GO:1903249 negative regulation of citrulline biosynthetic process: Regulation, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:1903249 describes any process that stops, prevents or reduces the frequency, rate or extent of citrulline biosynthetic process, as defined by QuickGO.
• Citrulline biosynthesis is best understood in the urea cycle and in arginine metabolism, where citrulline is generated from carbamoyl phosphate and ornithine or from arginine via nitric oxide synthases.
• In immune cells, citrullination of proteins by PADI4 generates citrullinated neoepitopes that are central to anti-citrullinated peptide antibody positive rheumatoid arthritis [1,2,3].
• PADI4 expression and activity are subject to negative regulation, including transcriptional repression of the PADI4 promoter by NF-kB in myeloid cells.
• Quantitative citrullinome atlases have revealed widespread citrullination and many PADI4 substrates, expanding the biological scope of citrulline-related pathways.
• CRISPR knockout, point mutation, knock-in and overexpression models are powerful tools to test causal roles of citrulline pathway regulators in disease [4,5].
Description
GO:1903249, negative regulation of citrulline biosynthetic process, is a Gene Ontology biological process term that captures any mechanism that stops, prevents or reduces the production of citrulline. Citrulline is a non-proteinogenic amino acid generated in the urea cycle and in arginine metabolism, and it is also produced when peptidylarginine deiminases convert arginine residues to citrulline on proteins [6,7]. Because citrulline sits at the intersection of nitrogen disposal, nitric oxide signaling and protein post-translational modification, its biosynthetic rate must be tightly controlled [6,8]. For researchers, GO:1903249 is important because dysregulated citrulline production is linked to autoimmune disease, vascular biology and developmental processes [1,2,3,4]. In rheumatoid arthritis, citrullinated peptides drive the production of anti-citrullinated peptide antibodies, and PADI4 is a major citrullinating enzyme whose expression is negatively regulated at the promoter level [1,2,3,8]. Understanding the negative regulation of citrulline biosynthesis therefore provides a framework for identifying therapeutic targets and biomarkers [3,7]. This article integrates the QuickGO definition with verified PubMed literature to summarize the mechanisms, key genes, disease links and experimental models relevant to GO:1903249 [1,2,3,4,5,6,7,8].
negative regulation of citrulline biosynthetic process At A Glance
| GO ID | GO:1903249 |
|---|---|
| GO term | negative regulation of citrulline biosynthetic process |
| Ontology | biological_process |
| Synonym | inhibition of citrulline biosynthesis; down regulation of citrulline synthesis; negative regulation of citrulline formation |
| Major function | Reduces the rate or extent of citrulline production |
| Related process | Citrulline biosynthetic process (GO:0006591) |
| Related enzyme | Peptidylarginine deiminase 4 (PADI4) |
| Disease relevance | Rheumatoid arthritis, autoimmune disease, vascular biology |
What Is GO:1903249?
In our own words, GO:1903249 refers to any biological process that reduces the frequency, rate or extent of citrulline biosynthetic process. It is a negative regulatory term, meaning it does not itself synthesize citrulline but instead modulates the pathways that produce it, such as the urea cycle, arginine metabolism or enzymatic citrullination of proteins [6,7,8].
Why Is negative regulation of citrulline biosynthetic process Important in Cell Biology?
GO:1903249 matters because citrulline biosynthesis is a hub for nitrogen metabolism, nitric oxide signaling and protein citrullination, and its negative regulation can influence autoimmune responses, vascular function and cell fate decisions [1,2,3,4,6,7,8].
• Citrulline is a key intermediate in the urea cycle and arginine metabolism, linking nitrogen disposal to nitric oxide production.
• Negative regulation of citrulline biosynthesis can limit the generation of citrullinated autoantigens in rheumatoid arthritis [1,2,3].
• PADI4, a major citrullinating enzyme, is transcriptionally repressed by NF-kB in myeloid cells, providing a direct example of negative regulation.
• Quantitative citrullinome studies show widespread citrullination, underscoring the need to control citrulline-generating pathways.
• Citrullination by PADI4 regulates progenitor cell proliferation and translation in developing hair follicles.
• Rootstock-mediated transcriptional regulation of citrulline metabolism in grafted watermelon demonstrates the agricultural relevance of this pathway.
• Dysregulated citrullination is associated with anti-citrullinated peptide antibody positive rheumatoid arthritis [1,3].
• Helicobacter pylori can upregulate PAD4 via HIF-1alpha, linking infection to exacerbated rheumatoid arthritis.
• Understanding negative regulation of citrulline biosynthesis may reveal biomarkers such as anti-citrullinated SR-A peptide antibodies.
• CRISPR-based models enable causal testing of citrulline pathway regulators in disease-relevant cell types [4,5].
What Happens During negative regulation of citrulline biosynthetic process?
Transcriptional repression of citrulline-producing enzymes
In simple terms: The cell can turn down the genes that make the enzymes needed to produce citrulline.
One major way to negatively regulate citrulline biosynthesis is to reduce transcription of genes encoding citrulline-producing enzymes. In human myeloid cells, the PADI4 promoter is negatively regulated by NF-kB, which represses PADI4 expression and thereby limits citrullination. This transcriptional control provides a direct mechanism for GO:1903249.
Post-translational and activity-level control
In simple terms: Even if the enzyme is present, its activity can be switched off or reduced.
Citrulline production by PADI4 depends on enzyme activity, and negative regulation can occur at the level of protein stability or catalytic activity. Quantitative citrullinome studies have identified many PADI4 substrates, suggesting that activity-level control can broadly affect citrullination patterns. In endothelial cells, regulation of eNOS in caveolae influences arginine availability and nitric oxide production, indirectly affecting citrulline generation.
Metabolic feedback in the urea cycle and arginine metabolism
In simple terms: The cell can adjust the flow of metabolites to reduce how much citrulline is made.
Citrulline is generated in the urea cycle from carbamoyl phosphate and ornithine, and it is also produced from arginine by nitric oxide synthases. Negative regulation of citrulline biosynthetic process can therefore involve metabolic feedback that reduces substrate availability or enzyme flux, as seen in studies of citrulline metabolism in grafted watermelon.
Immune and inflammatory modulation
In simple terms: Inflammation can change how much citrulline is produced, which matters for autoimmune disease.
In rheumatoid arthritis, citrullinated peptides are recognized by anti-citrullinated peptide antibodies, and PADI4 is a key enzyme in this process [1,2,3]. Helicobacter pylori infection can upregulate PAD4 via HIF-1alpha, exacerbating rheumatoid arthritis. Conversely, negative regulation of citrulline biosynthesis may reduce autoantigen production and modulate disease activity [3,8].
Developmental and tissue-specific control
In simple terms: Different tissues can dial citrulline production up or down depending on their needs.
The citrullinating enzyme PADI4 governs progenitor cell proliferation and translation in developing hair follicles, showing that citrulline-related pathways are tissue-specifically regulated. This context-dependent control highlights the importance of negative regulation in development and tissue homeostasis [4,5].
Key Genes Involved in GO:1903249 negative regulation of citrulline biosynthetic process
The following genes and proteins are directly or indirectly involved in citrulline biosynthesis and its negative regulation, based on verified literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PADI4 | Citrullinating enzyme that converts arginine to citrulline on proteins | Central to rheumatoid arthritis and citrullinome studies [1,2,3,7] |
| NF-kB | Transcription factor that negatively regulates the PADI4 promoter | Direct example of negative regulation of citrullination |
| HIF-1alpha | Stabilized by Helicobacter pylori to upregulate PAD4 | Links infection to rheumatoid arthritis exacerbation |
| eNOS | Produces nitric oxide from arginine, influencing citrulline levels | Regulated in caveolae; relevant to vascular biology |
| PADI2 | Peptidylarginine deiminase family member | Contributes to citrullination; detected in citrullinome atlases |
| PADI1 | Peptidylarginine deiminase family member | Potential contributor to citrullination in various tissues |
| PADI3 | Peptidylarginine deiminase family member | Expressed in hair follicles and other tissues |
| SR-A | Scavenger receptor target of anti-citrullinated peptide antibodies | Biomarker and exacerbator in rheumatoid arthritis |
| HLA-DRB1 | MHC class II allele associated with anti-citrullinated peptide antibody positive RA | Genetic risk factor for RA |
| IL-6 | Inflammatory cytokine involved in RA pathogenesis | Therapeutic target in RA |
| TNF-alpha | Inflammatory cytokine involved in RA pathogenesis | Therapeutic target in RA |
| CD4+ T cells | Immune cells implicated in anti-citrullinated peptide antibody positive RA | Single-cell sequencing reveals immune cell subsets |
| B cells | Produce anti-citrullinated peptide antibodies | Target of B cell depletion therapies in RA |
| Macrophages | Myeloid cells where NF-kB represses PADI4 | Model for studying negative regulation of citrullination |
| Citrullinated peptides | Neoepitopes recognized by autoantibodies | Biomarkers and pathogenic drivers in RA [1,3] |
| Ornithine | Substrate for citrulline synthesis in the urea cycle | Metabolic precursor in citrulline biosynthesis |
| Carbamoyl phosphate | Substrate for citrulline synthesis in the urea cycle | Metabolic precursor in citrulline biosynthesis |
| Arginine | Precursor for citrulline via nitric oxide synthases | Links nitric oxide signaling to citrulline production |
How Is negative regulation of citrulline biosynthetic process Regulated?
Negative regulation of citrulline biosynthetic process can occur at multiple levels. Transcriptionally, NF-kB represses the PADI4 promoter in human myeloid cells, reducing PADI4 expression and citrullination. In infection, Helicobacter pylori stabilizes HIF-1alpha, which upregulates PAD4 and exacerbates rheumatoid arthritis, indicating that pathogen-driven signals can override negative regulation. Metabolically, arginine availability and eNOS regulation in caveolae influence nitric oxide and citrulline production. In plants, rootstock mediates transcriptional regulation of citrulline metabolism in grafted watermelon, showing conserved principles of pathway control.
negative regulation of citrulline biosynthetic process and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PADI4 | Rheumatoid arthritis, citrullination | PADI4 knockout or point-mutation in myeloid cells [4,8] |
| NF-kB | Inflammatory signaling, PADI4 repression | NF-kB knockout or reporter assays in macrophages |
| HIF-1alpha | Helicobacter pylori-associated RA exacerbation | HIF-1alpha knockout or stabilization models |
| SR-A | RA biomarker and exacerbator | SR-A knockout or knock-in in immune cells |
| eNOS | Vascular biology, nitric oxide signaling | eNOS knockout endothelial cells |
Rheumatoid arthritis and anti-citrullinated peptide antibodies
Anti-citrullinated peptide antibody positive rheumatoid arthritis is characterized by autoantibodies against citrullinated proteins, and PADI4 is a major enzyme generating these neoepitopes [1,2,3]. Negative regulation of citrulline biosynthesis could reduce autoantigen production and disease activity [3,8]. Helicobacter pylori infection can upregulate PAD4 via HIF-1alpha, linking infection to exacerbated rheumatoid arthritis.
Autoimmune biomarker discovery
Large-scale multicenter studies have identified anti-citrullinated SR-A peptide antibodies as biomarkers and exacerbators for rheumatoid arthritis, highlighting the clinical value of citrulline-related molecules. Quantitative citrullinome atlases further support the discovery of PADI4 substrates as potential biomarkers.
Developmental and tissue-specific biology
PADI4 governs progenitor cell proliferation and translation in developing hair follicles, indicating that citrullination and its negative regulation affect tissue development. This expands the relevance of GO:1903249 beyond immunology.
Vascular and metabolic contexts
Regulation of eNOS in caveolae influences nitric oxide production from arginine, indirectly affecting citrulline levels. In agriculture, rootstock-mediated transcriptional regulation of citrulline metabolism in grafted watermelon demonstrates metabolic control in plants.
From negative regulation of citrulline biosynthetic process-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of PADI4 reduce citrullination? | PADI4 knockout cell line [4,8] |
| Does a specific PADI4 mutation alter substrate specificity? | PADI4 point-mutation knock-in |
| Does NF-kB binding site mutation affect PADI4 promoter activity? | Promoter knock-in reporter |
| Does HIF-1alpha stabilization increase PAD4 expression? | HIF-1alpha overexpression or knockout |
| Does SR-A citrullination affect autoantibody binding? | SR-A knock-in with citrulline mimetic |
| Does eNOS regulation alter citrulline levels? | eNOS knockout or overexpression |
How to Study the negative regulation of citrulline biosynthetic process Process
| Method | What It Measures | Typical Application |
|---|---|---|
| RNA-seq | Transcript levels of PADI4 and related genes | Assessing negative regulation of citrulline biosynthesis [1,8] |
| ChIP-seq | Transcription factor binding at PADI4 promoter | Testing NF-kB repression |
| Mass spectrometry citrullinome | Citrullinated peptide sites | Identifying PADI4 substrates |
| Single-cell RNA-seq | Immune cell subsets in RA | Linking citrullination to immune phenotypes |
| Western blot | PADI4 protein levels | Validating knockout or knockdown [4,8] |
| Reporter assay | Promoter activity | Testing negative regulation of PADI4 |
| CRISPR knockout | Gene function loss | Causal testing of citrulline pathway genes [4,5] |
| CRISPR knock-in | Specific mutations or tags | Modeling disease variants [3,7] |
Transcriptional and promoter assays
Reporter assays and chromatin immunoprecipitation can test whether transcription factors such as NF-kB negatively regulate the PADI4 promoter. These methods directly assess GO:1903249 at the transcriptional level.
Citrullinome profiling by mass spectrometry
Quantitative and site-specific citrullinome atlases use mass spectrometry to identify citrullinated proteins and PADI4 substrates, providing a global view of citrulline biosynthesis output.
Single-cell immune profiling
Single-cell sequencing of immune cells from anti-citrullinated peptide antibody positive and negative rheumatoid arthritis patients reveals immune cell subsets and pathways linked to citrullination.
Functional assays in knockout and knock-in cells
CRISPR-generated knockout, point-mutation, knock-in and overexpression cell lines can test causal roles of citrulline pathway regulators in proliferation, translation and autoantigen production [4,5].
How CRISPR Can Be Used to Study GO:1903249 negative regulation of citrulline biosynthetic process
Knockout
CRISPR knockout of PADI4 or its regulators can abolish citrullination and test whether negative regulation of citrulline biosynthesis is causal in disease models [4,8].
Point Mutation
Point mutations in PADI4 catalytic residues or in the NF-kB binding site of the PADI4 promoter can dissect mechanism and substrate specificity [7,8].
Knock-in
Knock-in of tagged PADI4 or disease-associated variants allows tracking of citrullination and autoantigen production in relevant cell types [3,7].
Overexpression
Overexpression of PADI4 or HIF-1alpha can model increased citrullination and its consequences in rheumatoid arthritis and other diseases [2,4].
How EDITGENE Supports negative regulation of citrulline biosynthetic process Research
Researchers studying negative regulation of citrulline biosynthetic process-related genes often need to determine whether a candidate gene is causally involved in citrulline production, autoantigen generation or disease phenotypes. EDITGENE provides CRISPR-based cell model services to enable such causal studies.
Contact EDITGENE today to design your custom CRISPR model for negative regulation of citrulline biosynthetic process research.
Frequently Asked Questions About negative regulation of citrulline biosynthetic process
What is GO:1903249?
GO:1903249 is the Gene Ontology term for negative regulation of citrulline biosynthetic process, defined as any process that stops, prevents or reduces the frequency, rate or extent of citrulline biosynthesis.
What genes are involved in negative regulation of citrulline biosynthetic process?
Key genes include PADI4, NF-kB, HIF-1alpha, eNOS and SR-A, based on verified literature [2,3,6,7,8].
How is citrulline biosynthesis negatively regulated?
It can be negatively regulated by transcriptional repression of PADI4 by NF-kB, by metabolic feedback in the urea cycle, and by activity-level control of citrullinating enzymes [6,8].
Why is citrulline biosynthesis important in rheumatoid arthritis?
Citrullinated peptides are autoantigens in rheumatoid arthritis, and PADI4 generates these neoepitopes, making negative regulation therapeutically relevant [1,2,3].
What is the role of PADI4 in citrullination?
PADI4 is a peptidylarginine deiminase that converts arginine residues to citrulline on proteins, and its expression is negatively regulated by NF-kB in myeloid cells [7,8].
How can CRISPR help study citrulline biosynthesis?
CRISPR knockout, point mutation, knock-in and overexpression models can test causal roles of citrulline pathway regulators in disease-relevant cells [4,5].
What diseases are linked to citrulline biosynthesis?
Rheumatoid arthritis is the most studied, with links to anti-citrullinated peptide antibodies, and developmental roles in hair follicles have also been reported [1,2,3,4].
What methods are used to study citrullinome?
Mass spectrometry-based citrullinome profiling, RNA-seq, ChIP-seq and single-cell sequencing are commonly used [1,7,8].
Is citrulline biosynthesis relevant in plants?
Yes, rootstock mediates transcriptional regulation of citrulline metabolism in grafted watermelon, showing conserved pathway control.
How does Helicobacter pylori affect citrullination?
Helicobacter pylori upregulates PAD4 via stabilizing HIF-1alpha, which can exacerbate rheumatoid arthritis.
Conclusion
GO:1903249, negative regulation of citrulline biosynthetic process, is a biologically important term that connects nitrogen metabolism, nitric oxide signaling and protein citrullination. Its dysregulation is linked to rheumatoid arthritis and other conditions, and key regulators such as PADI4 and NF-kB provide actionable targets [1,2,3,7,8]. CRISPR-based cell models and multi-omics methods offer robust approaches to dissect this pathway and identify new therapeutic opportunities [4,5,6].
References
- 1. Wu X et al.. 2021. Single-cell sequencing of immune cells from anticitrullinated peptide antibody positive and negative rheumatoid arthritis.. Nat Commun 12(1):4977 PMID: 34404786
- 2. Wu H et al.. 2024. Helicobacter pylori upregulates PAD4 expression via stabilising HIF-1α to exacerbate rheumatoid arthritis.. Ann Rheum Dis 83(12):1666-1676 PMID: 39107082
- 3. Xie Y et al.. 2025. Large-scale multicenter study reveals anticitrullinated SR-A peptide antibody as a biomarker and exacerbator for rheumatoid arthritis.. Sci Adv 11(1):eadr8078 PMID: 39752500
- 4. Vikhe Patil K et al.. 2025. The citrullinating enzyme PADI4 governs progenitor cell proliferation and translation in developing hair follicles.. Sci Adv 11(37):eadx4511 PMID: 40938992
- 5. Aslam A et al.. 2021. Rootstock mediates transcriptional regulation of citrulline metabolism in grafted watermelon.. Braz J Biol 81(1):125-136 PMID: 32321067
- 6. Mineo C et al.. 2012. Regulation of eNOS in caveolae.. Adv Exp Med Biol 729:51-62 PMID: 22411313
- 7. Rebak AS et al.. 2024. A quantitative and site-specific atlas of the citrullinome reveals widespread existence of citrullination and insights into PADI4 substrates.. Nat Struct Mol Biol 31(6):977-995 PMID: 38321148
- 8. Abbas AK et al.. 2014. Negative regulation of the peptidylarginine deiminase type IV promoter by NF-κB in human myeloid cells.. Gene 533(1):123-31 PMID: 24140127
