GO:0050667 homocysteine metabolic process: Methionine Cycle, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0050667 homocysteine metabolic process describes the chemical reactions and pathways involving homocysteine, a sulfur-containing amino acid and key intermediate in methionine metabolism.
• Homocysteine sits at the intersection of two major routes: remethylation to methionine and transsulfuration to cysteine.
• Elevated homocysteine (hyperhomocysteinemia) is a pathological metabolic marker linked to cardiovascular disease, psoriasis, and DNA methylation changes.
• The process depends on folate, vitamin B12, vitamin B6, and choline as methyl-donor and cofactor sources.
• Oxidative stress from hyperhomocysteinemia contributes to endothelial dysfunction and atherosclerosis.
• CRISPR-based models (knockout, point mutation, knock-in, overexpression) enable causal dissection of homocysteine metabolic genes in disease.
Description
Homocysteine is a non-proteinogenic amino acid that serves as a critical branch point in one-carbon metabolism. The Gene Ontology term GO:0050667, homocysteine metabolic process, encompasses the chemical reactions and pathways involving homocysteine, including its synthesis from S-adenosylhomocysteine and its utilization in remethylation and transsulfuration. This process is fundamental to cellular methylation capacity, redox balance, and sulfur amino acid homeostasis. Dysregulation of homocysteine metabolism leads to hyperhomocysteinemia, which is recognized as an independent risk factor for cardiovascular disease, stroke, and cognitive decline. The pathological effects of elevated homocysteine include oxidative stress, endothelial injury, and altered DNA methylation patterns. Because homocysteine metabolism intersects with folate, vitamin B12, and choline pathways, nutritional and genetic factors jointly influence its flux. For researchers, GO:0050667 provides a framework to study the enzymes, transporters, and regulatory mechanisms that maintain homocysteine balance. Understanding this process at the molecular level is essential for developing targeted therapies for remethylation disorders, cardiovascular disease, and other metabolic conditions.
homocysteine metabolic process At A Glance
| GO ID | GO:0050667 |
|---|---|
| GO term | homocysteine metabolic process |
| Ontology | biological_process |
| Synonym | Hcy metabolic process; Hcy metabolism; homocysteine metabolism |
| Major function | Maintains methionine and cysteine homeostasis, supports methylation reactions, and controls cellular redox status |
| Key intermediates | Homocysteine, methionine, S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), cysteine |
| Cofactors | Vitamin B12, folate, vitamin B6, choline, betaine |
| Associated diseases | Hyperhomocysteinemia, cardiovascular disease, psoriasis, remethylation disorders |
What Is GO:0050667?
GO:0050667 homocysteine metabolic process is defined as the chemical reactions and pathways involving homocysteine, the amino acid alpha-amino-gamma-mercaptobutanoic acid. Homocysteine is an important intermediate in the metabolic reactions of its S-methyl derivative, methionine. This biological process includes the synthesis of homocysteine from S-adenosylhomocysteine, its remethylation to methionine, and its transsulfuration to cysteine. The term is synonymous with Hcy metabolic process, Hcy metabolism, and homocysteine metabolism.
Why Is homocysteine metabolic process Important in Cell Biology?
Homocysteine metabolic process is critically important because it links nutrient status, methylation capacity, and oxidative stress to human health and disease. Elevated homocysteine is a well-established pathological marker for cardiovascular risk and is associated with endothelial dysfunction, atherosclerosis, and thrombosis. The process also influences DNA methylation and epigenetic regulation, with implications for psoriasis and other inflammatory conditions. Moreover, inherited defects in homocysteine metabolism cause remethylation disorders that require precise diagnosis and management. Studying GO:0050667 helps researchers identify therapeutic targets and biomarkers for these conditions.
• Hyperhomocysteinemia is an independent risk factor for cardiovascular disease, including atherosclerosis and stroke.
• Homocysteine imbalance serves as a pathological metabolic marker in clinical settings.
• The process regulates DNA methylation and epigenetic gene expression through SAM/SAH ratio.
• Oxidative stress from elevated homocysteine contributes to endothelial injury.
• Remethylation disorders caused by genetic defects in homocysteine metabolism require specialized diagnosis and management.
• Nutritional factors such as folate, vitamin B12, and choline directly influence homocysteine flux.
• Homocysteine metabolism is linked to psoriasis and other inflammation-related conditions.
• The transsulfuration pathway connects homocysteine to cysteine and glutathione synthesis, affecting antioxidant defense.
• Genetic variants in enzymes of this pathway modulate disease susceptibility and treatment response.
• CRISPR models enable functional validation of homocysteine-related genes in disease contexts.
What Happens During homocysteine metabolic process?
Synthesis of Homocysteine from S-Adenosylhomocysteine
In simple terms: Homocysteine is made when SAM donates its methyl group and becomes SAH, which is then broken down.
Homocysteine is generated through the hydrolysis of S-adenosylhomocysteine (SAH) by SAH hydrolase (AHCY). SAH is produced when S-adenosylmethionine (SAM) serves as a methyl donor for numerous methylation reactions, including DNA, RNA, protein, and lipid methylation. The ratio of SAM to SAH is a critical indicator of cellular methylation potential, and its alteration affects epigenetic regulation. This step directly links homocysteine metabolism to methyl-donor availability from folate, choline, and betaine.
Remethylation of Homocysteine to Methionine
In simple terms: Homocysteine can be converted back to methionine using methyl groups from folate or betaine.
Homocysteine remethylation to methionine occurs via two main routes. The folate-dependent pathway uses methionine synthase (MTR), which transfers a methyl group from 5-methyltetrahydrofolate to homocysteine, with vitamin B12 as a cofactor. The alternative betaine-dependent pathway uses betaine-homocysteine S-methyltransferase (BHMT), primarily in liver and kidney. Defects in MTR or its cofactor metabolism cause remethylation disorders characterized by hyperhomocysteinemia and neurological symptoms. This step is essential for regenerating methionine and maintaining SAM pools for methylation.
Transsulfuration of Homocysteine to Cysteine
In simple terms: Homocysteine can be converted to cysteine, which is used to make antioxidants like glutathione.
In the transsulfuration pathway, homocysteine condenses with serine to form cystathionine, catalyzed by cystathionine beta-synthase (CBS) with vitamin B6 as a cofactor. Cystathionine is then cleaved by cystathionine gamma-lyase (CTH) to release cysteine and alpha-ketobutyrate. Cysteine is a precursor for glutathione, a major cellular antioxidant, linking homocysteine metabolism to redox defense. This pathway is irreversible and represents the major route for homocysteine disposal when methionine is abundant.
Regulation by Methyl Donors and Cofactors
In simple terms: Vitamins and nutrients control how fast homocysteine is processed.
Homocysteine metabolism is tightly regulated by the availability of methyl donors and cofactors. Folate, vitamin B12, vitamin B6, choline, and betaine are essential nutrients that modulate enzyme activity and pathway flux. SAM acts as an allosteric activator of CBS and an inhibitor of MTHFR, providing feedback regulation. Choline deficiency can impair remethylation and elevate homocysteine. These regulatory mechanisms ensure that homocysteine levels are maintained within a narrow physiological range.
Oxidative Stress and Homocysteine Toxicity
In simple terms: Too much homocysteine causes oxidative damage to cells.
Elevated homocysteine promotes oxidative stress through the generation of reactive oxygen species, including hydrogen peroxide and superoxide. This oxidative stress contributes to endothelial dysfunction, lipid peroxidation, and vascular injury, which are hallmarks of atherosclerosis. Homocysteine also interferes with nitric oxide bioavailability and promotes a prothrombotic state. These mechanisms explain the strong association between hyperhomocysteinemia and cardiovascular disease.
Key Genes Involved in GO:0050667 homocysteine metabolic process
The following genes encode enzymes, transporters, and regulatory proteins that directly participate in or regulate homocysteine metabolic process.
| Gene | Major Role | Research Relevance |
|---|---|---|
| MTHFR | Converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate for remethylation | Common variants affect homocysteine levels and disease risk |
| MTR | Methionine synthase; remethylates homocysteine to methionine using vitamin B12 | Defects cause remethylation disorders |
| MTRR | Methionine synthase reductase; maintains MTR in active reduced state | Required for MTR function; defects cause remethylation disorders |
| BHMT | Betaine-homocysteine S-methyltransferase; alternative remethylation route | Liver-specific; links choline metabolism to homocysteine |
| CBS | Cystathionine beta-synthase; commits homocysteine to transsulfuration | Defects cause classical homocystinuria |
| CTH | Cystathionine gamma-lyase; generates cysteine from cystathionine | Links homocysteine to glutathione synthesis |
| AHCY | S-adenosylhomocysteine hydrolase; produces homocysteine from SAH | Regulates SAM/SAH ratio and methylation potential |
| MAT1A | Methionine adenosyltransferase; synthesizes SAM from methionine | Controls SAM supply for methylation |
| GNMT | Glycine N-methyltransferase; regulates SAM/SAH ratio | Affects homocysteine production |
| SLC19A1 | Folate transporter; uptake of reduced folates | Influences folate availability for remethylation |
| TCN2 | Transcobalamin II; vitamin B12 transport | Affects B12 delivery to MTR |
| FOLR1 | Folate receptor alpha; cellular folate uptake | Modulates folate-dependent remethylation |
| PEMT | Phosphatidylethanolamine N-methyltransferase; consumes SAM | Links choline and homocysteine metabolism |
| CHDH | Choline dehydrogenase; choline oxidation to betaine | Supports betaine-dependent remethylation |
| SLC44A1 | Choline transporter-like protein 1 | Regulates choline availability |
| MMACHC | Cobalamin processing; intracellular B12 metabolism | Defects cause remethylation disorders |
| MMADHC | Cobalamin trafficking; supports MTR cofactor synthesis | Defects cause remethylation disorders |
| LMBRD1 | Lysosomal cobalamin transport | Defects cause remethylation disorders |
How Is homocysteine metabolic process Regulated?
Homocysteine metabolic process is regulated at multiple levels. Allosteric regulation by SAM activates CBS and inhibits MTHFR, balancing remethylation and transsulfuration. Hormonal and nutritional signals, including folate, vitamin B12, and choline status, modulate enzyme expression and activity. Transcriptional regulation of MTHFR, MTR, and CBS responds to cellular one-carbon status. Oxidative stress can also influence enzyme activity and homocysteine export. In remethylation disorders, genetic defects in cobalamin processing or MTR function disrupt this regulation, leading to hyperhomocysteinemia.
homocysteine metabolic process and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MTHFR | Hyperhomocysteinemia, cardiovascular risk | Point mutation knock-in (C677T) in cell lines |
| CBS | Classical homocystinuria, thrombosis | Knockout in hepatocyte-like cells |
| MTR | Remethylation disorder, neurological impairment | Knockout or point mutation in fibroblasts |
| MMACHC | Methylmalonic aciduria and homocystinuria | Knockout in HEK293 or patient iPSCs |
| BHMT | Choline metabolism, liver disease | Overexpression in HepG2 cells |
Cardiovascular Disease and Atherosclerosis
Hyperhomocysteinemia is an independent risk factor for atherosclerosis, stroke, and myocardial infarction. Elevated homocysteine promotes endothelial dysfunction, oxidative stress, and vascular smooth muscle proliferation. The oxidant stress induced by hyperhomocysteinemia contributes to lipid peroxidation and inflammatory signaling in the vessel wall. These mechanisms link homocysteine metabolic process to the pathogenesis of cardiovascular disease.
Remethylation Disorders
Inherited defects in homocysteine remethylation, including MTR, MTRR, MMACHC, and MMADHC deficiencies, cause remethylation disorders characterized by hyperhomocysteinemia, hypomethioninemia, and neurological impairment. These conditions require specialized diagnostic and management guidelines, as recently revised. Early identification and targeted treatment can improve outcomes.
Psoriasis and Inflammatory Conditions
Homocysteine has been proposed as a common route linking cardiovascular risk and DNA methylation in psoriasis. Elevated homocysteine levels in psoriasis patients may contribute to increased cardiovascular comorbidity through methylation changes and oxidative stress. This highlights the broader relevance of homocysteine metabolism in inflammatory skin diseases.
Epigenetic Dysregulation
Homocysteine metabolism influences DNA methylation by controlling the SAM/SAH ratio. Choline and other methyl donors modulate epigenetic marks, and their deficiency can alter gene expression. Hyperhomocysteinemia has been associated with aberrant DNA methylation patterns in various diseases.
From homocysteine metabolic process-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of MTHFR alter homocysteine flux? | MTHFR knockout cell line (e.g., HepG2) |
| Does the C677T variant affect enzyme activity? | MTHFR C677T point mutation knock-in |
| Can CBS rescue hyperhomocysteinemia? | CBS overexpression in hepatocytes |
| How does MTR deficiency affect methylation? | MTR knockout with SAM/SAH measurement |
| Does tagged MTR localize to mitochondria? | MTR GFP knock-in |
| Which genes modify homocysteine levels? | CRISPR library screening in metabolic cell model |
How to Study the homocysteine metabolic process Process
| Method | What It Measures | Typical Application |
|---|---|---|
| LC-MS/MS | Homocysteine, methionine, SAM, SAH levels | Quantify pathway metabolites in cells/tissues |
| Enzyme activity assay | MTHFR, MTR, CBS, BHMT activity | Validate genetic variants |
| Bisulfite sequencing | DNA methylation status | Assess epigenetic effects of homocysteine |
| Stable isotope tracing | Flux through remethylation/transsulfuration | Determine pathway dynamics |
| Western blot | Protein expression of pathway enzymes | Confirm knockout or overexpression |
| CRISPR knockout screen | Genes affecting homocysteine sensitivity | Discover novel regulators |
| RNA-seq | Transcriptional changes | Identify compensatory responses |
| Immunofluorescence | Subcellular localization of enzymes | Study mitochondrial/cytosolic pools |
Metabolite Profiling by LC-MS/MS
Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is the gold standard for quantifying homocysteine, methionine, cysteine, SAM, and SAH in cells and tissues. This method enables precise measurement of flux through remethylation and transsulfuration pathways. Stable isotope tracing can further resolve pathway dynamics.
Enzyme Activity Assays
Enzymatic assays for MTHFR, MTR, CBS, and BHMT activity provide functional readouts of homocysteine metabolism. These assays typically use radiolabeled substrates or spectrophotometric detection. They are essential for validating genetic variants identified in patient cohorts.
DNA Methylation Analysis
Because homocysteine metabolism affects the SAM/SAH ratio, DNA methylation analysis (e.g., bisulfite sequencing, methylation arrays) is used to assess epigenetic consequences. Global and locus-specific methylation changes can be correlated with homocysteine levels.
CRISPR Screening and Functional Genomics
Pooled CRISPR knockout screens can identify genes that modify homocysteine sensitivity or flux in cultured cells. Combined with metabolomics and transcriptomics, these screens reveal novel regulators of GO:0050667. Bioinformatics integration of screen hits with pathway databases prioritizes candidate genes for validation.
How CRISPR Can Be Used to Study GO:0050667 homocysteine metabolic process
Knockout
CRISPR knockout of genes such as MTHFR, MTR, CBS, or BHMT in cell lines (e.g., HepG2, HEK293) creates models to study loss-of-function effects on homocysteine metabolism. These models can be used to measure metabolite levels, enzyme activity, and downstream phenotypes like oxidative stress. Knockout of AHCY or GNMT helps dissect the SAM/SAH regulatory axis.
Point Mutation
Point mutation knock-in models, such as the MTHFR C677T variant, allow researchers to study the functional impact of clinically relevant polymorphisms on enzyme activity and homocysteine levels. These models are valuable for genotype-phenotype correlation and drug response studies.
Knock-in
Knock-in of tagged versions of MTR, CBS, or BHMT (e.g., GFP or HA tags) enables real-time localization and interaction studies in live cells. Knock-in of patient-specific mutations in MMACHC or MMADHC can recapitulate remethylation disorders for mechanistic and therapeutic studies.
Overexpression
Overexpression of CBS or BHMT can rescue hyperhomocysteinemia in cellular models and test whether increased flux through transsulfuration or remethylation is protective. Overexpression of MTHFR or MTR can enhance methylation capacity and alter epigenetic profiles. These models are useful for validating therapeutic targets.
How EDITGENE Supports homocysteine metabolic process Research
Researchers studying homocysteine metabolic process-related genes often need to determine whether a candidate gene is causally involved in metabolite flux, oxidative stress, or disease phenotypes. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models for such functional studies.
Contact EDITGENE today to design your custom CRISPR model for homocysteine metabolic process research.
Frequently Asked Questions About homocysteine metabolic process
What is GO:0050667 homocysteine metabolic process?
GO:0050667 is a Gene Ontology biological process term describing the chemical reactions and pathways involving homocysteine, including its synthesis, remethylation to methionine, and transsulfuration to cysteine.
What genes are involved in homocysteine metabolic process?
Key genes include MTHFR, MTR, MTRR, BHMT, CBS, CTH, AHCY, MAT1A, GNMT, and cobalamin processing genes such as MMACHC and MMADHC.
Why is homocysteine metabolism important?
It maintains methionine and cysteine homeostasis, supports methylation reactions, and controls oxidative stress; dysregulation causes hyperhomocysteinemia linked to cardiovascular disease and remethylation disorders.
What diseases are associated with homocysteine metabolism?
Hyperhomocysteinemia, atherosclerosis, stroke, remethylation disorders, psoriasis, and epigenetic dysregulation are associated with altered homocysteine metabolism.
How is homocysteine metabolized?
Homocysteine is remethylated to methionine via MTR or BHMT, or converted to cysteine via CBS and CTH in the transsulfuration pathway.
What are the symptoms of remethylation disorders?
Remethylation disorders present with hyperhomocysteinemia, hypomethioninemia, neurological impairment, and developmental delay; diagnosis and management follow recent guidelines.
Can CRISPR be used to study homocysteine metabolism?
Yes, CRISPR knockout, point mutation knock-in, and overexpression models enable functional studies of homocysteine-related genes in disease contexts.
What is the role of MTHFR in homocysteine metabolism?
MTHFR converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, providing the methyl group for remethylation of homocysteine to methionine.
How does homocysteine cause cardiovascular disease?
Elevated homocysteine induces oxidative stress, endothelial dysfunction, and promotes atherosclerosis through multiple mechanisms.
What nutrients affect homocysteine levels?
Folate, vitamin B12, vitamin B6, choline, and betaine are key nutrients that modulate homocysteine metabolism.
Conclusion
GO:0050667 homocysteine metabolic process is a central biological pathway that integrates nutrient status, methylation capacity, and redox balance. Its dysregulation is implicated in cardiovascular disease, remethylation disorders, and inflammatory conditions such as psoriasis. Understanding the enzymes, cofactors, and regulatory mechanisms of this process is essential for developing targeted interventions. CRISPR-based cell models provide powerful tools to dissect the causal roles of homocysteine-related genes. By combining knockout, point mutation, knock-in, and overexpression strategies with metabolomics and epigenomics, researchers can accelerate discovery of biomarkers and therapeutics for homocysteine-associated diseases.
References
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