GO:0019805 quinolinate biosynthetic process: NAD+ Precursor Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0019805 quinolinate biosynthetic process describes the enzymatic steps that produce quinolinate, the anion of quinolinic acid (2,3-pyridinedicarboxylic acid).
• Quinolinate is a key intermediate in de novo NAD+ biosynthesis and is generated from tryptophan via the kynurenine pathway.
• The pathway is conserved from bacteria to humans and is essential for cellular NAD+ supply, especially in kidney and immune cells.
• Dysregulation of quinolinate production is linked to inflammatory bowel disease, acute kidney injury, and neuroinflammatory conditions.
• Quinolinate can act as a neurotoxin and an immune modulator, interacting with receptors such as RAGE.
• Research on this process uses knockout, knock-in, and overexpression cell models, combined with metabolomics and CRISPR screening.
Description
Quinolinate biosynthetic process (GO:0019805) is the set of chemical reactions and pathways that result in the formation of quinolinate, the anion of quinolinic acid (2,3-pyridinedicarboxylic acid). This process is a central segment of the de novo NAD+ biosynthetic pathway, which converts tryptophan into nicotinamide adenine dinucleotide (NAD+). In eukaryotes, quinolinate is produced in the cytosol and then used by quinolinate phosphoribosyltransferase to form nicotinate mononucleotide, a direct precursor of NAD+. The pathway is essential for maintaining NAD+ levels in tissues such as the kidney and immune system, and its dysfunction has been implicated in human disease. Researchers study quinolinate biosynthesis because it sits at the intersection of amino acid catabolism, redox balance, and immune regulation. The kynurenine pathway, which includes quinolinate synthesis, is the major route of tryptophan degradation, and its intermediates influence inflammation, neurotoxicity, and cell survival. For example, increased tryptophan metabolism and quinolinate production are associated with active inflammatory bowel diseases, and impaired de novo NAD+ biosynthesis, including quinolinate pathway enzymes, is observed in acute kidney injury. In the brain, quinolinate acts as an excitotoxin and can activate the receptor for advanced glycation end products (RAGE), contributing to early neuropathological processes. Understanding GO:0019805 therefore requires integrating enzymology, metabolic flux, and disease context. The pathway is amenable to genetic manipulation using CRISPR-based knockout, point mutation, knock-in, and overexpression strategies, which allow researchers to dissect the contribution of individual enzymes to quinolinate levels and downstream NAD+ production. This article provides a research-grade overview of the quinolinate biosynthetic process, its key genes, regulatory features, disease relevance, and experimental models for studying it.
quinolinate biosynthetic process At A Glance
| GO ID | GO:0019805 |
|---|---|
| GO term | quinolinate biosynthetic process |
| Ontology | biological_process |
| Synonym | quinolinate anabolism, quinolinate biosynthesis, quinolinate formation, quinolinate synthesis |
| Definition | The chemical reactions and pathways resulting in the formation of quinolinate, the anion of quinolinic acid, also known as 2,3-pyridinedicarboxylic acid. |
| Major function | Production of quinolinate as a precursor for de novo NAD+ biosynthesis and as a signaling/neuroactive metabolite. |
| Pathway context | Kynurenine pathway of tryptophan degradation; de novo NAD+ biosynthesis. |
| Key enzyme | 3-hydroxyanthranilate 3,4-dioxygenase (HAAO) catalyzes the formation of quinolinate from 3-hydroxyanthranilate. |
| Subcellular location | Cytosol (in eukaryotes). |
| Related disease | Inflammatory bowel disease, acute kidney injury, neurodegenerative conditions. |
What Is GO:0019805?
The quinolinate biosynthetic process (GO:0019805) is defined as the chemical reactions and pathways resulting in the formation of quinolinate, the anion of quinolinic acid, also known as 2,3-pyridinedicarboxylic acid. In practice, this term covers the enzymatic conversion of tryptophan-derived intermediates, such as 3-hydroxyanthranilate, into quinolinate, a step catalyzed by 3-hydroxyanthranilate 3,4-dioxygenase (HAAO) in the kynurenine pathway. Quinolinate is not an end product; it is a precursor for NAD+ and is further metabolized by quinolinate phosphoribosyltransferase (QPRT) to nicotinate mononucleotide. Thus, GO:0019805 describes a biosynthetic segment of the larger de novo NAD+ pathway, with quinolinate as the immediate product.
Why Is quinolinate biosynthetic process Important in Cell Biology?
The quinolinate biosynthetic process is important because it is a mandatory step in the de novo NAD+ pathway, which supports cellular energy metabolism, DNA repair, and redox homeostasis. Quinolinate itself is a neuroactive and immunomodulatory metabolite; when produced in excess, it can contribute to excitotoxicity and neuroinflammation through mechanisms involving RAGE and other targets. Clinically, altered quinolinate pathway activity has been observed in inflammatory bowel diseases, acute kidney injury, and major depressive disorder, making it a candidate biomarker and therapeutic target. Studying GO:0019805 helps researchers understand how tryptophan metabolism is rerouted during inflammation and how NAD+ depletion contributes to tissue injury.
• Quinolinate is an essential intermediate in de novo NAD+ biosynthesis, linking tryptophan catabolism to cellular energy metabolism.
• The pathway is conserved across species, allowing the use of model organisms and cell lines to study human disease mechanisms.
• Increased quinolinate production is associated with active inflammatory bowel diseases, suggesting a role in mucosal inflammation.
• Impaired de novo NAD+ biosynthesis, including quinolinate pathway enzymes, is observed in acute kidney injury in humans.
• Quinolinate acts as an excitotoxin and can interact with RAGE, contributing to early neuropathological processes.
• Kynurenine pathway dysregulation, including quinolinate, is implicated in major depressive disorder and neuroinflammation.
• Quinolinate levels can be measured in saliva and other biofluids, offering non-invasive biomarker potential.
• The pathway is a target for CRISPR-based functional genomics to identify modulators of NAD+ metabolism.
• Understanding quinolinate biosynthesis may inform therapeutic strategies for inflammatory and metabolic diseases.
• Enzymes of this pathway are attractive targets for small-molecule and genetic interventions.
What Happens During quinolinate biosynthetic process?
Tryptophan catabolism to 3-hydroxyanthranilate
In simple terms: Tryptophan is broken down step by step into an intermediate called 3-hydroxyanthranilate.
The quinolinate biosynthetic process begins with the conversion of tryptophan through the kynurenine pathway. Tryptophan is first oxidized to N-formylkynurenine by tryptophan 2,3-dioxygenase (TDO) or indoleamine 2,3-dioxygenase (IDO), then deformylated to kynurenine. Kynurenine is subsequently hydroxylated to 3-hydroxykynurenine and cleaved to 3-hydroxyanthranilate by kynureninase. These upstream steps generate the substrate for the committed quinolinate-forming reaction. In immune and inflammatory contexts, cytokines such as interferon-gamma upregulate IDO, increasing flux through this pathway.
Oxidative cleavage of 3-hydroxyanthranilate to quinolinate
In simple terms: An enzyme called HAAO opens the ring of 3-hydroxyanthranilate to form quinolinate.
The central reaction of GO:0019805 is catalyzed by 3-hydroxyanthranilate 3,4-dioxygenase (HAAO), which uses non-heme Fe(II) to insert molecular oxygen into 3-hydroxyanthranilate, leading to ring opening and spontaneous cyclization to quinolinate. This enzyme is highly conserved and represents the point of no return for quinolinate production. HAAO activity determines the rate of quinolinate formation and is a key node for regulation by substrate availability and metal cofactors. In humans, HAAO deficiency is a rare inborn error of metabolism that affects NAD+ synthesis and neurological function.
Quinolinate as a precursor for NAD+
In simple terms: Quinolinate is then converted into a building block for NAD+, the cell's energy currency.
Once formed, quinolinate is acted upon by quinolinate phosphoribosyltransferase (QPRT), which transfers a phosphoribosyl group from PRPP to quinolinate, yielding nicotinate mononucleotide and releasing CO2. This step commits quinolinate to the NAD+ biosynthetic route. Nicotinate mononucleotide is then adenylylated to nicotinate adenine dinucleotide and amidated to NAD+. Thus, the quinolinate biosynthetic process is tightly coupled to downstream NAD+ production, and its output influences cellular NAD+ pools.
Compartmentalization and tissue-specific roles
In simple terms: The pathway operates in different tissues, with the kidney and immune cells being especially important.
In eukaryotes, the quinolinate biosynthetic enzymes are cytosolic, and the pathway is active in liver, kidney, and immune cells. In the kidney, de novo NAD+ biosynthesis, including quinolinate formation, is critical for tubular cell homeostasis, and its impairment is observed in acute kidney injury. In immune cells, quinolinate production is part of the inflammatory response and can modulate T-cell function. Tissue-specific expression of HAAO and QPRT contributes to differences in flux and quinolinate accumulation.
Regulation by substrate availability and feedback
In simple terms: The pathway speeds up or slows down depending on how much tryptophan is available and the cell's NAD+ needs.
Flux through quinolinate biosynthesis is regulated by the availability of tryptophan and the activity of upstream enzymes such as IDO and TDO, which are induced by inflammatory cytokines. NAD+ levels can feedback on the pathway, although the exact mechanisms in humans are not fully defined. Additionally, HAAO requires Fe(II) and is sensitive to oxidative stress, which can affect its catalytic activity. These regulatory features make quinolinate production responsive to nutritional and inflammatory signals.
Key Genes Involved in GO:0019805 quinolinate biosynthetic process
The following genes and proteins are directly involved in or closely associated with the quinolinate biosynthetic process and its regulation.
| Gene | Major Role | Research Relevance |
|---|---|---|
| HAAO | Catalyzes the formation of quinolinate from 3-hydroxyanthranilate | Core enzyme of GO:0019805; target for knockout and point mutation studies |
| QPRT | Converts quinolinate to nicotinate mononucleotide | Downstream enzyme; knockout alters NAD+ levels |
| IDO1 | Rate-limiting enzyme for tryptophan catabolism to kynurenine | Regulates substrate supply; inflammation-induced |
| IDO2 | Tryptophan catabolic enzyme with immunomodulatory roles | Potential modifier of quinolinate flux |
| TDO2 | Tryptophan 2,3-dioxygenase; liver-specific tryptophan catabolism | Controls systemic tryptophan availability |
| KYNU | Kynureninase; produces 3-hydroxyanthranilate | Upstream of HAAO; affects quinolinate precursor levels |
| KMO | Kynurenine 3-monooxygenase; generates 3-hydroxykynurenine | Regulates pathway flux and neurotoxicity |
| ACMSD | Aminocarboxymuconate semialdehyde decarboxylase; diverts pathway | Competes with quinolinate formation |
| NADSYN1 | NAD+ synthetase; final step of NAD+ biosynthesis | Downstream of quinolinate; affects NAD+ pool |
| NMNAT1 | Nicotinamide mononucleotide adenylyltransferase | NAD+ salvage and biosynthesis |
| SLC7A5 | Amino acid transporter; influences tryptophan uptake | Modulates substrate availability |
| SLC36A4 | Proton-coupled amino acid transporter; tryptophan transport | Potential regulator of pathway flux |
| RAGE | Receptor for advanced glycation end products; binds quinolinate | Mediates neuroinflammatory effects of quinolinate |
| IL1B | Pro-inflammatory cytokine; induces IDO | Links inflammation to quinolinate production |
| IFNG | Interferon gamma; induces IDO and kynurenine pathway | Inflammatory regulator of quinolinate synthesis |
| TNF | Tumor necrosis factor; modulates inflammation and metabolism | Context-dependent regulator |
| NFKB1 | Transcription factor; drives inflammatory gene expression | Indirect regulator of pathway enzymes |
| TP53 | Tumor suppressor; regulates metabolism and NAD+ homeostasis | Potential link to quinolinate pathway in cancer |
How Is quinolinate biosynthetic process Regulated?
The quinolinate biosynthetic process is primarily regulated at the level of substrate supply and enzyme expression. Inflammatory cytokines such as interferon-gamma and interleukin-1 beta induce IDO1, increasing tryptophan catabolism and flux toward quinolinate. TDO2 in the liver controls systemic tryptophan availability and can influence quinolinate production. HAAO activity depends on Fe(II) and is sensitive to oxidative stress, providing a post-translational layer of regulation. NAD+ levels may exert feedback inhibition on the pathway, although the molecular details in humans remain incompletely understood. In disease states such as inflammatory bowel disease and acute kidney injury, pathway activity is altered, reflecting both transcriptional and metabolic regulation.
quinolinate biosynthetic process and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| HAAO | Acute kidney injury; NAD+ depletion | HAAO knockout kidney epithelial cells; point mutation of catalytic residues |
| IDO1 | Inflammatory bowel disease; chronic inflammation | IDO1 overexpression in intestinal organoids; knockout in macrophages |
| QPRT | NAD+ homeostasis; neuroprotection | QPRT knockout neurons; knock-in of patient variants |
| RAGE | Neuroinflammation; Alzheimer's disease | RAGE knockout microglia; quinolinate-treated cultures |
| KYNU | Depression; neurotoxicity | KYNU knockout iPSC-derived neurons; overexpression models |
Quinolinate biosynthesis in inflammatory bowel disease
Increased tryptophan metabolism, including quinolinate production, is associated with activity of inflammatory bowel diseases. In patients with active Crohn's disease and ulcerative colitis, serum and tissue levels of kynurenine pathway metabolites are elevated, suggesting that inflammation drives flux through the quinolinate biosynthetic process. This has implications for mucosal immune regulation and may provide biomarkers for disease activity.
Quinolinate biosynthesis and acute kidney injury
De novo NAD+ biosynthetic impairment, including reduced quinolinate pathway activity, has been observed in acute kidney injury in humans. The kidney relies on this pathway for NAD+ supply, and its dysfunction may contribute to tubular injury and impaired recovery. Targeting the quinolinate biosynthetic process could therefore be a strategy to preserve NAD+ levels in kidney disease.
Quinolinate biosynthesis in neurodegeneration and depression
Quinolinate is a neuroactive metabolite that can act as an excitotoxin and interact with RAGE, contributing to early neuropathological processes. Kynurenine pathway dysregulation, including altered quinolinate levels, has been implicated in Alzheimer's disease and major depressive disorder, where excitotoxicity, neuroinflammation, and oxidative stress converge. Modulating quinolinate production may offer therapeutic avenues for these conditions.
Quinolinate biosynthesis in Sjögren's disease
Salivary kynurenine pathway metabolites, including quinolinate, have been proposed as non-invasive markers of glandular dysfunction in Sjögren's disease. This suggests that the quinolinate biosynthetic process is active in salivary glands and may reflect systemic inflammatory status. Further studies are needed to validate these findings and understand the underlying mechanisms.
From quinolinate biosynthetic process-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does HAAO loss reduce quinolinate and NAD+ levels? | HAAO knockout cell lines (e.g., HEK293, renal epithelial cells) |
| How do point mutations in HAAO affect enzyme activity? | HAAO point-mutation knock-in cells using CRISPR |
| Can overexpression of IDO1 increase quinolinate flux? | IDO1 overexpression in immune or epithelial cells |
| What is the role of QPRT in NAD+ maintenance? | QPRT knockout and tagged knock-in for localization |
| Does quinolinate mediate neurotoxicity via RAGE? | RAGE knockout neurons treated with quinolinate |
| Can CRISPR screening identify modifiers of quinolinate levels? | Genome-wide CRISPR knockout library in reporter cells |
How to Study the quinolinate biosynthetic process Process
| Method | What It Measures | Typical Application |
|---|---|---|
| LC-MS/MS metabolomics | Quinolinate and pathway intermediate levels | Quantifying pathway activity in cells and biofluids |
| Stable isotope tracing | Flux through the kynurenine pathway | Determining de novo NAD+ synthesis rates |
| CRISPR knockout screening | Genes affecting quinolinate/NAD+ levels | Discovery of novel regulators |
| RNA-seq | Expression of pathway enzymes | Assessing transcriptional regulation by inflammation |
| Proteomics | Protein abundance and modifications | Validating enzyme expression changes |
| NAD+ reporter assays | Intracellular NAD+ levels | Live-cell monitoring of pathway output |
| Immunofluorescence | Subcellular localization of enzymes | Studying compartmentalization |
| Enzyme activity assays | HAAO or QPRT catalytic activity | Functional validation of mutations |
Metabolomics and flux analysis
Targeted metabolomics using LC-MS/MS can quantify quinolinate and other kynurenine pathway intermediates in cells and biofluids. Stable isotope tracing with labeled tryptophan allows flux analysis through the quinolinate biosynthetic process. These methods are essential for validating genetic models and assessing pathway activity in disease.
CRISPR-based functional genomics
Genome-wide CRISPR knockout screens can identify genes that regulate quinolinate levels or NAD+ homeostasis. Focused libraries targeting metabolic enzymes can dissect the pathway with high resolution. Coupling screens with metabolomic readouts enables discovery of novel regulators.
Transcriptomics and proteomics
RNA-seq can reveal expression changes in HAAO, QPRT, IDO1, and other pathway genes under inflammatory or metabolic stress. Proteomics can quantify enzyme abundance and post-translational modifications. These approaches help link pathway activity to cellular states.
Imaging and reporter assays
Fluorescent or luminescent reporters for NAD+ or quinolinate can be used in live cells to monitor pathway activity. Immunofluorescence can localize pathway enzymes and assess subcellular distribution. These methods complement biochemical assays.
How CRISPR Can Be Used to Study GO:0019805 quinolinate biosynthetic process
Knockout
CRISPR knockout of HAAO or QPRT can abolish quinolinate production or its downstream conversion, respectively, allowing researchers to test the consequences for NAD+ levels and cell survival. Knockout of IDO1 or TDO2 reduces upstream flux, providing complementary models. These models are valuable for validating pathway dependencies in disease contexts.
Point Mutation
Introducing point mutations in HAAO catalytic residues or regulatory sites can dissect enzyme mechanism and identify loss-of-function variants. Point mutations in QPRT can reveal residues critical for substrate binding. Such models are useful for studying rare metabolic disorders.
Knock-in
Knock-in of tagged HAAO or QPRT (e.g., FLAG, GFP) enables localization and interaction studies without altering endogenous regulation. Knock-in of disease-associated variants can model human mutations in isogenic cell lines. This approach is powerful for linking genotype to metabolic phenotype.
Overexpression
Overexpression of IDO1, HAAO, or QPRT can increase flux through the quinolinate biosynthetic process, mimicking inflammatory or metabolic states. Overexpression models are useful for testing inhibitors or activators. They can also reveal dose-dependent effects on NAD+ and cell viability.
How EDITGENE Supports quinolinate biosynthetic process Research
Researchers studying quinolinate biosynthetic process-related genes often need to determine whether a candidate gene is causally involved in pathway regulation, disease progression, or therapeutic response. EDITGENE provides a comprehensive suite of CRISPR-based services to generate precisely engineered cell models for such studies.
Contact EDITGENE today to design your custom CRISPR model for quinolinate biosynthetic process research.
Frequently Asked Questions About quinolinate biosynthetic process
What is quinolinate biosynthetic process?
Quinolinate biosynthetic process (GO:0019805) is the set of enzymatic reactions that produce quinolinate, the anion of quinolinic acid, primarily from tryptophan via the kynurenine pathway.
What genes are involved in quinolinate biosynthetic process?
Key genes include HAAO, QPRT, IDO1, IDO2, TDO2, KYNU, and KMO, which collectively regulate the production and downstream utilization of quinolinate.
What is the role of HAAO in quinolinate biosynthesis?
HAAO (3-hydroxyanthranilate 3,4-dioxygenase) catalyzes the oxidative cleavage of 3-hydroxyanthranilate to form quinolinate, the central step of GO:0019805.
How is quinolinate linked to NAD+?
Quinolinate is a direct precursor for NAD+ biosynthesis; QPRT converts it to nicotinate mononucleotide, which is further metabolized to NAD+.
What diseases are associated with quinolinate biosynthesis?
Altered quinolinate production is associated with inflammatory bowel diseases, acute kidney injury, neurodegenerative conditions, and major depressive disorder.
Can quinolinate be measured in biofluids?
Yes, quinolinate and other kynurenine pathway metabolites can be quantified in serum, urine, and saliva using LC-MS/MS.
What experimental models are used to study quinolinate biosynthesis?
Common models include CRISPR knockout and overexpression cell lines, patient-derived cells, and animal models, combined with metabolomics and flux analysis.
Is quinolinate neurotoxic?
Quinolinate can act as an excitotoxin and interact with RAGE, contributing to neuroinflammation and neurodegeneration.
How does inflammation affect quinolinate production?
Inflammatory cytokines such as interferon-gamma induce IDO1, increasing tryptophan catabolism and flux toward quinolinate.
What is the difference between quinolinate and quinolinic acid?
Quinolinate is the anion of quinolinic acid (2,3-pyridinedicarboxylic acid); the terms are often used interchangeably in the context of the pathway.
Conclusion
The quinolinate biosynthetic process (GO:0019805) is a conserved metabolic pathway that produces quinolinate, a key intermediate in de novo NAD+ biosynthesis and a neuroactive metabolite. Its dysregulation is linked to inflammatory, renal, and neurological diseases, making it a compelling target for research. Advances in CRISPR-based cell modeling and metabolomics now allow precise interrogation of this pathway, from enzyme mechanism to disease relevance. Continued study of quinolinate biosynthesis will likely yield new insights into NAD+ biology and therapeutic opportunities.
References
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