GO:0004588 orotate phosphoribosyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004588 describes the molecular function of orotate phosphoribosyltransferase (OPRT), which catalyzes the reversible conversion of orotate to orotidine 5'-monophosphate (OMP) using 5-phospho-alpha-D-ribose 1-diphosphate (PRPP).
• OPRT is a core enzyme of the de novo pyrimidine biosynthesis pathway, and its activity is essential for producing UMP, the precursor of all pyrimidine nucleotides.
• In some organisms, OPRT is fused to orotidine 5'-monophosphate decarboxylase (OMPDC) as a bifunctional enzyme, as seen in Plasmodium falciparum.
• Altered OPRT activity has been linked to cancer prognosis, including renal cell carcinoma and bladder carcinoma, where higher activity correlates with worse outcomes.
• Decreased OPRT activity can produce resistance to 5-fluorouracil (5-FU) in gastric cancer cells, making it a potential biomarker for chemotherapy response.
• OPRT is overexpressed in malignant pleural mesothelioma, and high expression may predict dramatic response to certain therapies.
Description
Orotate phosphoribosyltransferase (OPRT) activity, encoded by GO:0004588, is a molecular function that catalyzes the transfer of a phosphoribosyl group from PRPP to orotate, yielding OMP and pyrophosphate. This reaction is a critical step in the de novo pyrimidine biosynthesis pathway, which supplies the pyrimidine nucleotides required for RNA and DNA synthesis. Because pyrimidines are essential for cell proliferation, OPRT activity is tightly linked to growth and division, making it a subject of intense research in cancer biology and chemotherapy. The enzyme has been studied across species, from yeast to humans, and its kinetic properties, structural stability, and regulatory roles have been characterized. In recent years, OPRT has gained attention as a prognostic marker in several malignancies, including renal cell carcinoma, bladder carcinoma, and malignant pleural mesothelioma. Furthermore, its activity influences the efficacy of antimetabolite drugs such as 5-fluorouracil, as reduced OPRT levels can lead to drug resistance. Understanding OPRT function at the molecular level is therefore crucial for developing targeted therapies and improving patient outcomes.
orotate phosphoribosyltransferase activity At A Glance
| GO ID | GO:0004588 |
|---|---|
| GO term | orotate phosphoribosyltransferase activity |
| Ontology | molecular_function |
| Synonym | OPRT activity; OPRTase activity; orotate phosphoribosyl pyrophosphate transferase activity; orotic acid phosphoribosyltransferase activity; orotidine 5'-monophosphate pyrophosphorylase activity; orotidine-5'-phosphate:diphosphate phospho-alpha-D-ribosyl-transferase activity; orotidine-5'-phosphate diphosphorylase activity; orotidine-5'-phosphate pyrophosphorylase activity; orotidine monophosphate pyrophosphorylase activity; orotidine phosphoribosyltransferase activity; orotidylate phosphoribosyltransferase activity; orotidylate pyrophosphorylase activity; orotidylic acid phosphorylase activity; orotidylic acid pyrophosphorylase activity; orotidylic phosphorylase activity; orotidylic pyrophosphorylase activity |
| Major function | Catalyzes the conversion of orotate to OMP in de novo pyrimidine biosynthesis |
| Reaction | orotidine 5'-phosphate + diphosphate = orotate + 5-phospho-alpha-D-ribose 1-diphosphate |
| Substrates | Orotate and 5-phospho-alpha-D-ribose 1-diphosphate (PRPP) |
| Products | Orotidine 5'-monophosphate (OMP) and diphosphate (pyrophosphate) |
| Pathway | De novo pyrimidine biosynthesis (UMP synthesis) |
What Is GO:0004588?
GO:0004588 defines the catalytic activity of orotate phosphoribosyltransferase, which mediates the reversible reaction: orotidine 5'-phosphate + diphosphate = orotate + 5-phospho-alpha-D-ribose 1-diphosphate. In the forward direction, the enzyme transfers the 5-phospho-alpha-D-ribose 1-diphosphate (PRPP) moiety to orotate, forming orotidine 5'-monophosphate (OMP) and releasing pyrophosphate. This activity is synonymous with OPRTase, orotate phosphoribosyl pyrophosphate transferase, and several other names reflecting its role in pyrimidine biosynthesis. The reaction is a key step in the de novo synthesis of uridine monophosphate (UMP), which is subsequently converted to other pyrimidine nucleotides.
Why Is orotate phosphoribosyltransferase activity Important in Cell Biology?
OPRT activity is indispensable for de novo pyrimidine biosynthesis, providing the building blocks for RNA and DNA. Its dysregulation has been implicated in cancer progression and chemoresistance, making it a valuable biomarker and potential therapeutic target. Additionally, OPRT is a component of bifunctional enzymes in some pathogens, offering a target for antiparasitic drug development.
• Essential for de novo pyrimidine biosynthesis and nucleotide homeostasis.
• Prognostic marker in renal cell carcinoma: higher OPRT activity correlates with worse survival.
• Prognostic marker in bladder carcinoma: OPRT activity predicts recurrence and progression.
• Mediates sensitivity to 5-fluorouracil (5-FU) in gastric cancer; decreased activity causes resistance.
• Overexpressed in malignant pleural mesothelioma and associated with dramatic treatment response.
• Bifunctional OPRT-OMPDC in Plasmodium falciparum is a potential antimalarial target.
• Thermostability and C-terminal deletions affect enzyme activity, informing protein engineering.
• Fluorometric assays enable rapid measurement of OPRT activity for clinical and research applications.
Molecular Mechanism of orotate phosphoribosyltransferase activity
Substrate Binding and Catalysis
In simple terms: The enzyme grabs two molecules, orotate and PRPP, and joins them together while releasing pyrophosphate.
OPRT catalyzes the transfer of the phosphoribosyl group from PRPP to orotate, forming OMP and pyrophosphate. The reaction proceeds via an ordered bi-bi mechanism where PRPP binds first, followed by orotate, and products are released in the order OMP then pyrophosphate. The enzyme requires divalent cations, such as Mg2+, for optimal activity.
Bifunctional Enzyme Architecture
In simple terms: In some organisms, OPRT is physically linked to another enzyme, OMPDC, forming a two-in-one protein.
In Plasmodium falciparum, OPRT and orotidine 5'-monophosphate decarboxylase (OMPDC) are fused into a single bifunctional polypeptide. This fusion allows efficient channeling of the unstable intermediate OMP from the OPRT active site to the OMPDC active site, enhancing pathway flux.
Structural Determinants of Activity and Stability
In simple terms: The tail end of the OPRT protein affects how well it works and how stable it is at high temperatures.
Studies on Thermus thermophilus OPRT have shown that C-terminal deletions significantly reduce catalytic activity and thermostability, indicating that the C-terminus is important for maintaining the active conformation. This highlights the sensitivity of OPRT function to structural perturbations.
Kinetic Parameters and Assay Development
In simple terms: Scientists have developed a simple fluorescent test to measure how fast OPRT works.
A fluorometric assay for OPRT activity has been developed using a selective fluorogenic reaction for orotic acid, allowing sensitive and rapid quantification of enzyme activity in biological samples. This assay facilitates high-throughput screening and clinical diagnostics.
Key Genes Involved in GO:0004588 orotate phosphoribosyltransferase activity
The following genes and proteins are directly associated with orotate phosphoribosyltransferase activity or its regulation.
| Gene | Major Role | Research Relevance |
|---|---|---|
| UMPS | Encodes a bifunctional enzyme with OPRT and OMPDC activities in humans | Mutations cause orotic aciduria; target for cancer and metabolic studies |
| PYR5,6 | Yeast gene encoding OPRT and OMPDC | Model for studying pyrimidine biosynthesis and enzyme structure |
| pyrE | Bacterial gene encoding OPRT | Target for antibacterial drug discovery |
| pyrF | Bacterial gene encoding OMPDC | Often fused with pyrE in some species |
| Thermus thermophilus pyrE | OPRT from thermophilic bacterium | Model for thermostability and C-terminal function |
| Plasmodium falciparum OPRT | Bifunctional OPRT-OMPDC | Antimalarial drug target |
| Human OPRT | Catalytic domain of UMPS | Prognostic marker in cancers |
| OPRT (renal cell carcinoma) | Enzyme activity measured in tumor tissues | Correlates with prognosis |
| OPRT (bladder carcinoma) | Enzyme activity measured in tumor tissues | Predicts recurrence and progression |
| OPRT (gastric cancer) | Enzyme activity linked to 5-FU sensitivity | Resistance marker |
| OPRT (mesothelioma) | Overexpressed in malignant pleural mesothelioma | Potential therapeutic target |
| PRPP synthetase | Produces PRPP, the substrate for OPRT | Regulates flux through pyrimidine pathway |
| OMPDC | Catalyzes the next step after OPRT | Often fused with OPRT |
| CAD | Multienzyme complex in pyrimidine biosynthesis | Upstream of OPRT |
| Dihydroorotate dehydrogenase | Catalyzes step before OPRT | Potential target for inhibitors |
| UMP synthase | Bifunctional enzyme in humans | Contains OPRT and OMPDC domains |
| CTP synthetase | Converts UTP to CTP | Downstream of OPRT |
How Is orotate phosphoribosyltransferase activity Regulated?
OPRT activity is regulated at multiple levels. In humans, the UMPS gene encodes a bifunctional enzyme with both OPRT and OMPDC activities, and its expression is cell-cycle dependent, peaking during S phase to meet the demand for pyrimidines during DNA replication. Allosteric regulation by nucleotides, such as UTP and CTP, can feedback-inhibit the pathway. Additionally, OPRT activity can be modulated by post-translational modifications, although specific mechanisms remain to be fully elucidated. In cancer cells, OPRT expression and activity are often dysregulated, contributing to altered pyrimidine metabolism and drug resistance.
orotate phosphoribosyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| UMPS | Orotic aciduria (rare metabolic disorder) | Knockout cell lines, patient-derived fibroblasts |
| OPRT (renal cell carcinoma) | Renal cell carcinoma prognosis | Renal cancer cell lines (e.g., 786-O, ACHN) with OPRT knockdown or overexpression |
| OPRT (bladder carcinoma) | Bladder carcinoma progression | Bladder cancer cell lines (e.g., T24, J82) for OPRT activity assays |
| OPRT (gastric cancer) | 5-Fluorouracil resistance | Gastric cancer cell lines (e.g., MKN45, AGS) with OPRT knockout |
| OPRT (mesothelioma) | Malignant pleural mesothelioma | Mesothelioma cell lines (e.g., MSTO-211H) for OPRT overexpression studies |
Orotate phosphoribosyltransferase activity in Cancer Prognosis
In renal cell carcinoma, higher OPRT activity is significantly associated with worse prognosis, including shorter survival and higher recurrence rates. Similarly, in bladder carcinoma, elevated OPRT activity predicts disease progression and poor clinical outcomes. These findings suggest that OPRT activity could serve as a prognostic biomarker and potential therapeutic target in these cancers.
OPRT Activity and Chemoresistance
Decreased OPRT activity has been shown to produce resistance to 5-fluorouracil (5-FU) in a human gastric cancer cell line. Since 5-FU is a common chemotherapeutic agent that requires OPRT for its activation, low OPRT levels can lead to treatment failure. Assessing OPRT activity may help predict patient response to 5-FU-based therapies.
OPRT Overexpression in Malignant Pleural Mesothelioma
OPRT is overexpressed in malignant pleural mesothelioma, and one case with high OPRT expression showed a dramatic response to therapy. This suggests that OPRT expression levels could guide treatment decisions and that targeting OPRT may be beneficial in this aggressive cancer.
From orotate phosphoribosyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does OPRT loss affect pyrimidine biosynthesis and cell proliferation? | UMPS knockout cell lines (e.g., HCT116, HEK293T) |
| Does a specific point mutation in UMPS alter OPRT activity? | Point-mutation knock-in cell lines (e.g., UMPS R263Q) |
| Can we tag endogenous OPRT for live-cell imaging? | Knock-in of fluorescent tag (e.g., GFP) at the UMPS locus |
| Does OPRT overexpression confer 5-FU resistance? | Stable overexpression of UMPS in gastric cancer cells |
| What is the effect of OPRT inhibition on cancer cell growth? | CRISPR knockout or CRISPRi knockdown in cancer cell lines |
| Can we screen for synthetic lethal partners of OPRT? | Genome-wide CRISPR library screening in OPRT-deficient cells |
How to Study the orotate phosphoribosyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Fluorometric assay | OPRT enzymatic activity via orotic acid detection | High-throughput screening, clinical samples |
| Spectrophotometric assay | OMP formation or orotate consumption | Kinetic studies |
| qRT-PCR | UMPS mRNA expression | Cancer prognosis, gene regulation |
| Western blot | OPRT protein levels | Expression analysis in tissues |
| CRISPR-Cas9 knockout | Loss of OPRT function | Phenotypic studies, drug resistance |
| CRISPR knock-in | Tagged or mutant OPRT | Live-cell imaging, structure-function |
| X-ray crystallography | Three-dimensional structure of OPRT | Drug design, mechanism |
| Thermostability assays | Protein stability | Mutant characterization |
Enzymatic Activity Assays
OPRT activity can be measured using a fluorometric assay that selectively detects orotic acid, the product of the reverse reaction. This method is sensitive and suitable for high-throughput screening. Traditional spectrophotometric assays monitoring the conversion of orotate to OMP are also used.
Gene Expression Analysis
Quantitative RT-PCR and RNA-seq can measure UMPS mRNA levels in tissues and cell lines. Immunohistochemistry and Western blotting are used to assess OPRT protein expression, as demonstrated in mesothelioma and carcinoma studies.
CRISPR-Cas9 Genome Editing
CRISPR-Cas9 knockout of UMPS or OPRT domain can create isogenic cell lines to study loss-of-function phenotypes, including pyrimidine auxotrophy and drug sensitivity. Point mutations can be introduced to dissect catalytic residues.
Structural and Biophysical Methods
X-ray crystallography and NMR spectroscopy can resolve the structure of OPRT and its complexes with substrates and inhibitors. Thermostability assays, such as circular dichroism, are used to study mutant enzymes.
How CRISPR Can Be Used to Study GO:0004588 orotate phosphoribosyltransferase activity
Knockout
CRISPR-Cas9 knockout of the UMPS gene or the OPRT domain can generate cell lines completely lacking OPRT activity. These models are useful for studying pyrimidine auxotrophy, drug resistance, and synthetic lethality. For example, knocking out OPRT in gastric cancer cells can confirm its role in 5-FU sensitivity.
Point Mutation
Introducing specific point mutations into the UMPS gene via CRISPR base editing or homology-directed repair allows researchers to dissect the catalytic mechanism and identify residues critical for OPRT activity. Such models can also mimic naturally occurring mutations in orotic aciduria.
Knock-in
Knock-in of fluorescent tags (e.g., GFP) or epitope tags at the endogenous UMPS locus enables real-time visualization and purification of OPRT for interaction studies. This approach preserves native regulation and expression levels.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression of UMPS can create cell lines with elevated OPRT activity. These models are valuable for studying the effects of OPRT overexpression on cancer cell proliferation, drug response, and prognosis.
How EDITGENE Supports orotate phosphoribosyltransferase activity Research
Researchers studying orotate phosphoribosyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in pyrimidine metabolism, cancer progression, or drug resistance. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models, enabling functional validation and mechanistic studies.
Contact EDITGENE today to design your custom CRISPR model for orotate phosphoribosyltransferase activity research.
Frequently Asked Questions About orotate phosphoribosyltransferase activity
What is orotate phosphoribosyltransferase activity?
It is the enzymatic activity (GO:0004588) that catalyzes the conversion of orotate to orotidine 5'-monophosphate (OMP) using PRPP, a key step in pyrimidine biosynthesis.
What genes are involved in orotate phosphoribosyltransferase activity?
The primary gene is UMPS in humans, which encodes a bifunctional enzyme with OPRT and OMPDC activities. In other organisms, genes like pyrE and PYR5,6 are involved.
How is OPRT activity measured?
It can be measured using a fluorometric assay that detects orotic acid, or spectrophotometric assays monitoring OMP formation.
What diseases are associated with OPRT activity?
Altered OPRT activity is linked to renal cell carcinoma, bladder carcinoma, gastric cancer resistance to 5-FU, and malignant pleural mesothelioma.
Is OPRT a good cancer biomarker?
Yes, studies show that OPRT activity correlates with prognosis in renal and bladder cancers, and its expression predicts response to therapy in mesothelioma.
Can CRISPR be used to study OPRT?
Absolutely. CRISPR knockout, knock-in, and point mutation models allow precise dissection of OPRT function in cells and its role in disease.
What is the reaction catalyzed by OPRT?
OPRT catalyzes: orotidine 5'-phosphate + diphosphate = orotate + 5-phospho-alpha-D-ribose 1-diphosphate.
Why is OPRT important for chemotherapy?
OPRT activates 5-fluorouracil, and decreased activity leads to drug resistance in gastric cancer.
Are there bifunctional OPRT enzymes?
Yes, in Plasmodium falciparum, OPRT is fused with OMPDC to form a bifunctional enzyme.
How does OPRT relate to pyrimidine biosynthesis?
OPRT catalyzes the fifth step in de novo pyrimidine biosynthesis, producing OMP, which is then decarboxylated to UMP.
Conclusion
Orotate phosphoribosyltransferase activity (GO:0004588) is a fundamental enzymatic function in pyrimidine biosynthesis with critical roles in cancer biology, drug resistance, and pathogen metabolism. Its dysregulation has been linked to prognosis in multiple cancers and resistance to 5-fluorouracil. Understanding OPRT at the molecular level offers opportunities for biomarker development and targeted therapies. EDITGENE's CRISPR services empower researchers to create precise cell models for studying OPRT and its related pathways.
References
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- 2. Paojinda P et al.. 2018. Bifunctional activity of fused Plasmodium falciparum orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase.. Parasitol Int 67(1):79-84 PMID: 28389349
- 3. Mizutani Y et al.. 2004. Significance of orotate phosphoribosyltransferase activity in renal cell carcinoma.. J Urol 171(2 Pt 1):605-10 PMID: 14713770
- 4. Mizutani Y et al.. 2004. Prognostic significance of orotate phosphoribosyltransferase activity in bladder carcinoma.. Cancer 100(4):723-31 PMID: 14770427
- 5. Hamana H et al.. 1999. Effects of C-terminal deletion on the activity and thermostability of orotate phosphoribosyltransferase from Thermus thermophilus.. J Biochem 125(1):109-14 PMID: 9880805
- 6. Yoshimoto A et al.. 1978. Orotate phosphoribosyltransferase (yeast).. Methods Enzymol 51:69-74 PMID: 357907
- 7. Tsutani Y et al.. 2008. Decreased orotate phosphoribosyltransferase activity produces 5-fluorouracil resistance in a human gastric cancer cell line.. Oncol Rep 20(6):1545-51 PMID: 19020740
- 8. Hamamoto Y et al.. 2016. Orotate phosphoribosyltransferase is overexpressed in malignant pleural mesothelioma: Dramatically responds one case in high OPRT expression.. Rare Dis 4(1):e1165909 PMID: 27274438
