy of ATP hydrolysis and the amide nitrogen of glutamine to convert uridine triphosphate (UTP) into cytidine triphosphate (CTP). This activity is synonymous with CTP synthetase activity, cytidine 5'-triphosphate synthetase activity, cytidine triphosphate synthetase activity, uridine triphosphate aminase activity, UTP--ammonia ligase activity, and UTP:ammonia ligase (ADP-forming) activity. It belongs to the molecular_function ontology aspect and is executed by CTP synthase enzymes such as CTPS1 and CTPS2 in humans and PyrG in bacteria.
Why Is CTP synthase activity Important in Cell Biology?
CTP synthase activity is important because it controls the cellular pool of CTP, a nucleotide required for nucleic acid synthesis, phospholipid metabolism, and protein glycosylation. Its catalytic output is essential for the proliferation of activated lymphocytes, and CTPS1 deficiency causes a severe immunodeficiency characterized by impaired T-cell expansion. In cancer, elevated CTP synthase activity supports the biosynthetic demands of rapidly dividing cells, making it a candidate target for antimetabolite and small-molecule strategies. In bacteria, the CTP synthase PyrG is required for growth, and its inhibition by crizotinib reduces ATP production and viability in Gram-positive pathogens. The enzyme's ability to polymerize into cytoophidia adds a layer of regulation that links metabolic state to higher-order assembly, a phenomenon studied in Drosophila, human cells, and bacteria. Consequently, GO:0003883 is relevant to immunology, oncology, microbiology, and structural biology, and it is a frequent subject of CRISPR-based functional genomics.
• Provides the final step of de novo pyrimidine synthesis, supplying CTP for DNA and RNA.
• Supports T-cell proliferation and adaptive immunity; CTPS1 loss causes immunodeficiency.
• Is a metabolic vulnerability in lymphoid malignancies and other proliferative disorders.
• Forms cytoophidia, linking enzyme activity to filament assembly and cellular organization.
• Is a validated antibacterial target in Gram-positive bacteria via PyrG inhibition.
• Connects Ras signaling to nucleotide metabolism in Drosophila models.
• CTPS2 modulates CTPS1 activity through direct protein-protein interaction.
• Serves as a paradigm for studying metabolic enzyme polymerization and its regulation.
What Happens During CTP synthase activity?
Substrate binding and glutamine hydrolysis
In simple terms: The enzyme first grabs its raw materials and splits glutamine to get the nitrogen it needs.
CTP synthase binds ATP, UTP, and glutamine in an ordered manner. The glutamine amide is hydrolyzed in the glutaminase domain, generating glutamate and an activated ammonia intermediate that is channeled to the synthase active site. This step couples nitrogen donation to the subsequent phosphorylation of UTP.
UTP phosphorylation and CTP formation
In simple terms: The enzyme then uses ATP to add a phosphate-derived group to UTP, turning it into CTP.
In the synthase domain, ATP phosphorylates the UTP intermediate, yielding CTP, ADP, and phosphate. The reaction is the terminal step of de novo pyrimidine biosynthesis, and its product CTP feedback-inhibits the pathway. Structural studies of bifunctional CTP/dCTP synthases have revealed how the active site accommodates both UTP and dUTP substrates.
Filament assembly and cytoophidium formation
In simple terms: Many enzyme molecules can stack together into long fibers called cytoophidia.
CTP synthase polymerizes into filamentous structures termed cytoophidia, which are observed in bacteria, yeast, Drosophila, and human cells. Filament formation is regulated in concert with catalytic activity, and the N-terminal region of the enzyme is critical for cytoophidium assembly. Recent work shows that hCTPS1 filamentation is influenced by CTP binding, linking product availability to polymer stability.
Regulation by CTPS1-CTPS2 interaction
In simple terms: Two related proteins, CTPS1 and CTPS2, can work together to tune how much CTP is made.
Human cells express CTPS1 and CTPS2, and CTPS2 regulates CTP synthetase activity by interacting with CTPS1. This interaction modulates the catalytic output of the complex and may influence tissue-specific CTP production. The existence of two isoforms with distinct regulation adds complexity to how cells maintain CTP homeostasis.
Key Genes Involved in GO:0003883 CTP synthase activity
The following genes and proteins are directly implicated in CTP synthase activity (GO:0003883) or its regulation, as supported by the cited literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CTPS1 | Human CTP synthase 1; catalyzes UTP to CTP conversion | Immunodeficiency, T-cell proliferation, cancer metabolism |
| CTPS2 | Human CTP synthase 2; interacts with CTPS1 to regulate activity | Isoform-specific regulation of CTP synthesis |
| pyrG | Bacterial CTP synthase | Antibacterial target; inhibited by crizotinib |
| CTPS | Drosophila CTP synthase | Cytoophidium assembly and Ras signaling studies |
| Ras | Small GTPase signaling protein | Links growth signaling to CTP synthase in Drosophila |
| CTPS (yeast) | Yeast CTP synthase | Model for filament formation and enzyme regulation |
| hCTPS1 | Human CTPS1 filamentous form | Structural basis of filamentation with CTP |
| CTP/dCTP synthase | Bifunctional enzyme in some organisms | Structural basis of dual substrate specificity |
| N-terminal domain | Region required for cytoophidium assembly | Filament formation studies |
| Glutaminase domain | Hydrolyzes glutamine to supply nitrogen | Catalytic mechanism studies |
| Synthase domain | Phosphorylates UTP to form CTP | Catalytic mechanism studies |
| CTPS1-CTPS2 complex | Heteromeric enzyme complex | Regulation of CTP synthetase activity |
| PyrG (Gram-positive) | Bacterial CTP synthase | Crizotinib antibacterial activity |
| Cytoophidium | Filamentous polymer of CTP synthase | Metabolic enzyme assembly |
| CTP | Product and feedback inhibitor | Allosteric regulation of enzyme |
| UTP | Substrate for CTP synthesis | Nucleotide metabolism |
| Glutamine | Nitrogen donor | Amino acid metabolism |
| ATP | Phosphate donor and energy source | Energy coupling |
How Is CTP synthase activity Regulated?
CTP synthase activity is regulated at multiple levels. Catalytically, the enzyme is feedback-inhibited by its product CTP, which binds to the active site and reduces flux through the pathway. In humans, CTPS2 interacts with CTPS1 to modulate CTP synthetase activity, providing an isoform-specific regulatory mechanism. Filament formation (cytoophidium assembly) is also coupled to enzyme activity, and the N-terminal region of the protein is required for this polymerization. In Drosophila, Ras signaling influences CTP synthase, linking growth factor pathways to nucleotide metabolism. Additionally, CTP binding affects hCTPS1 filamentation, suggesting that product levels directly influence polymer stability. Together, these mechanisms ensure that CTP production matches cellular demand for nucleic acid synthesis and other biosynthetic processes.
CTP synthase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CTPS1 | Severe combined immunodeficiency; T-cell proliferation defect | CTPS1 knockout T cells; patient-derived lymphocytes |
| CTPS1 | Lymphoid malignancies; metabolic vulnerability | CTPS1 overexpression in cancer cell lines; xenografts |
| CTPS2 | Modifier of CTPS1 activity; immune regulation | CTPS2 knockout and CTPS1-CTPS2 double knockout |
| pyrG | Bacterial growth and infection | pyrG knockout in Gram-positive bacteria; crizotinib treatment |
| CTPS (Drosophila) | Ras-driven growth and cytoophidium formation | Drosophila CTPS mutants; Ras overexpression |
CTP synthase activity in immunodeficiency
Biallelic mutations in CTPS1 cause a severe combined immunodeficiency characterized by impaired T-cell proliferation and recurrent infections. The enzyme is essential for activated lymphocytes to expand, and loss of CTPS1 activity blocks their ability to synthesize CTP at the required rate. CTPS2 can partially compensate in some tissues, but its interaction with CTPS1 is critical for full activity. This makes CTP synthase a key node in immune cell metabolism and a potential target for immunomodulation.
CTP synthase activity in cancer
Cancer cells often upregulate nucleotide synthesis to support rapid proliferation, and CTP synthase activity is a component of this metabolic rewiring. Elevated CTP production supports DNA replication and RNA synthesis, and inhibition of CTP synthase can reduce tumor cell growth in preclinical models. The enzyme's filamentous form, the cytoophidium, has been observed in cancer cells and may serve as a marker of metabolic activity. Targeting CTP synthase is therefore an area of interest for antimetabolite and small-molecule drug development.
CTP synthase activity in bacterial infection
In bacteria, CTP synthase (PyrG) is essential for growth and is a validated antibacterial target. Crizotinib, a clinically approved kinase inhibitor, was shown to inhibit Gram-positive bacterial growth by reducing ATP production and targeting PyrG. This repurposing approach highlights the potential of CTP synthase inhibitors as antibiotics. Structural differences between bacterial and human CTP synthases may allow selective targeting.
From CTP synthase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of CTPS1 abolish T-cell proliferation? | CTPS1 knockout in Jurkat or primary T cells |
| Does a point mutation in the catalytic site eliminate CTP synthesis? | CRISPR point mutation of CTPS1 active-site residues |
| Does tagging CTPS1 with GFP affect cytoophidium formation? | Knock-in of fluorescent tag at endogenous CTPS1 locus |
| Does CTPS2 overexpression alter CTP levels? | CTPS2 overexpression in HEK293 or cancer cell lines |
| Does CTPS1 overexpression drive proliferation? | CTPS1 overexpression in primary fibroblasts or cancer cells |
| Does bacterial PyrG inhibition reduce ATP production? | pyrG knockout or crizotinib treatment in Gram-positive bacteria |
How to Study the CTP synthase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Enzymatic assay | CTP production from UTP | Validation of CTPS1/CTPS2 activity |
| Fluorescence microscopy | Cytoophidium number and morphology | Filament assembly studies |
| LC-MS metabolomics | Intracellular nucleotide pools | Metabolic impact of CTP synthase edits |
| CRISPR knockout screening | Gene essentiality and synthetic lethality | Identifying CTP synthase vulnerabilities |
| Western blot | Protein expression levels | Confirming knockout or overexpression |
| qRT-PCR | mRNA expression of CTPS1/CTPS2 | Transcriptional regulation studies |
| Structural biology (cryo-EM) | Filament and active-site architecture | Mechanistic studies of CTP synthase |
| Bacterial growth assay | PyrG inhibition | Antibacterial drug testing |
Enzymatic assays for CTP synthase activity
CTP synthase activity can be measured using coupled enzymatic assays that monitor the conversion of UTP to CTP, often by HPLC or spectrophotometric detection of NADH oxidation. Radioactive or fluorescently labeled UTP can be used to quantify product formation in cell lysates or purified enzyme preparations. These assays are essential for validating the functional impact of CRISPR edits.
Imaging cytoophidia
Fluorescence microscopy of GFP- or mCherry-tagged CTP synthase allows visualization of cytoophidia in live cells. The number, length, and distribution of filaments can be quantified under different metabolic conditions or after genetic perturbation. This method links enzyme activity to higher-order assembly.
Metabolomics and nucleotide profiling
Liquid chromatography-mass spectrometry (LC-MS) can quantify intracellular CTP, UTP, ATP, and other nucleotides to assess the impact of CTP synthase perturbations. Metabolomic profiling reveals how changes in CTP synthase activity affect broader nucleotide pools and biosynthetic pathways.
CRISPR screening and functional genomics
Genome-wide CRISPR knockout screens can identify genes that modulate sensitivity to CTP synthase inhibitors or that are synthetic lethal with CTPS1 loss. Such screens help uncover pathways that compensate for reduced CTP synthesis and identify combination therapy targets.
How CRISPR Can Be Used to Study GO:0003883 CTP synthase activity
Knockout
CRISPR knockout of CTPS1 or CTPS2 in human cell lines can abolish CTP synthase activity and reveal essentiality in proliferation and survival. Knockout models are used to study immunodeficiency mechanisms and to validate drug targets. In bacteria, pyrG knockout confirms essentiality and is used to test antibacterial compounds.
Point Mutation
Point mutations in the catalytic domains of CTPS1 can dissect the roles of specific residues in glutamine hydrolysis or UTP phosphorylation. Such mutations can also be used to create separation-of-function alleles that retain filament formation but lose catalytic activity, or vice versa. These models help distinguish catalytic from structural functions.
Knock-in
Knock-in of fluorescent tags (e.g., GFP) at the endogenous CTPS1 locus enables real-time imaging of cytoophidia without overexpression artifacts. Knock-in of disease-associated mutations can model immunodeficiency or cancer-associated variants. This approach preserves endogenous regulatory elements and expression levels.
Overexpression
Overexpression of CTPS1 or CTPS2 in cell lines can increase CTP levels and drive proliferation, mimicking the metabolic state of cancer cells. Overexpression models are useful for testing CTP synthase inhibitors and for studying filament formation under high enzyme concentrations. They also help identify isoform-specific effects.
How EDITGENE Supports CTP synthase activity Research
Researchers studying CTP synthase activity-related genes often need to determine whether a candidate gene is causally involved in CTP production, filament assembly, or disease phenotypes. EDITGENE provides a comprehensive suite of CRISPR-based services to generate precisely engineered cell models, enabling rigorous functional validation of genes in the CTP synthase pathway.
Contact EDITGENE today to design your custom CRISPR model for CTP synthase activity research.
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| CTPS2 Knockout HEK293 Cell Line | EDJ-KQ13050 | Human | 56474 | Details Get a Quote |
| CTPS2 Knockout A-549 Cell Line | EDJ-KQ42322 | Human | 56474 | Details Get a Quote |
| CTPS2 Knockout HCT 116 Cell Line | EDJ-KQ42323 | Human | 56474 | Details Get a Quote |
| CTPS2 Knockout HeLa Cell Line | EDJ-KQ42324 | Human | 56474 | Details Get a Quote |
Displaying Records 1 To 4 Of 4 Records
Frequently Asked Questions About CTP synthase activity
What is CTP synthase activity?
CTP synthase activity (GO:0003883) is the enzymatic function that converts UTP and glutamine to CTP and glutamate using ATP, as defined by QuickGO.
What genes are involved in CTP synthase activity?
In humans, CTPS1 and CTPS2 encode CTP synthase enzymes; in bacteria, pyrG encodes the enzyme.
What is the reaction catalyzed by CTP synthase?
The reaction is ATP + UTP + glutamine + H2O = ADP + phosphate + CTP + glutamate.
What are cytoophidia?
Cytoophidia are filamentous structures formed by polymerized CTP synthase, observed in bacteria, yeast, Drosophila, and human cells.
How is CTP synthase activity regulated?
It is regulated by feedback inhibition by CTP, interaction between CTPS1 and CTPS2, and filament assembly.
What diseases are linked to CTP synthase activity?
CTPS1 mutations cause severe immunodeficiency, and altered activity is implicated in cancer and bacterial infections.
How can I study CTP synthase activity in the lab?
Enzymatic assays, fluorescence imaging of cytoophidia, metabolomics, and CRISPR screens are common methods.
What is the role of CTPS2?
CTPS2 regulates CTP synthetase activity by interacting with CTPS1, modulating CTP production.
Is CTP synthase a drug target?
Yes, it is a target in cancer and bacterial infections; crizotinib inhibits bacterial PyrG.
How can CRISPR help study CTP synthase?
CRISPR knockout, point mutation, knock-in, and overexpression models allow precise dissection of CTP synthase function in cells.
Conclusion
CTP synthase activity (GO:0003883) is a central enzymatic function in pyrimidine metabolism, essential for CTP production and cellular proliferation. Its dual nature as a soluble enzyme and a filament-forming polymer has made it a fascinating subject of study across species, from bacteria to humans. The involvement of CTPS1 and CTPS2 in immunodeficiency, cancer, and bacterial growth underscores its therapeutic relevance. Advances in structural biology and CRISPR-based models continue to reveal how this enzyme is regulated and how it can be targeted. Researchers equipped with precise genetic tools will be able to further unravel the roles of CTP synthase in health and disease.
References
- 1. Guo CJ et al.. 2024. Structural Basis of Bifunctional CTP/dCTP Synthase.. J Mol Biol 436(20):168750 PMID: 39173734
- 2. Noree C et al.. 2014. Common regulatory control of CTP synthase enzyme activity and filament formation.. Mol Biol Cell 25(15):2282-90 PMID: 24920825
- 3. Thangadurai S et al.. 2022. CTP synthase: the hissing of the cellular serpent.. Histochem Cell Biol 158(6):517-534 PMID: 35881195
- 4. Minet N et al.. 2025. CTPS2 regulates CTP synthetase activity by interacting with CTPS1.. Life Sci Alliance 8(11) PMID: 40957650
- 5. Zhou Y et al.. 2022. Connecting Ras and CTP synthase in Drosophila.. Exp Cell Res 416(1):113155 PMID: 35427600
- 6. Huang Y et al.. 2017. Critical roles of CTP synthase N-terminal in cytoophidium assembly.. Exp Cell Res 354(2):122-133 PMID: 28342900
- 7. Zheng YD et al.. 2022. Crizotinib Shows Antibacterial Activity against Gram-Positive Bacteria by Reducing ATP Production and Targeting the CTP Synthase PyrG.. Microbiol Spectr 10(3):e0088422 PMID: 35674439
- 8. Guo CJ et al.. 2025. Filamentation of hCTPS1 with CTP.. Cell Biosci 15(1):112 PMID: 40739251
