GO:0019346 transsulfuration: Cysteine Homeostasis, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0019346 transsulfuration is the interconversion of homocysteine and cysteine via cystathionine, a central hub linking methionine metabolism to antioxidant defense.
• The pathway is catalyzed by cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CTH), with alternative routes in yeast and bacteria.
• Transsulfuration supports cysteine homeostasis, glutathione synthesis, and hydrogen sulfide production, influencing redox balance and cell survival.
• Dysregulation of transsulfuration is implicated in Parkinson's disease, schizophrenia, rheumatoid arthritis, COPD, and cancer.
• In cancer, transsulfuration can be a minor player or crucial for cysteine homeostasis depending on tumor context.
• CRISPR knockout, point mutation, knock-in, and overexpression models enable causal dissection of transsulfuration genes in disease and metabolism.
Description
Transsulfuration (GO:0019346) is the biological process that interconverts homocysteine and cysteine via the intermediate cystathionine. This pathway is essential for maintaining cysteine levels when dietary methionine is limited, and it provides the sulfur needed for glutathione and hydrogen sulfide production. In mammals, transsulfuration is irreversible and occurs mainly in the liver, kidney, and pancreas, while in Saccharomyces cerevisiae two separate transsulfuration pathways exist. Researchers study transsulfuration because it connects one-carbon metabolism, redox homeostasis, and neuromodulation, and its dysfunction is linked to neurodegeneration, psychiatric disorders, inflammatory diseases, and cancer. Understanding the genes and regulatory mechanisms of transsulfuration is therefore critical for developing targeted therapies and biomarkers.
transsulfuration At A Glance
| GO ID | GO:0019346 |
|---|---|
| GO term | transsulfuration |
| Ontology | biological_process |
| Synonym | homocysteine-cysteine interconversion; transsulphuration |
| Major function | Interconversion of homocysteine and cysteine via cystathionine |
| Key enzymes | CBS, CTH, and in yeast STR2/STR3 |
| Pathway context | Methionine metabolism, cysteine biosynthesis, glutathione production |
| Disease relevance | Parkinson's disease, schizophrenia, rheumatoid arthritis, COPD, cancer |
What Is GO:0019346?
According to the Gene Ontology, GO:0019346 transsulfuration is defined as the interconversion of homocysteine and cysteine via cystathionine. In contrast with enteric bacteria and mammals, Saccharomyces cerevisiae has two transsulfuration pathways employing two separate sets of enzymes. The term is synonymous with homocysteine-cysteine interconversion and transsulphuration.
Why Is transsulfuration Important in Cell Biology?
Transsulfuration is a metabolic crossroads that determines cysteine availability for protein synthesis, glutathione, and hydrogen sulfide, thereby influencing cellular redox state and signaling. Its dysregulation has been associated with a wide range of human diseases, including neurodegenerative and psychiatric disorders, autoimmune conditions, and cancer, making it a target for biomarker and therapeutic research.
• Maintains cysteine homeostasis when methionine is limiting.
• Supplies cysteine for glutathione synthesis, a major cellular antioxidant.
• Produces hydrogen sulfide, a gasotransmitter with neuromodulatory and cytoprotective roles.
• Linked to Parkinson's disease through neuromodulation and oxidative stress.
• Implicated in treatment-resistant schizophrenia via redox and methylation imbalances.
• Associated with rheumatoid arthritis in systematic reviews and meta-analyses.
• Shows altered metabolomics in chronic obstructive pulmonary disease.
• Essential for ferroptosis resistance in quiescent endothelial cells.
• Provides a metabolic vulnerability in certain cancers.
• Offers targets for CRISPR-based functional studies and drug discovery.
What Happens During transsulfuration?
Condensation of homocysteine and serine to cystathionine
In simple terms: The first step attaches homocysteine to serine to form cystathionine.
Cystathionine beta-synthase (CBS) catalyzes the condensation of homocysteine with serine to form cystathionine, a reaction that requires pyridoxal 5'-phosphate (PLP) as a cofactor. This step commits homocysteine to the transsulfuration pathway and is regulated by S-adenosylmethionine (SAM) in mammals.
Cleavage of cystathionine to cysteine and alpha-ketobutyrate
In simple terms: The second step breaks cystathionine to release cysteine.
Cystathionine gamma-lyase (CTH) cleaves cystathionine into cysteine, alpha-ketobutyrate, and ammonia. This reaction is also PLP-dependent and completes the net conversion of homocysteine to cysteine.
Alternative transsulfuration routes in yeast
In simple terms: Yeast use two different enzyme sets to do the same interconversion.
In Saccharomyces cerevisiae, two separate transsulfuration pathways exist: one using cystathionine beta-synthase and cystathionine gamma-lyase, and another using cystathionine gamma-synthase and cystathionine beta-lyase. This contrasts with enteric bacteria and mammals, which typically employ a single pathway.
Coupling to methionine cycle and one-carbon metabolism
In simple terms: Transsulfuration is tied to the methionine cycle, so changes in one affect the other.
Transsulfuration is irreversible in mammals and drains homocysteine from the methionine cycle, linking it to folate and one-carbon metabolism. This connection is relevant in diseases where folate status and homocysteine levels are altered, such as rheumatoid arthritis and COPD.
Production of hydrogen sulfide and glutathione precursors
In simple terms: The pathway also makes signaling molecules and antioxidant building blocks.
CBS and CTH can produce hydrogen sulfide (H2S) from homocysteine or cysteine, and the cysteine generated feeds glutathione synthesis. These products contribute to redox balance, neuromodulation, and ferroptosis resistance.
Key Genes Involved in GO:0019346 transsulfuration
The following genes and proteins are central to transsulfuration, as supported by published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CBS | Condenses homocysteine and serine to cystathionine | Mutations cause homocystinuria; target in neurodegeneration and cancer |
| CTH | Cleaves cystathionine to cysteine and alpha-ketobutyrate | Regulates cysteine and H2S; implicated in cancer and endothelial ferroptosis |
| MTR | Methionine synthase, regenerates methionine from homocysteine | Links folate cycle to transsulfuration |
| MTHFR | Reduces 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate | Affects homocysteine remethylation and transsulfuration flux |
| MAT1A | Synthesizes SAM, activator of CBS | Regulates transsulfuration via SAM |
| GCLC | Glutamate-cysteine ligase catalytic subunit | Uses cysteine for glutathione synthesis |
| GCLM | Glutamate-cysteine ligase modifier subunit | Regulates glutathione synthesis |
| SLC7A11 | Cystine/glutamate antiporter | Influences cysteine availability and ferroptosis |
| GPX4 | Glutathione peroxidase 4 | Protects against lipid peroxidation; linked to transsulfuration products |
| STR2 | Yeast cystathionine gamma-synthase | Alternative transsulfuration in S. cerevisiae |
| STR3 | Yeast cystathionine beta-lyase | Alternative transsulfuration in S. cerevisiae |
| CYS4 | Yeast cystathionine beta-synthase | Transsulfuration in S. cerevisiae |
| CYS3 | Yeast cystathionine gamma-lyase | Transsulfuration in S. cerevisiae |
| NFE2L2 | Transcription factor regulating antioxidant genes | May influence transsulfuration gene expression |
| ATF4 | Integrated stress response transcription factor | Regulates amino acid metabolism including transsulfuration |
| XBP1 | Unfolded protein response transcription factor | Linked to transsulfuration regulation |
How Is transsulfuration Regulated?
Transsulfuration is regulated at multiple levels. In mammals, CBS is activated by S-adenosylmethionine (SAM) and inhibited by oxidative stress, while CTH expression is influenced by the integrated stress response (ISR) and transcription factors such as ATF4 and NFE2L2. The pathway is also subject to feedback regulation by cysteine and glutathione levels, and it cross-talks with the methionine cycle and folate metabolism. In cancer, oncogenic signaling can reprogram transsulfuration to support antioxidant defense and proliferation. In endothelial cells, transsulfuration metabolism is essential for ferroptosis resistance, highlighting context-dependent regulation.
transsulfuration and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CBS | Parkinson's disease, homocystinuria | Knockout or point-mutation in neuronal cell lines |
| CTH | Cancer, ferroptosis resistance | Knockout in cancer or endothelial cells |
| MTHFR | Rheumatoid arthritis, COPD | Overexpression or point mutation in immune cells |
| SLC7A11 | Ferroptosis, cancer | Knockout or overexpression in cancer cells |
| GPX4 | Ferroptosis | Knockout or point mutation in endothelial cells |
Transsulfuration in Parkinson's disease
Transsulfuration pathway metabolites, including homocysteine and cysteine, have been proposed as neuromodulators in Parkinson's disease, where oxidative stress and mitochondrial dysfunction are central. Alterations in CBS and CTH activity may affect H2S production and redox balance, contributing to neurodegeneration.
Transsulfuration in schizophrenia
Treatment-resistant schizophrenia has been associated with abnormalities in the transsulfuration pathway, potentially linking redox dysregulation and methylation imbalances to symptom severity. Studies suggest that targeting this pathway could offer novel therapeutic strategies.
Transsulfuration in rheumatoid arthritis and COPD
Systematic reviews and meta-analyses have shown that transsulfuration and folate pathway metabolites are altered in rheumatoid arthritis, and metabolomic changes in arginine, transsulfuration, and folic acid pathways are observed in chronic obstructive pulmonary disease. These findings suggest shared metabolic dysregulation in inflammatory and oxidative stress-related conditions.
Transsulfuration in cancer and ferroptosis
In cancer, transsulfuration can be a minor player or crucial for cysteine homeostasis depending on the tumor microenvironment and genetic background. Additionally, transsulfuration metabolism is essential for ferroptosis resistance in quiescent endothelial cells, linking cysteine availability to lipid peroxidation and cell death.
From transsulfuration-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does CBS loss alter cysteine homeostasis? | CBS knockout cell line |
| Does a CBS point mutation affect H2S production? | CBS point-mutation knock-in |
| Does CTH overexpression protect against ferroptosis? | CTH overexpression cell model |
| Does tagging CTH affect its localization? | Tagged knock-in of CTH |
| Does SLC7A11 knockout sensitize to ferroptosis? | SLC7A11 knockout cell line |
| Does MTHFR polymorphism affect transsulfuration flux? | MTHFR point-mutation knock-in |
How to Study the transsulfuration Process
| Method | What It Measures | Typical Application |
|---|---|---|
| LC-MS metabolomics | Levels of homocysteine, cystathionine, cysteine, glutathione | Quantify pathway activity in cells or tissues |
| Stable isotope tracing | Flux through transsulfuration | Determine metabolic rewiring in cancer |
| RNA-seq | mRNA expression of CBS, CTH, etc. | Identify regulatory changes in disease models |
| Western blot | Protein levels and modifications | Validate expression and signaling |
| H2S detection assay | Hydrogen sulfide production | Assess CBS/CTH activity |
| Glutathione assay | Reduced/oxidized glutathione ratio | Measure redox balance |
| CRISPR knockout screen | Gene essentiality and pathway dependencies | Discover modulators of transsulfuration |
| Bioinformatics meta-analysis | Pathway enrichment and biomarker signatures | Integrate public omics data |
Metabolomics and flux analysis
Mass spectrometry-based metabolomics can quantify homocysteine, cystathionine, cysteine, and glutathione to assess transsulfuration activity. Stable isotope tracing can measure flux through the pathway.
Gene expression and proteomics
RNA-seq and proteomics can measure expression of CBS, CTH, and related genes under different conditions, revealing regulatory mechanisms. Western blotting can confirm protein levels and post-translational modifications.
Functional assays for H2S and redox
Hydrogen sulfide production can be measured using colorimetric or fluorescent probes, and glutathione levels can be assayed to assess redox status. Ferroptosis sensitivity can be tested with lipid peroxidation markers.
CRISPR screening and bioinformatics
Genome-wide CRISPR knockout screens can identify genes that modulate transsulfuration and related metabolic vulnerabilities. Bioinformatics analysis of public datasets can reveal pathway dysregulation in disease.
How CRISPR Can Be Used to Study GO:0019346 transsulfuration
Knockout
CRISPR knockout of CBS or CTH can abolish transsulfuration, leading to cysteine auxotrophy and altered redox status, which is useful for studying pathway dependencies in cancer and neurodegeneration.
Point Mutation
Introducing disease-associated point mutations in CBS or CTH via CRISPR can model enzyme deficiencies and assess their impact on homocysteine and H2S levels.
Knock-in
Tagged knock-in of CBS or CTH with fluorescent or affinity tags enables real-time localization and interaction studies in live cells.
Overexpression
Overexpression of CTH or CBS can enhance H2S production and protect against oxidative stress or ferroptosis, providing gain-of-function models for therapeutic exploration.
How EDITGENE Supports transsulfuration Research
Researchers studying transsulfuration-related genes often need to determine whether a candidate gene is causally involved in cysteine homeostasis, redox regulation, or disease phenotypes. EDITGENE provides comprehensive CRISPR services to enable such functional studies with high precision and reproducibility.
Contact EDITGENE today to design your custom CRISPR model for transsulfuration research.
Frequently Asked Questions About transsulfuration
What is transsulfuration?
Transsulfuration is the interconversion of homocysteine and cysteine via cystathionine, a key metabolic pathway for cysteine homeostasis.
What genes are involved in transsulfuration?
Key genes include CBS, CTH, and in yeast STR2, STR3, CYS3, and CYS4.
What is the GO ID for transsulfuration?
The Gene Ontology ID for transsulfuration is GO:0019346.
How is transsulfuration regulated?
It is regulated by SAM, oxidative stress, the integrated stress response, and transcription factors such as ATF4 and NFE2L2.
What diseases are linked to transsulfuration?
It is linked to Parkinson's disease, schizophrenia, rheumatoid arthritis, COPD, and cancer.
What is the role of CBS in transsulfuration?
CBS catalyzes the condensation of homocysteine and serine to form cystathionine.
What is the role of CTH in transsulfuration?
CTH cleaves cystathionine to cysteine and alpha-ketobutyrate.
How can I study transsulfuration with CRISPR?
CRISPR knockout, point mutation, knock-in, and overexpression models can be used to dissect gene function in this pathway.
Is transsulfuration important in cancer?
Yes, it can be crucial for cysteine homeostasis and antioxidant defense in certain cancers.
What is the connection between transsulfuration and ferroptosis?
Transsulfuration supports glutathione synthesis and cysteine availability, which are essential for ferroptosis resistance in some cells.
Conclusion
Transsulfuration (GO:0019346) is a fundamental metabolic pathway that interconverts homocysteine and cysteine, impacting redox balance, neuromodulation, and cell survival. Its dysregulation is implicated in diverse diseases, from neurodegeneration to cancer, making it a compelling target for research. CRISPR-based models and multi-omics approaches are powerful tools to dissect the causal roles of transsulfuration genes and to develop targeted interventions.
References
- 1. Corona-Trejo A et al.. 2023. Transsulfuration pathway: a targeting neuromodulator in Parkinson's disease.. Rev Neurosci 34(8):915-932 PMID: 37409540
- 2. Zhang HF et al.. 2022. Transsulfuration, minor player or crucial for cysteine homeostasis in cancer.. Trends Cell Biol 32(9):800-814 PMID: 35365367
- 3. Sbodio JI et al.. 2019. Regulators of the transsulfuration pathway.. Br J Pharmacol 176(4):583-593 PMID: 30007014
- 4. Mangoni AA et al.. 2024. Transsulfuration and folate pathways in rheumatoid arthritis: A systematic review and meta-analysis.. Eur J Clin Invest 54(4):e14158 PMID: 38214126
- 5. Berry T et al.. 2020. Treatment-resistant schizophrenia: focus on the transsulfuration pathway.. Rev Neurosci 31(2):219-232 PMID: 31714892
- 6. Flori L et al.. 2025. Transsulfuration Pathway Products and H(2)S-Donors in Hyperhomocysteinemia: Potential Strategies Beyond Folic Acid.. Int J Mol Sci 26(13) PMID: 40650206
- 7. Zinellu A et al.. 2023. Arginine, Transsulfuration, and Folic Acid Pathway Metabolomics in Chronic Obstructive Pulmonary Disease: A Systematic Review and Meta-Analysis.. Cells 12(17) PMID: 37681911
- 8. Oberkersch RE et al.. 2025. Transsulfuration metabolism is essential for ferroptosis resistance in quiescent endothelial cells.. Cell Death Dis 17(1):107 PMID: 41422256
