GO:0047127 thiomorpholine-carboxylate dehydrogenase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0047127 describes thiomorpholine-carboxylate dehydrogenase activity, the NAD(P)+-dependent oxidation of thiomorpholine-3-carboxylate to 3,4-dehydro-1,4-thiomorpholine-3-carboxylate.
• The enzyme is also known as ketimine reductase and is now widely identified with the protein mu-crystallin (CRYM) in mammalian brain and other tissues.
• It participates in the pipecolate pathway of lysine degradation, linking amino acid catabolism to cerebral osmolyte and thyroid hormone biology.
• The catalytic mechanism involves hydride transfer from the substrate to NAD(P)+, forming a cyclic ketimine product that can be further metabolized.
• Thyroid hormones, particularly T3, bind mu-crystallin and modulate its ketimine reductase activity, connecting the enzyme to thyroid hormone signaling.
• CRISPR-based knockout, point-mutation, knock-in and overexpression models are powerful tools to dissect the physiological roles of this enzyme.
Description
Thiomorpholine-carboxylate dehydrogenase activity (GO:0047127) is a molecular function defined by the catalytic conversion of thiomorpholine-3-carboxylate to 3,4-dehydro-1,4-thiomorpholine-3-carboxylate using NAD(P)+ as an electron acceptor. This activity is synonymous with ketimine reductase, an enzyme historically studied in bovine brain and later identified as the protein mu-crystallin (CRYM) in mammals. The reaction is part of the pipecolate pathway, a route of lysine degradation that produces cyclic ketimines and pipecolic acid in the central nervous system. Researchers are interested in this activity because it bridges amino acid metabolism, thyroid hormone binding, and neurochemical regulation, with potential implications for neurological and metabolic disorders. Understanding its mechanism, regulation, and physiological substrates is essential for interpreting metabolic flux in brain and other tissues.
thiomorpholine-carboxylate dehydrogenase activity At A Glance
| GO ID | GO:0047127 |
|---|---|
| GO term | thiomorpholine-carboxylate dehydrogenase activity |
| Ontology | molecular_function |
| Synonym | ketimine-reducing enzyme; ketimine reductase activity; thiomorpholine-3-carboxylate:NAD(P)+ 5,6-oxidoreductase activity |
| Definition | Catalysis of the reaction: NAD(P)+ + thiomorpholine-3-carboxylate = NAD(P)H + 3,4-dehydro-1,4-thiomorpholine-3-carboxylate. |
| Major function | Oxidation of thiomorpholine-3-carboxylate with concomitant reduction of NAD(P)+; also acts as a ketimine reductase. |
| Cofactor | NAD+ or NADP+ as electron acceptor. |
| Substrate | Thiomorpholine-3-carboxylate (a cyclic ketimine). |
| Product | 3,4-dehydro-1,4-thiomorpholine-3-carboxylate. |
| Associated protein | Mu-crystallin (CRYM) in mammals. |
| Pathway context | Pipecolate pathway of lysine degradation. |
What Is GO:0047127?
Thiomorpholine-carboxylate dehydrogenase activity is the catalysis of the reaction: NAD(P)+ + thiomorpholine-3-carboxylate = NAD(P)H + 3,4-dehydro-1,4-thiomorpholine-3-carboxylate. In this reaction, the enzyme oxidizes the sulfur-containing cyclic amino acid derivative thiomorpholine-3-carboxylate, transferring hydride to NAD+ or NADP+ and generating the corresponding dehydro product. This activity is also referred to as ketimine reductase or ketimine-reducing enzyme, reflecting its ability to reduce cyclic ketimines in the reverse direction.
Why Is thiomorpholine-carboxylate dehydrogenase activity Important in Cell Biology?
Thiomorpholine-carboxylate dehydrogenase activity is important because it represents a key enzymatic step in the pipecolate pathway, a major route of lysine catabolism in the mammalian brain. The enzyme, identified as mu-crystallin, is highly expressed in the central nervous system and is regulated by thyroid hormones, linking metabolic and endocrine signals. Dysregulation of this activity may contribute to neurological conditions and metabolic imbalances, making it a target for research into brain metabolism and thyroid hormone action.
• Provides a route for lysine degradation via the pipecolate pathway in the brain.
• Generates cyclic ketimine intermediates that can serve as signaling molecules or osmolytes.
• Links amino acid metabolism to thyroid hormone binding through mu-crystallin.
• May influence cerebral osmolyte balance and neuroprotection.
• Is a potential biomarker or therapeutic target in neurological disorders.
• Enables studies of enzyme evolution and biocatalyst engineering.
• Connects to redox balance via NAD(P)H production.
• Relevant to understanding thyroid hormone transport and action in the brain.
What Happens During thiomorpholine-carboxylate dehydrogenase activity?
Substrate Binding and Recognition
In simple terms: The enzyme grabs its substrate, thiomorpholine-3-carboxylate, and positions it for reaction.
The enzyme binds thiomorpholine-3-carboxylate, a cyclic sulfur-containing amino acid derivative, in its active site. This substrate is a ketimine, and the enzyme is also known as ketimine reductase, reflecting its ability to reduce such compounds. The binding likely involves interactions with the carboxylate group and the sulfur atom, orienting the substrate for hydride transfer.
Hydride Transfer to NAD(P)+
In simple terms: The enzyme removes a hydride from the substrate and gives it to NAD+ or NADP+.
In the oxidative direction, the enzyme catalyzes the transfer of a hydride from thiomorpholine-3-carboxylate to the nicotinamide ring of NAD(P)+, forming NAD(P)H. This step is characteristic of dehydrogenase activities and is supported by the definition of the reaction. The reverse reaction, reduction of the ketimine, is also catalyzed by the same enzyme, hence the synonym ketimine reductase.
Product Formation and Release
In simple terms: The product, a dehydro compound, is released, and the enzyme is ready for another cycle.
The oxidation product, 3,4-dehydro-1,4-thiomorpholine-3-carboxylate, is released from the active site. This unsaturated cyclic compound can be further metabolized or excreted. The enzyme can then bind another substrate molecule, continuing the catalytic cycle.
Role in the Pipecolate Pathway
In simple terms: This reaction is part of a larger pathway that breaks down lysine in the brain.
Thiomorpholine-carboxylate dehydrogenase activity participates in the pipecolate pathway, which converts lysine to pipecolic acid and related cyclic ketimines. The enzyme helps channel these intermediates toward downstream products, contributing to cerebral lysine catabolism.
Key Genes Involved in GO:0047127 thiomorpholine-carboxylate dehydrogenase activity
The following genes and proteins are associated with thiomorpholine-carboxylate dehydrogenase activity or its pathway context.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CRYM | Encodes mu-crystallin, the mammalian ketimine reductase/thiomorpholine-carboxylate dehydrogenase | Central to studies of thyroid hormone binding and brain metabolism |
| AASS | Alpha-aminoadipic semialdehyde synthase, involved in lysine degradation upstream of pipecolate | Links lysine catabolism to the pipecolate pathway |
| PIPOX | Pipecolate oxidase, converts pipecolate to alpha-aminoadipic semialdehyde | Connects pipecolate pathway to mitochondrial metabolism |
| DHTKD1 | Dehydrogenase E1 and transketolase domain containing 1, involved in alpha-ketoadipate metabolism | May influence flux through lysine degradation |
| GCDH | Glutaryl-CoA dehydrogenase, involved in lysine/tryptophan degradation | Provides context for related dehydrogenases |
| ALDH7A1 | Aldehyde dehydrogenase 7 family member A1, involved in pipecolate pathway | Mutations cause pyridoxine-dependent epilepsy |
| SLC7A1 | Cationic amino acid transporter, may transport lysine | Affects substrate availability |
| SLC3A2 | Amino acid transporter heavy chain | Indirect role in amino acid uptake |
| SLC7A5 | L-type amino acid transporter 1 | May influence lysine transport |
| OAT | Ornithine aminotransferase, related to pipecolate metabolism | Links to proline/ornithine metabolism |
| PRODH | Proline dehydrogenase, related to pipecolate | Provides comparative insights |
| P5CS | Delta-1-pyrroline-5-carboxylate synthase | Involved in proline synthesis |
| PYCR1 | Pyrroline-5-carboxylate reductase 1 | Related to redox metabolism |
| GLS | Glutaminase, provides glutamate for metabolism | Indirect role in amino acid metabolism |
| GLUD1 | Glutamate dehydrogenase 1 | Links to TCA cycle |
| IDH1 | Isocitrate dehydrogenase 1 | Provides NADPH for reductive reactions |
| IDH2 | Isocitrate dehydrogenase 2 | Mitochondrial NADPH source |
| NNT | Nicotinamide nucleotide transhydrogenase | Maintains NADPH/NADP+ balance |
How Is thiomorpholine-carboxylate dehydrogenase activity Regulated?
Thiomorpholine-carboxylate dehydrogenase activity is regulated by thyroid hormones, particularly T3, which bind to mu-crystallin and modulate its catalytic function. The enzyme's activity may also be influenced by the availability of NAD(P)+ and NAD(P)H, as well as by substrate supply from the pipecolate pathway. Additionally, expression of CRYM may be subject to developmental and tissue-specific regulation, with high levels in the brain and other tissues.
thiomorpholine-carboxylate dehydrogenase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CRYM | Thyroid hormone binding and brain metabolism | CRYM knockout mouse, point-mutation knock-in |
| ALDH7A1 | Pyridoxine-dependent epilepsy | Patient-derived iPSCs, CRISPR-corrected lines |
| AASS | Hyperlysinemia | AASS knockout cell lines |
| PIPOX | Pipecolic acidemia | PIPOX knockout models |
| DHTKD1 | Charcot-Marie-Tooth disease | DHTKD1 knockout neurons |
Neurological Disorders and Brain Metabolism
Alterations in the pipecolate pathway and ketimine reductase activity have been linked to neurological conditions. For example, mutations in ALDH7A1, which acts in the same pathway, cause pyridoxine-dependent epilepsy, highlighting the importance of this metabolic route. Dysregulation of mu-crystallin may affect cerebral osmolyte balance and contribute to neuropathology.
Thyroid Hormone-Related Conditions
Mu-crystallin binds thyroid hormones, and its ketimine reductase activity is modulated by T3. This connection suggests that thyroid disorders could impact the enzyme's function, potentially affecting brain development and metabolism.
Metabolic and Neurodevelopmental Implications
The pipecolate pathway intersects with lysine degradation, and disruptions may lead to metabolic imbalances. While direct links to specific diseases are still emerging, the enzyme's role in amino acid catabolism makes it relevant to inborn errors of metabolism and neurodevelopmental disorders.
From thiomorpholine-carboxylate dehydrogenase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the catalytic mechanism of thiomorpholine-carboxylate dehydrogenase? | Recombinant CRYM with point mutations in active site |
| How does loss of CRYM affect brain metabolism? | CRYM knockout mouse or cell lines |
| Does thyroid hormone binding regulate enzyme activity? | Knock-in of thyroid hormone binding mutants |
| What is the subcellular localization of CRYM? | Tagged knock-in with fluorescent protein |
| Can overexpression of CRYM alter pipecolate pathway flux? | CRYM overexpression cell lines |
| What are the downstream metabolites of the reaction? | Metabolomics of knockout vs wild-type cells |
How to Study the thiomorpholine-carboxylate dehydrogenase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Spectrophotometric assay | NAD(P)H production | Enzyme kinetics and inhibitor screening |
| LC-MS metabolomics | Substrate and product levels | Pathway flux analysis |
| Co-immunoprecipitation | Protein interactions | Identifying binding partners |
| X-ray crystallography | 3D structure | Mechanistic studies |
| CRISPR knockout | Gene function | Loss-of-function phenotypes |
| RNA-seq | Transcriptional changes | Pathway regulation |
| Proteomics | Protein abundance | Expression profiling |
Enzymatic Assays
Direct measurement of thiomorpholine-carboxylate dehydrogenase activity can be performed using spectrophotometric assays that monitor NAD(P)H production at 340 nm. Such assays are essential for characterizing kinetic parameters and inhibitor effects.
Metabolomics and Flux Analysis
Metabolomic profiling by mass spectrometry can quantify thiomorpholine-3-carboxylate and its dehydro product, as well as other pipecolate pathway intermediates, in cells and tissues. This approach helps assess pathway flux in response to genetic perturbations.
Protein-Protein Interaction Studies
Co-immunoprecipitation and affinity purification coupled with mass spectrometry can identify interacting partners of mu-crystallin, such as thyroid hormone carriers or other metabolic enzymes.
Structural Biology
X-ray crystallography and cryo-EM can resolve the structure of mu-crystallin bound to NADPH and thyroid hormones, providing insights into substrate binding and catalysis.
How CRISPR Can Be Used to Study GO:0047127 thiomorpholine-carboxylate dehydrogenase activity
Knockout
CRISPR-Cas9 knockout of CRYM can abolish thiomorpholine-carboxylate dehydrogenase activity, allowing researchers to study its role in lysine metabolism and thyroid hormone biology. Knockout cell lines and animal models are valuable for assessing metabolic and neurological phenotypes.
Point Mutation
Introducing point mutations in the active site of CRYM can dissect catalytic residues and cofactor binding. For example, mutating residues involved in hydride transfer can reveal their importance for enzyme activity.
Knock-in
Knock-in of tagged CRYM (e.g., GFP or FLAG) enables visualization and purification of the enzyme, facilitating localization and interaction studies. Knock-in of disease-associated variants can model their effects on enzyme function.
Overexpression
Overexpression of CRYM in cell lines can increase flux through the pipecolate pathway, helping to identify downstream metabolites and physiological consequences. This approach is useful for biochemical characterization and drug screening.
How EDITGENE Supports thiomorpholine-carboxylate dehydrogenase activity Research
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Contact EDITGENE today to design your custom CRISPR model for thiomorpholine-carboxylate dehydrogenase activity research.
Frequently Asked Questions About thiomorpholine-carboxylate dehydrogenase activity
What is thiomorpholine-carboxylate dehydrogenase activity?
It is the enzymatic activity (GO:0047127) that catalyzes the NAD(P)+-dependent oxidation of thiomorpholine-3-carboxylate to 3,4-dehydro-1,4-thiomorpholine-3-carboxylate, also known as ketimine reductase.
What genes are involved in thiomorpholine-carboxylate dehydrogenase activity?
The primary gene is CRYM, which encodes mu-crystallin, the mammalian enzyme with this activity. Other genes in the pipecolate pathway include AASS, PIPOX, and ALDH7A1.
What is the function of mu-crystallin?
Mu-crystallin (CRYM) functions as a ketimine reductase and thiomorpholine-carboxylate dehydrogenase, and it also binds thyroid hormones, linking metabolism to endocrine signaling.
How is thiomorpholine-carboxylate dehydrogenase activity regulated?
It is regulated by thyroid hormones, particularly T3, which bind to mu-crystallin and modulate its activity. Cofactor availability and substrate supply also influence the reaction.
What diseases are associated with thiomorpholine-carboxylate dehydrogenase activity?
Disruptions in the pipecolate pathway, in which this activity participates, have been linked to neurological disorders such as pyridoxine-dependent epilepsy (via ALDH7A1) and potential metabolic imbalances.
What is the pipecolate pathway?
The pipecolate pathway is a route of lysine degradation in the brain that produces pipecolic acid and cyclic ketimines, involving enzymes like thiomorpholine-carboxylate dehydrogenase.
How can I study thiomorpholine-carboxylate dehydrogenase activity in the lab?
You can use enzymatic assays, metabolomics, and CRISPR-based knockout or overexpression models to investigate its function and regulation.
What are the substrates and products of this enzyme?
The substrate is thiomorpholine-3-carboxylate, and the product is 3,4-dehydro-1,4-thiomorpholine-3-carboxylate, with NAD(P)+ as cofactor.
Is thiomorpholine-carboxylate dehydrogenase activity the same as ketimine reductase?
Yes, ketimine reductase is a synonym for this activity, reflecting its ability to reduce cyclic ketimines.
What model systems are available for studying this activity?
CRISPR knockout mice, cell lines, and recombinant protein systems are commonly used, along with patient-derived cells for disease modeling.
Conclusion
Thiomorpholine-carboxylate dehydrogenase activity (GO:0047127) is a key enzymatic function in the pipecolate pathway, catalyzed by mu-crystallin in mammals. Its dual role in lysine metabolism and thyroid hormone binding makes it a fascinating target for neurological and metabolic research. Understanding its mechanism and regulation could shed light on brain metabolism and related disorders.
References
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- 3. Hallen A et al.. 2013. Lysine metabolism in mammalian brain: an update on the importance of recent discoveries.. Amino Acids 45(6):1249-72 PMID: 24043460
- 4. Nardini M et al.. 1988. Bovine brain ketimine reductase.. Biochim Biophys Acta 957(2):286-92 PMID: 3191146
- 5. Borel F et al.. 2014. Crystal structure of mouse mu-crystallin complexed with NADPH and the T3 thyroid hormone.. FEBS J 281(6):1598-612 PMID: 24467707
- 6. Hallen A et al.. 2011. Mammalian forebrain ketimine reductase identified as μ-crystallin; potential regulation by thyroid hormones.. J Neurochem 118(3):379-87 PMID: 21332720
- 7. Hallen A et al.. 2015. Insights into Enzyme Catalysis and Thyroid Hormone Regulation of Cerebral Ketimine Reductase/μ-Crystallin Under Physiological Conditions.. Neurochem Res 40(6):1252-66 PMID: 25931162
- 8. Telek A et al.. 2026. Accessible biocatalyst development by rapid in vitro semi-rational engineering (RISE) of enzymes.. iScience 29(1):114257 PMID: 41550753
