GO:0047150 betaine-homocysteine S-methyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0047150 describes the enzymatic activity that converts homocysteine and glycine betaine into methionine and N,N-dimethylglycine, a key reaction in the methionine cycle.
• Betaine-homocysteine S-methyltransferase (BHMT) is the primary enzyme carrying this activity, and its expression is regulated by S-adenosylmethionine and methylthioadenosine.
• BHMT also localizes to the nucleus, where it contributes to a nuclear methionine cycle, expanding its role beyond cytoplasmic homocysteine regulation.
• BHMT2, a related enzyme, uses S-methylmethionine rather than betaine as a methyl donor, indicating distinct substrate specificity within the family.
• Dietary factors such as egg protein and choline supply can modulate hepatic BHMT activity, linking nutrition to homocysteine homeostasis.
• Dysregulation of BHMT activity is implicated in hepatic steatosis, hyperhomocysteinemia, and related metabolic disorders.
Description
Betaine-homocysteine S-methyltransferase activity (GO:0047150) is a molecular function that catalyzes the transfer of a methyl group from glycine betaine to L-homocysteine, yielding L-methionine and N,N-dimethylglycine. This reaction is a central component of the methionine cycle and provides an alternative pathway for homocysteine remethylation, independent of folate and vitamin B12. Researchers study this activity to understand how cells maintain methionine homeostasis, regulate methylation reactions, and respond to nutritional and metabolic stress. The enzyme responsible, betaine-homocysteine S-methyltransferase (BHMT), is highly expressed in liver and kidney but also found in other tissues, and its activity is tightly controlled by metabolites such as S-adenosylmethionine (SAM) and methylthioadenosine (MTA). Beyond its classical cytoplasmic role, BHMT has been detected in the nucleus, where it participates in a nuclear methionine cycle that may influence epigenetic processes. Recent studies have linked BHMT activity to hepatic steatosis, showing that activation of BHMT1 by ribosomal modification protein rimK-like family member A ameliorates lipid accumulation in the liver. Dietary interventions, such as egg protein supplementation, can upregulate hepatic BHMT activity and prevent hyperhomocysteinemia in folate-restricted rats. In dairy cows, choline supply during negative energy balance alters BHMT and methionine synthase activities, highlighting the sensitivity of this pathway to nutritional status. These findings underscore the importance of GO:0047150 in metabolic health and disease.
betaine-homocysteine S-methyltransferase activity At A Glance
| GO ID | GO:0047150 |
|---|---|
| GO term | betaine-homocysteine S-methyltransferase activity |
| Ontology | molecular_function |
| Synonym | betaine-homocysteine methyltransferase activity; betaine-homocysteine transmethylase activity; trimethylammonioacetate:L-homocysteine S-methyltransferase activity |
| Major function | Catalyzes the transfer of a methyl group from glycine betaine to L-homocysteine, producing L-methionine and N,N-dimethylglycine |
| Reaction | L-homocysteine + glycine betaine = N,N-dimethylglycine + L-methionine |
| Primary enzyme | Betaine-homocysteine S-methyltransferase (BHMT) |
| Related enzyme | BHMT2, which uses S-methylmethionine as a methyl donor |
| Subcellular localization | Cytoplasm and nucleus |
What Is GO:0047150?
GO:0047150 is defined as the catalysis of the reaction: L-homocysteine + glycine betaine = N,N-dimethylglycine + L-methionine. In other words, it is the enzymatic activity that uses betaine as a methyl donor to convert homocysteine into methionine, a critical step in the methionine cycle.
Why Is betaine-homocysteine S-methyltransferase activity Important in Cell Biology?
GO:0047150 is essential for maintaining methionine homeostasis and regulating homocysteine levels, which are critical for cellular methylation reactions, protein synthesis, and redox balance. Dysregulation of this activity is associated with hyperhomocysteinemia, a risk factor for cardiovascular disease, and with hepatic steatosis, where BHMT activation can reduce lipid accumulation. The nuclear presence of BHMT suggests a role in epigenetic regulation through the nuclear methionine cycle. Understanding this activity provides insights into nutritional interventions and potential therapeutic targets for metabolic disorders.
• Maintains methionine levels for protein synthesis and methylation reactions.
• Provides an alternative route for homocysteine remethylation, independent of folate and vitamin B12.
• Regulates homocysteine levels; elevated homocysteine is a risk factor for cardiovascular disease.
• Involved in hepatic lipid metabolism; BHMT activation ameliorates hepatic steatosis.
• Contributes to a nuclear methionine cycle that may influence gene expression.
• Sensitive to nutritional status, including dietary protein and choline supply.
• Regulated by SAM and MTA, linking its activity to cellular methylation potential.
• BHMT2 expands the family with different substrate specificity, suggesting diverse metabolic roles.
What Happens During betaine-homocysteine S-methyltransferase activity?
Substrate binding and methyl transfer
In simple terms: The enzyme grabs a homocysteine molecule and a betaine molecule, then hands over a methyl group from betaine to homocysteine.
The catalytic mechanism of BHMT involves the binding of L-homocysteine and glycine betaine in the active site. The enzyme facilitates the transfer of a methyl group from betaine to homocysteine, producing methionine and dimethylglycine. This reaction is a ping-pong bi-bi mechanism, where betaine binds first and donates its methyl group, followed by the release of dimethylglycine and subsequent binding of homocysteine.
Role in the methionine cycle
In simple terms: This reaction is part of a cycle that recycles homocysteine back into methionine, keeping the cell's methylation machinery running.
The methionine cycle is crucial for supplying methyl groups for various methylation reactions, including DNA and protein methylation. BHMT provides an alternative to the folate-dependent remethylation pathway, using betaine as a methyl donor. This is particularly important in tissues with high betaine availability, such as liver and kidney.
Nuclear methionine cycle
In simple terms: BHMT also works inside the nucleus, where it may help control gene activity by affecting methylation.
BHMT has been found in the nucleus, where it participates in a nuclear methionine cycle. This nuclear pool of methionine may be used for methylation of histones and other nuclear proteins, thereby influencing gene expression. The nuclear localization suggests a specialized role in epigenetic regulation.
Regulation by metabolites
In simple terms: The enzyme's activity can be turned up or down by molecules like SAM and MTA, which reflect the cell's methylation status.
S-adenosylmethionine (SAM) and methylthioadenosine (MTA) inhibit BHMT expression. This feedback regulation ensures that methionine levels are maintained within a narrow range, preventing hyperhomocysteinemia or excessive methylation.
Alternative substrates and BHMT2
In simple terms: A related enzyme, BHMT2, can use a different methyl donor, showing that the family has diverse roles.
BHMT2 is an S-methylmethionine-homocysteine methyltransferase, meaning it uses S-methylmethionine instead of betaine as a methyl donor. This broadens the range of methyl donors that can be used for homocysteine remethylation, potentially providing metabolic flexibility.
Key Genes Involved in GO:0047150 betaine-homocysteine S-methyltransferase activity
The following genes and proteins are directly involved in or regulate betaine-homocysteine S-methyltransferase activity (GO:0047150).
| Gene | Major Role | Research Relevance |
|---|---|---|
| BHMT | Primary enzyme catalyzing the reaction | Central to methionine cycle and homocysteine regulation |
| BHMT2 | Related enzyme using S-methylmethionine as methyl donor | Expands substrate specificity within the family |
| RIMKLA | Activates BHMT1 to ameliorate hepatic steatosis | Potential therapeutic target for fatty liver disease |
| MAT1A | Synthesizes SAM, which regulates BHMT expression | Links methionine metabolism to BHMT regulation |
| GNMT | Glycine N-methyltransferase, affects SAM/SAH ratio | Indirectly influences BHMT activity through methyl balance |
| MTR | Methionine synthase, alternative homocysteine remethylation | Compensatory pathway when BHMT is impaired |
| MTHFR | Folate cycle enzyme, affects homocysteine levels | Interacts with BHMT pathway in homocysteine homeostasis |
| CBS | Transsulfuration enzyme, removes homocysteine | Balances homocysteine disposal with BHMT |
| PEMT | Phosphatidylethanolamine N-methyltransferase, consumes SAM | Affects SAM levels and thus BHMT regulation |
| DNMT1 | DNA methyltransferase, uses SAM | Nuclear methionine cycle may supply SAM for DNMT1 |
| H3K4me3 | Histone methylation mark | Nuclear BHMT may influence histone methylation |
| SLC6A20 | Betaine transporter | Regulates betaine availability for BHMT |
| CHDH | Choline dehydrogenase, produces betaine | Supplies betaine for BHMT reaction |
| ALDH7A1 | Betaine aldehyde dehydrogenase, produces betaine | Alternative betaine synthesis route |
| AHCY | S-adenosylhomocysteine hydrolase | Recycles SAH to homocysteine, affecting BHMT substrate |
| MTRR | Methionine synthase reductase | Supports methionine synthase, interacts with BHMT pathway |
| BHMT1 | Isoform of BHMT | Target of RIMKLA activation in hepatic steatosis |
How Is betaine-homocysteine S-methyltransferase activity Regulated?
BHMT expression is inhibited by S-adenosylmethionine (SAM) and methylthioadenosine (MTA), providing feedback regulation based on cellular methylation status. Dietary factors, such as egg protein and choline, can upregulate hepatic BHMT activity, linking nutrition to homocysteine metabolism. Additionally, RIMKLA activates BHMT1 to ameliorate hepatic steatosis, indicating post-translational regulation.
betaine-homocysteine S-methyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| BHMT | Hepatic steatosis | Liver-specific BHMT knockout or overexpression in mice |
| BHMT | Hyperhomocysteinemia | Folate-restricted rat model with dietary intervention |
| BHMT | Metabolic disorders in dairy cows | Holstein cows during negative energy balance |
| BHMT2 | Methionine cycle flexibility | BHMT2 knockout cell lines |
| RIMKLA | Hepatic steatosis | RIMKLA overexpression in hepatocytes |
Hepatic steatosis
BHMT activity is linked to hepatic lipid metabolism. Activation of BHMT1 by RIMKLA reduces hepatic steatosis, suggesting that enhancing BHMT activity could be therapeutic for fatty liver disease. The correction notice confirms the validity of these findings.
Hyperhomocysteinemia
Impaired BHMT activity can lead to elevated homocysteine levels, a risk factor for cardiovascular disease. Dietary egg protein prevents hyperhomocysteinemia by upregulating hepatic BHMT activity in folate-restricted rats.
Metabolic disorders in dairy cows
In Holstein cows, negative energy balance and choline supply alter BHMT and methionine synthase activities, affecting methionine cycle intermediates. This highlights the importance of BHMT in metabolic adaptation during lactation.
From betaine-homocysteine S-methyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does BHMT knockout affect homocysteine levels? | BHMT knockout mouse or cell line |
| Does a point mutation in BHMT alter substrate specificity? | Point-mutation knock-in cell model |
| Does BHMT overexpression reduce hepatic steatosis? | BHMT overexpression in liver cells or mice |
| Does nuclear BHMT regulate histone methylation? | Tagged knock-in of BHMT with nuclear localization signal |
| Does RIMKLA activate BHMT1? | RIMKLA overexpression or knockout |
| Does choline supply affect BHMT activity? | Dietary manipulation in dairy cows |
How to Study the betaine-homocysteine S-methyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Enzymatic assay | BHMT catalytic activity | Quantify activity in tissue lysates |
| qRT-PCR | BHMT mRNA levels | Assess regulation by SAM |
| Western blot | BHMT protein levels | Determine expression changes |
| LC-MS/MS | Methionine cycle metabolites | Profile homocysteine, methionine, SAM, SAH |
| Immunofluorescence | Subcellular localization | Detect nuclear BHMT |
| CRISPR knockout | Gene function | Create BHMT-null cells |
| Overexpression | Gain-of-function | Test BHMT effect on steatosis |
| Site-directed mutagenesis | Point mutations | Study catalytic residues |
Enzymatic activity assays
BHMT activity can be measured using radiolabeled betaine or homocysteine, followed by separation of products by HPLC or thin-layer chromatography. This directly quantifies the conversion of homocysteine to methionine.
Expression analysis
Quantitative RT-PCR and Western blotting are used to measure BHMT mRNA and protein levels in tissues or cells under different conditions, such as SAM treatment.
Metabolite profiling
LC-MS/MS can quantify methionine cycle intermediates, including homocysteine, methionine, SAM, and SAH, to assess the impact of BHMT activity on cellular metabolism.
Subcellular localization
Immunofluorescence or subcellular fractionation followed by Western blotting can determine the nuclear versus cytoplasmic distribution of BHMT.
How CRISPR Can Be Used to Study GO:0047150 betaine-homocysteine S-methyltransferase activity
Knockout
CRISPR knockout of BHMT can be used to create cell or animal models to study the consequences of loss of betaine-homocysteine S-methyltransferase activity on homocysteine levels, methionine cycle flux, and hepatic lipid metabolism.
Point Mutation
Introducing point mutations in the BHMT active site via CRISPR can help identify critical residues for catalysis and substrate binding, providing insights into the enzymatic mechanism.
Knock-in
Knock-in of tagged BHMT (e.g., GFP or FLAG) allows for tracking its subcellular localization and interaction partners, particularly to study its nuclear role.
Overexpression
Overexpression of BHMT using CRISPR activation or lentiviral delivery can test whether increased activity protects against hyperhomocysteinemia or hepatic steatosis.
How EDITGENE Supports betaine-homocysteine S-methyltransferase activity Research
Researchers studying betaine-homocysteine S-methyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in metabolic pathways, disease phenotypes, or drug responses. EDITGENE provides comprehensive CRISPR-based services to accelerate this research.
Contact EDITGENE today to design your custom CRISPR model for betaine-homocysteine S-methyltransferase activity research.
Frequently Asked Questions About betaine-homocysteine S-methyltransferase activity
What is betaine-homocysteine S-methyltransferase activity?
It is the enzymatic activity (GO:0047150) that catalyzes the conversion of homocysteine and glycine betaine to methionine and N,N-dimethylglycine, a key reaction in the methionine cycle.
What genes are involved in betaine-homocysteine S-methyltransferase activity?
The primary gene is BHMT, which encodes the enzyme. BHMT2 is a related gene with different substrate specificity.
What is the role of BHMT in the methionine cycle?
BHMT provides an alternative pathway for homocysteine remethylation using betaine, helping maintain methionine levels and cellular methylation capacity.
How is BHMT activity regulated?
BHMT expression is inhibited by S-adenosylmethionine and methylthioadenosine, and its activity can be modulated by dietary factors such as egg protein and choline.
What diseases are associated with BHMT dysfunction?
BHMT dysfunction is linked to hyperhomocysteinemia, hepatic steatosis, and metabolic disorders.
Does BHMT have a nuclear function?
Yes, BHMT is present in the nucleus and participates in a nuclear methionine cycle, potentially influencing epigenetic regulation.
What is the difference between BHMT and BHMT2?
BHMT uses glycine betaine as a methyl donor, while BHMT2 uses S-methylmethionine, indicating different substrate specificities.
Can diet affect BHMT activity?
Yes, dietary egg protein upregulates hepatic BHMT activity in folate-restricted rats, and choline supply alters BHMT activity in dairy cows.
How can I study BHMT activity in the lab?
Common methods include enzymatic assays, qRT-PCR, Western blot, and LC-MS/MS for metabolite profiling.
What CRISPR models are available for BHMT research?
EDITGENE provides knockout, point mutation, knock-in, and overexpression models for BHMT and related genes.
Conclusion
Betaine-homocysteine S-methyltransferase activity (GO:0047150) is a critical enzymatic function in the methionine cycle, with far-reaching implications for metabolic health and disease. Understanding its regulation and role in conditions such as hepatic steatosis and hyperhomocysteinemia offers potential for therapeutic intervention. EDITGENE's CRISPR services empower researchers to dissect this pathway with precision.
References
- 1. Yan H et al.. 2024. Ribosomal modification protein rimK-like family member A activates betaine-homocysteine S-methyltransferase 1 to ameliorate hepatic steatosis.. Signal Transduct Target Ther 9(1):214 PMID: 39117631
- 2. Yan H et al.. 2024. Correction: Ribosomal modification protein rimK-like family member A activates betaine-homocysteine S-methyltransferase 1 to ameliorate hepatic steatosis.. Signal Transduct Target Ther 9(1):360 PMID: 39663370
- 3. Szegedi SS et al.. 2008. Betaine-homocysteine S-methyltransferase-2 is an S-methylmethionine-homocysteine methyltransferase.. J Biol Chem 283(14):8939-45 PMID: 18230605
- 4. Pérez-Miguelsanz J et al.. 2017. Betaine homocysteine S-methyltransferase emerges as a new player of the nuclear methionine cycle.. Biochim Biophys Acta Mol Cell Res 1864(7):1165-1182 PMID: 28288879
- 5. Pajares MA et al.. 2006. Betaine homocysteine S-methyltransferase: just a regulator of homocysteine metabolism?. Cell Mol Life Sci 63(23):2792-803 PMID: 17086380
- 6. Ou X et al.. 2007. Inhibition of human betaine-homocysteine methyltransferase expression by S-adenosylmethionine and methylthioadenosine.. Biochem J 401(1):87-96 PMID: 16953798
- 7. Saande CJ et al.. 2019. Dietary Egg Protein Prevents Hyperhomocysteinemia via Upregulation of Hepatic Betaine-Homocysteine S-Methyltransferase Activity in Folate-Restricted Rats.. J Nutr 149(8):1369-1376 PMID: 31111947
- 8. Coleman DN et al.. 2019. Hepatic betaine-homocysteine methyltransferase and methionine synthase activity and intermediates of the methionine cycle are altered by choline supply during negative energy balance in Holstein cows.. J Dairy Sci 102(9):8305-8318 PMID: 31301838
