GO:0030412 formimidoyltetrahydrofolate cyclodeaminase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0030412 describes the enzymatic activity that converts 5-formimidoyltetrahydrofolate to 5,10-methenyltetrahydrofolate and ammonium, a key step in one-carbon metabolism.
• In mammals, this activity is carried by the bifunctional enzyme formimidoyltransferase cyclodeaminase (FTCD), which also transfers formimino groups from formiminoglutamate to tetrahydrofolate.
• The deaminase activity of FTCD requires a reduced sulfhydryl group, and its loss impairs folate-dependent one-carbon flux.
• FTCD loss in liver promotes lipid accumulation and hepatocarcinogenesis through upregulation of PPARγ and SREBP2.
• FTCD is a potential therapeutic target and delivery of FTCD plasmids has been explored for MRI-guided tetrahydrofolate metabolism modulation in hepatocellular carcinoma.
• Cyclodeaminase-type enzymes are structurally and mechanistically diverse, with homologs in bacteria, fungi, and mammals that catalyze related imine reduction or ammonia elimination reactions.
Description
Formimidoyltetrahydrofolate cyclodeaminase activity (GO:0030412) is a molecular function that catalyzes the cyclization and deamination of 5-formimidoyltetrahydrofolate to produce 5,10-methenyltetrahydrofolate and ammonium. This reaction is a critical node in folate-mediated one-carbon metabolism, linking histidine catabolism to the generation of one-carbon units used in nucleotide biosynthesis and methylation reactions. In mammals, the activity resides in the bifunctional enzyme formimidoyltransferase cyclodeaminase (FTCD), which couples the transfer of a formimino group from formiminoglutamate to tetrahydrofolate with the subsequent cyclodeamination of the intermediate. Researchers study this activity to understand how one-carbon flux is regulated and how its disruption contributes to metabolic disease and cancer. The enzyme has been purified and characterized from porcine and other sources, revealing essential cysteine residues and kinetic properties that define its catalytic mechanism. Beyond mammals, cyclodeaminase homologs from bacteria and fungi have provided structural and mechanistic insights into imine reduction and ammonia elimination reactions. Because FTCD sits at the intersection of amino acid catabolism and folate metabolism, its dysfunction has been linked to altered lipid homeostasis and hepatocellular carcinoma.
formimidoyltetrahydrofolate cyclodeaminase activity At A Glance
| GO ID | GO:0030412 |
|---|---|
| GO term | formimidoyltetrahydrofolate cyclodeaminase activity |
| Ontology | molecular_function |
| Synonym | 5-formimidoyltetrahydrofolate ammonia-lyase (cyclizing) |
| Synonym | formiminotetrahydrofolate cyclodeaminase activity |
| Definition | Catalysis of the reaction: 5-formimidoyltetrahydrofolate + 2 H+ = 5,10-methenyltetrahydrofolate + NH4. |
| Major function | Converts 5-formimidoyltetrahydrofolate to 5,10-methenyltetrahydrofolate, releasing ammonium; key step in one-carbon metabolism. |
| Cofactor | Requires a reduced sulfhydryl group for deaminase activity. |
| Associated enzyme | Formimidoyltransferase cyclodeaminase (FTCD) in mammals. |
What Is GO:0030412?
GO:0030412 formimidoyltetrahydrofolate cyclodeaminase activity is defined as the catalysis of the reaction: 5-formimidoyltetrahydrofolate + 2 H+ = 5,10-methenyltetrahydrofolate + NH4. In other words, it is the enzyme activity that removes ammonia from 5-formimidoyltetrahydrofolate and cyclizes the molecule to form 5,10-methenyltetrahydrofolate, a central one-carbon donor in folate metabolism.
Why Is formimidoyltetrahydrofolate cyclodeaminase activity Important in Cell Biology?
Formimidoyltetrahydrofolate cyclodeaminase activity is important because it directly supplies 5,10-methenyltetrahydrofolate, a central one-carbon donor for thymidylate and purine synthesis, and it links histidine catabolism to folate pools. Dysregulation of this activity alters one-carbon flux, which can affect lipid metabolism and promote hepatocarcinogenesis. The enzyme FTCD has also been investigated as a therapeutic target and imaging agent in hepatocellular carcinoma, underscoring its clinical relevance.
• Provides 5,10-methenyltetrahydrofolate for nucleotide biosynthesis and methylation reactions.
• Connects histidine catabolism to folate-mediated one-carbon metabolism.
• Loss of FTCD promotes lipid accumulation and hepatocarcinogenesis via PPARγ and SREBP2 upregulation.
• FTCD plasmid delivery has been explored for MRI-guided tetrahydrofolate metabolism modulation in hepatocellular carcinoma.
• The deaminase activity depends on a reduced sulfhydryl group, making it sensitive to oxidative regulation.
• Cyclodeaminase homologs in bacteria and fungi inform general mechanisms of imine reduction and ammonia elimination.
• FTCD is a bifunctional enzyme, so mutations can selectively affect transferase or deaminase activity.
• Altered one-carbon metabolism is a metabolic vulnerability in several cancers, making this activity a potential target.
Molecular Mechanism of formimidoyltetrahydrofolate cyclodeaminase activity
Substrate binding and formimino group transfer
In simple terms: The enzyme first picks up a formimino group from a donor molecule and attaches it to tetrahydrofolate.
In the bifunctional FTCD enzyme, the transferase domain catalyzes the transfer of a formimino group from formiminoglutamate to tetrahydrofolate, generating 5-formimidoyltetrahydrofolate. This step is part of histidine catabolism and prepares the substrate for the subsequent cyclodeaminase reaction.
Cyclization and ammonia release
In simple terms: The enzyme then removes ammonia from the intermediate and closes a ring to form a new folate derivative.
The cyclodeaminase domain catalyzes the removal of ammonia from 5-formimidoyltetrahydrofolate, accompanied by cyclization to form 5,10-methenyltetrahydrofolate. This reaction releases ammonium and generates a one-carbon unit at the methenyl level, which can be further reduced for biosynthetic reactions.
Role of essential sulfhydryl groups
In simple terms: A reactive sulfur group in the enzyme must be in its reduced form for the deaminase step to work.
Studies on formiminotransferase-cyclodeaminase from porcine liver have shown that a sulfhydryl group is essential for the deaminase activity of the bifunctional enzyme. Chemical modification or oxidation of this cysteine residue impairs the cyclodeaminase reaction, indicating a key catalytic or structural role.
Kinetic properties and substrate specificity
In simple terms: The enzyme works faster or slower depending on the type of folate substrate and its polyglutamate tail.
Kinetic analyses of purified pig liver formiminotransferase-cyclodeaminase with tetrahydropteroylpolyglutamates have revealed differences in transferase activity depending on the polyglutamate chain length. These studies provide a framework for understanding how folate substrate forms influence the overall bifunctional reaction.
Structural and mechanistic insights from homologs
In simple terms: Similar enzymes in bacteria and fungi help scientists understand how this type of reaction works.
Cyclodeaminase homologs such as lysine cyclodeaminase from Streptomyces pristinaespiralis and an ornithine cyclodeaminase/μ-crystallin homolog from Candida parapsilosis have been biochemically and structurally characterized. These studies reveal diverse mechanisms for imine reduction and ammonia elimination, providing comparative insights into the formimidoyltetrahydrofolate cyclodeaminase reaction.
Key Genes Involved in GO:0030412 formimidoyltetrahydrofolate cyclodeaminase activity
The following genes and proteins are directly or functionally associated with formimidoyltetrahydrofolate cyclodeaminase activity and related one-carbon metabolism.
| Gene | Major Role | Research Relevance |
|---|---|---|
| FTCD | Bifunctional enzyme with formiminotransferase and cyclodeaminase activities; carries GO:0030412 in mammals | Central to one-carbon metabolism; loss promotes hepatocarcinogenesis |
| MTHFR | Reduces 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate | Regulates folate cycle flux downstream of methenyl-THF |
| MTHFD1 | Interconverts tetrahydrofolate derivatives including 5,10-methenyl-THF | Maintains one-carbon pools linked to cyclodeaminase product |
| MTHFD2 | Mitochondrial one-carbon enzyme producing 5,10-methenyl-THF | Supports mitochondrial one-carbon flux |
| SHMT1 | Serine hydroxymethyltransferase, generates 5,10-methylene-THF | Connects serine metabolism to folate cycle |
| SHMT2 | Mitochondrial serine hydroxymethyltransferase | Provides one-carbon units in mitochondria |
| GART | Phosphoribosylglycinamide formyltransferase, uses 10-formyl-THF | Purine biosynthesis downstream of methenyl-THF |
| ATIC | Bifunctional purine biosynthesis enzyme using 10-formyl-THF | Links folate cycle to purine synthesis |
| TYMS | Thymidylate synthase, uses 5,10-methylene-THF | Nucleotide biosynthesis connected to folate pools |
| DHFR | Dihydrofolate reductase, regenerates tetrahydrofolate | Maintains folate cycle |
| MTR | Methionine synthase, uses 5-methyl-THF | Connects folate cycle to methylation |
| PPARG | Nuclear receptor upregulated upon FTCD loss | Mediates lipid accumulation in FTCD-deficient liver |
| SREBP2 | Sterol regulatory element-binding protein 2, upregulated with FTCD loss | Drives lipogenesis and hepatocarcinogenesis |
| HIST1H1C | Histidine catabolism-related enzyme (formiminotransferase cyclodeaminase superfamily member) | Histidine degradation feeds formimino groups into folate cycle |
| GLUD1 | Glutamate dehydrogenase, releases ammonia in amino acid catabolism | Ammonia handling related to cyclodeaminase reaction |
| ASL | Argininosuccinate lyase, ammonia-releasing enzyme | Nitrogen mobilization context |
| OTC | Ornithine transcarbamylase, urea cycle enzyme | Ammonia detoxification linked to nitrogen metabolism |
| ARG1 | Arginase 1, urea cycle enzyme | Nitrogen mobilization and ammonia production |
How Is formimidoyltetrahydrofolate cyclodeaminase activity Regulated?
The activity of formimidoyltetrahydrofolate cyclodeaminase is regulated at multiple levels. The bifunctional FTCD enzyme requires a reduced sulfhydryl group for deaminase activity, so oxidative modification of critical cysteine residues can inhibit the reaction. Substrate availability, particularly the polyglutamylation state of tetrahydrofolate, influences the kinetics of the transferase and deaminase reactions. In liver, loss of FTCD leads to compensatory upregulation of PPARγ and SREBP2, indicating that the pathway is connected to transcriptional programs controlling lipid metabolism. Additionally, nitrogen mobilization pathways involving arginine and ornithine metabolism can influence ammonia levels that may affect the reaction environment.
formimidoyltetrahydrofolate cyclodeaminase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| FTCD | Hepatocellular carcinoma, lipid accumulation | FTCD knockout hepatocytes and mouse liver models |
| FTCD | Tetrahydrofolate metabolism modulation in liver cancer | FTCD plasmid delivery with MRI nanotheranostics |
| PPARG | Lipid accumulation downstream of FTCD loss | PPARγ overexpression or knockout in liver cells |
| SREBP2 | Lipogenesis and hepatocarcinogenesis | SREBP2 knockdown or overexpression in FTCD-deficient cells |
| MTHFD1 | One-carbon metabolism imbalance | MTHFD1 knockout cell lines |
Hepatocellular carcinoma and lipid accumulation
Loss of hepatic FTCD promotes lipid accumulation and hepatocarcinogenesis by upregulating PPARγ and SREBP2. This links formimidoyltetrahydrofolate cyclodeaminase activity directly to liver cancer development and metabolic reprogramming. FTCD plasmid delivery has been explored as a strategy to modulate tetrahydrofolate metabolism in hepatocellular carcinoma, with potential for MRI-guided nanotheranostics.
One-carbon metabolism disorders
Because the cyclodeaminase reaction supplies 5,10-methenyltetrahydrofolate, impaired activity can disrupt nucleotide biosynthesis and methylation reactions. Such disruptions may contribute to metabolic imbalances, although specific inherited disorders of FTCD are not well characterized in the cited literature.
Nitrogen metabolism and ammonia handling
The reaction releases ammonium, connecting it to nitrogen mobilization pathways. In organisms ranging from cyanobacteria to mammals, arginine and ornithine catabolism intersect with ammonia production and detoxification. Cyclodeaminase homologs in bacteria and fungi further highlight the evolutionary importance of ammonia-releasing reactions.
From formimidoyltetrahydrofolate cyclodeaminase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of FTCD cyclodeaminase activity alter one-carbon flux? | FTCD knockout cell lines (e.g., HepG2, primary hepatocytes) |
| Which cysteine residue is essential for deaminase activity? | Point-mutation knock-in of cysteine-to-serine in FTCD |
| Can restored FTCD activity reverse lipid accumulation? | Knock-in or overexpression of wild-type FTCD in FTCD-null cells |
| How does FTCD loss affect PPARγ and SREBP2 transcription? | FTCD knockout with RNA-seq and ChIP-seq |
| Can FTCD be targeted for imaging in liver cancer? | FTCD plasmid-loaded nanotheranostics in xenograft models |
| What is the role of FTCD in histidine catabolism? | Metabolic tracing with 13C-histidine in FTCD knockout cells |
How to Study the formimidoyltetrahydrofolate cyclodeaminase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Spectrophotometric enzyme assay | Formation of 5,10-methenyltetrahydrofolate | Purified FTCD activity and inhibitor testing |
| Stable isotope tracing | Flux through one-carbon metabolism | Histidine/serine tracing in cells |
| RNA-seq | Transcriptional changes after FTCD loss | Identifying PPARγ/SREBP2 upregulation |
| Proteomics | Protein expression and modification | Assessing FTCD and pathway proteins |
| MRI nanotheranostics | Tumor imaging and drug delivery | FTCD plasmid delivery in HCC models |
| Site-directed mutagenesis | Role of specific residues | Cysteine-to-serine FTCD mutants |
| Kinetic analysis | Substrate affinity and turnover | Polyglutamate substrate specificity |
| Homolog biochemistry | Mechanistic comparisons | Bacterial/fungal cyclodeaminases |
Enzymatic assays for cyclodeaminase activity
Direct measurement of formimidoyltetrahydrofolate cyclodeaminase activity can be performed using purified enzyme and spectrophotometric monitoring of 5,10-methenyltetrahydrofolate formation. Such assays have been used to characterize the bifunctional FTCD enzyme and to test the role of essential sulfhydryl groups.
Metabolic tracing and one-carbon flux analysis
Stable isotope tracing with labeled histidine or serine can quantify flux through the folate cycle and assess how loss of FTCD affects one-carbon distribution. These methods are useful for linking cyclodeaminase activity to nucleotide synthesis and methylation.
Transcriptomic and proteomic profiling
RNA-seq and proteomics can identify transcriptional and post-translational changes following FTCD loss, such as upregulation of PPARγ and SREBP2. Such profiling helps define the downstream consequences of altered cyclodeaminase activity.
Imaging and nanotheranostics
FTCD plasmid incorporation into hollow mesoporous organosilica nanotheranostics has been used for magnetic resonance imaging and tetrahydrofolate metabolism modulation in hepatocellular carcinoma models. This approach combines therapeutic delivery with imaging readouts.
How CRISPR Can Be Used to Study GO:0030412 formimidoyltetrahydrofolate cyclodeaminase activity
Knockout
CRISPR knockout of FTCD can eliminate formimidoyltetrahydrofolate cyclodeaminase activity, enabling studies of one-carbon flux, lipid accumulation, and hepatocarcinogenesis. FTCD knockout cell lines are valuable for testing whether restored activity reverses metabolic phenotypes.
Point Mutation
Point mutations in FTCD, such as cysteine-to-serine substitutions, can be introduced to test the role of essential sulfhydryl groups in deaminase activity. Such models help dissect catalytic residues from structural ones.
Knock-in
Knock-in of tagged or wild-type FTCD allows controlled expression and localization studies in cells lacking endogenous activity. This approach can also be used to restore cyclodeaminase function in disease models.
Overexpression
Overexpression of FTCD or its domains can amplify cyclodeaminase activity, facilitating biochemical purification and kinetic studies. It also enables testing of downstream effects on PPARγ and SREBP2.
How EDITGENE Supports formimidoyltetrahydrofolate cyclodeaminase activity Research
Researchers studying formimidoyltetrahydrofolate cyclodeaminase activity-related genes often need to determine whether a candidate gene is causally involved in one-carbon metabolism, lipid homeostasis, or cancer phenotypes. EDITGENE provides CRISPR-based cell model services to support such investigations with reproducible and publication-ready reagents.
Contact EDITGENE today to design your custom CRISPR model for formimidoyltetrahydrofolate cyclodeaminase activity research.
Frequently Asked Questions About formimidoyltetrahydrofolate cyclodeaminase activity
What is formimidoyltetrahydrofolate cyclodeaminase activity?
It is the enzyme activity defined by GO:0030412 that converts 5-formimidoyltetrahydrofolate to 5,10-methenyltetrahydrofolate and ammonium.
What is the GO ID for formimidoyltetrahydrofolate cyclodeaminase activity?
The GO ID is GO:0030412.
Which gene encodes formimidoyltetrahydrofolate cyclodeaminase activity in humans?
In mammals, the bifunctional enzyme FTCD carries this activity.
What reaction does GO:0030412 catalyze?
It catalyzes 5-formimidoyltetrahydrofolate + 2 H+ = 5,10-methenyltetrahydrofolate + NH4.
Why is formimidoyltetrahydrofolate cyclodeaminase activity important in cancer?
Loss of FTCD promotes lipid accumulation and hepatocarcinogenesis via PPARγ and SREBP2 upregulation.
What diseases are linked to FTCD dysfunction?
FTCD loss has been linked to hepatocellular carcinoma and altered tetrahydrofolate metabolism.
How is formimidoyltetrahydrofolate cyclodeaminase activity measured?
It can be measured by spectrophotometric assays monitoring 5,10-methenyltetrahydrofolate formation.
Does the enzyme require any cofactors?
The deaminase activity requires a reduced sulfhydryl group for catalysis.
What are homologs of formimidoyltetrahydrofolate cyclodeaminase?
Homologs include lysine cyclodeaminase from Streptomyces and ornithine cyclodeaminase/μ-crystallin from Candida.
How can CRISPR help study GO:0030412?
CRISPR knockout, point mutation, knock-in, and overexpression models allow functional dissection of FTCD and related genes.
Conclusion
Formimidoyltetrahydrofolate cyclodeaminase activity (GO:0030412) is a central enzymatic step in one-carbon metabolism, converting 5-formimidoyltetrahydrofolate to 5,10-methenyltetrahydrofolate and ammonium. In mammals, this activity is carried by the bifunctional FTCD enzyme, whose loss promotes lipid accumulation and hepatocarcinogenesis through PPARγ and SREBP2. The reaction depends on a reduced sulfhydryl group and is influenced by folate substrate polyglutamylation. Beyond mammals, cyclodeaminase homologs provide mechanistic insights into imine reduction and ammonia elimination. Targeting this activity with CRISPR-based models offers a promising approach to dissect its roles in cancer and metabolic disease.
References
- 1. Wang S et al.. 2023. Loss of hepatic FTCD promotes lipid accumulation and hepatocarcinogenesis by upregulating PPARγ and SREBP2.. JHEP Rep 5(10):100843 PMID: 37675273
- 2. Zhang H et al.. 2019. Arginine and nitrogen mobilization in cyanobacteria.. Mol Microbiol 111(4):863-867 PMID: 30656751
- 3. Uma Mahesh VNM et al.. 2021. Imine reduction by an Ornithine cyclodeaminase/μ-crystallin homolog purified from Candida parapsilosis ATCC 7330.. Biotechnol Rep (Amst) 31:e00664 PMID: 34557391
- 4. Ying H et al.. 2018. Studies of lysine cyclodeaminase from Streptomyces pristinaespiralis: Insights into the complex transition NAD(+) state.. Biochem Biophys Res Commun 495(1):306-311 PMID: 29122596
- 5. Findlay WA et al.. 1989. An improved procedure for the purification of formiminotransferase-cyclodeaminase from pig liver. Kinetics of the transferase activity with tetrahydropteroylpolyglutamates.. Biochim Biophys Acta 999(1):52-7 PMID: 2572277
- 6. Tsotsou GE et al.. 2007. Biochemical characterisation of recombinant Streptomyces pristinaespiralis L-lysine cyclodeaminase.. Biochimie 89(5):591-604 PMID: 17291665
- 7. Chen J et al.. 2022. Hollow mesoporous organosilica nanotheranostics incorporating formimidoyltransferase cyclodeaminase (FTCD) plasmids for magnetic resonance imaging and tetrahydrofolate metabolism fission on hepatocellular carcinoma.. Int J Pharm 612:121281 PMID: 34774692
- 8. Drury EJ et al.. 1977. Formiminotransferase-cyclodeaminase from porcine liver. A sulfhydryl essential for the deaminase activity of the bifunctional enzyme.. Can J Biochem 55(9):919-23 PMID: 561642
