GO:0044540 L-cystine L-cysteine-lyase (deaminating) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0044540 describes the molecular function that catalyzes the reaction L-cystine + H2O = S-sulfanyl-L-cysteine + pyruvate + NH4+.
• This activity is a deaminating lyase that breaks down L-cystine, a sulfur-containing amino acid, into S-sulfanyl-L-cysteine, pyruvate, and ammonium.
• The reaction is part of cysteine and methionine metabolism and contributes to sulfur amino acid catabolism in cells.
• Enzymes with this activity may influence redox balance because L-cystine and its products affect glutathione and cysteine pools.
• Research on this activity uses biochemical assays, enzyme kinetics, and structural biology to understand its catalytic mechanism.
• CRISPR-based models can help determine whether candidate genes encoding this activity are causally involved in metabolic and disease phenotypes.
Description
GO:0044540, L-cystine L-cysteine-lyase (deaminating) activity, is a molecular function defined by the catalytic reaction L-cystine + H2O = S-sulfanyl-L-cysteine + pyruvate + NH4+. This activity belongs to the class of lyases that remove ammonia from sulfur-containing amino acids, and it is part of the broader network of cysteine and methionine metabolism. Researchers study this term because it sits at the intersection of amino acid catabolism, sulfur trafficking, and redox regulation, processes that influence cell growth and stress responses. The reaction product S-sulfanyl-L-cysteine is a reactive persulfide species that can modify protein thiols and affect cellular redox homeostasis. Pyruvate and ammonium are common metabolic intermediates, linking this activity to central carbon and nitrogen metabolism. Because L-cystine is a major extracellular source of cysteine, enzymes with this activity may modulate the availability of cysteine for glutathione synthesis and protein synthesis. In biomedical research, this GO term is relevant to understanding how cells manage sulfur amino acid stress and how dysregulation of these pathways contributes to disease.
L-cystine L-cysteine-lyase (deaminating) activity At A Glance
| GO ID | GO:0044540 |
|---|---|
| GO term | L-cystine L-cysteine-lyase (deaminating) activity |
| Ontology | molecular_function |
| Synonym | None listed in QuickGO |
| Definition | Catalysis of the reaction: L-cystine + H2O = S-sulfanyl-L-cysteine + pyruvate + NH4+ |
| Major function | Deaminating lyase activity that breaks down L-cystine into S-sulfanyl-L-cysteine, pyruvate, and ammonium |
| Reaction direction | Forward reaction consumes L-cystine and water; produces S-sulfanyl-L-cysteine, pyruvate, and NH4+ |
| Related pathways | Cysteine and methionine metabolism; sulfur amino acid catabolism |
| Substrate | L-cystine |
| Products | S-sulfanyl-L-cysteine, pyruvate, ammonium |
What Is GO:0044540?
In simple terms, GO:0044540 is the enzyme activity that breaks down L-cystine by removing ammonia and producing S-sulfanyl-L-cysteine, pyruvate, and ammonium. The official definition is: Catalysis of the reaction: L-cystine + H2O = S-sulfanyl-L-cysteine + pyruvate + NH4+. This is a deaminating lyase activity, meaning it cleaves a carbon-sulfur bond in L-cystine while releasing ammonia. The reaction consumes water and generates three products, making it a hydrolytic deamination. This activity is distinct from other cysteine-degrading enzymes because it specifically uses L-cystine as a substrate and produces a persulfide product.
Why Is L-cystine L-cysteine-lyase (deaminating) activity Important in Cell Biology?
GO:0044540 is important because it represents a specific enzymatic step in sulfur amino acid catabolism that can influence cellular redox balance, cysteine availability, and glutathione synthesis. Dysregulation of cysteine and methionine metabolism has been linked to metabolic stress, neurodegeneration, and cancer, making this activity a potential target for research into these conditions. Understanding this activity also helps interpret metabolic flux data and design experiments that test causal roles of candidate genes in disease models.
• Contributes to cysteine and methionine metabolism by breaking down L-cystine.
• Produces S-sulfanyl-L-cysteine, a reactive persulfide that can modify protein thiols.
• Links sulfur amino acid catabolism to pyruvate and ammonium production.
• May affect glutathione levels by altering cysteine availability.
• Relevant to redox regulation and oxidative stress responses.
• Provides a biochemical marker for metabolic reprogramming in disease.
• Can be studied using enzyme kinetics and structural biology.
• Serves as a target for CRISPR-based functional validation.
• Helps interpret metabolomic and proteomic data in sulfur metabolism research.
• Potential relevance to neurodegeneration and cancer metabolism.
Molecular Mechanism of L-cystine L-cysteine-lyase (deaminating) activity
Substrate recognition and binding
In simple terms: The enzyme first grabs L-cystine and holds it in place.
The enzyme binds L-cystine, a dimer of cysteine linked by a disulfide bond, through specific interactions that position the substrate for catalysis. This binding step is essential for selectivity, as the enzyme must distinguish L-cystine from other amino acids. Structural studies of related lyases suggest that substrate binding involves conserved residues that coordinate the amino and carboxyl groups of the amino acid.
Catalytic cleavage and deamination
In simple terms: The enzyme cuts the L-cystine molecule and removes ammonia.
Following binding, the enzyme catalyzes a hydrolytic cleavage of L-cystine, resulting in the formation of S-sulfanyl-L-cysteine, pyruvate, and ammonium. This step involves the removal of an amino group (deamination) and the breaking of a carbon-sulfur bond. The reaction consumes water, classifying it as a hydrolytic deamination. The catalytic mechanism likely involves acid-base chemistry and possibly a cofactor, as seen in other deaminating lyases.
Product release and redox implications
In simple terms: The products are released, and one of them can affect the cell's redox state.
After catalysis, S-sulfanyl-L-cysteine, pyruvate, and ammonium are released from the active site. S-sulfanyl-L-cysteine is a persulfide that can participate in thiol-disulfide exchange reactions, potentially modifying protein cysteine residues and influencing redox signaling. Pyruvate and ammonium enter central metabolism, linking this activity to energy production and nitrogen balance.
Cofactors and regulation
In simple terms: The enzyme may need helper molecules and can be turned on or off.
Some deaminating lyases require pyridoxal phosphate (PLP) as a cofactor, but the specific cofactor for GO:0044540 is not explicitly stated in the provided QuickGO definition. Regulation may occur at the transcriptional level or through post-translational modifications, as seen in other metabolic enzymes. The activity could also be influenced by the availability of L-cystine and the redox state of the cell.
Key Genes Involved in GO:0044540 L-cystine L-cysteine-lyase (deaminating) activity
The following genes and proteins are associated with L-cystine L-cysteine-lyase (deaminating) activity or related sulfur amino acid metabolism, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CTH | Cystathionine gamma-lyase, involved in cysteine metabolism | Studied for its role in sulfur amino acid catabolism |
| CBS | Cystathionine beta-synthase, contributes to cysteine synthesis | Linked to metabolic disorders and redox balance |
| MPST | Mercaptopyruvate sulfurtransferase, produces persulfides | Relevant to S-sulfanyl-L-cysteine formation |
| GOT1 | Glutamate oxaloacetate transaminase, links amino acid metabolism | May influence pyruvate and ammonium levels |
| GOT2 | Mitochondrial transaminase, involved in nitrogen metabolism | Potential cross-talk with deamination pathways |
| GLS | Glutaminase, produces glutamate for transamination | Affects ammonium production |
| GLUD1 | Glutamate dehydrogenase, releases ammonium | Connects to nitrogen metabolism |
| SLC7A11 | Cystine/glutamate antiporter, imports cystine | Regulates substrate availability for the activity |
| SLC3A2 | Partner of SLC7A11 for cystine transport | Influences intracellular L-cystine levels |
| GCLC | Glutamate-cysteine ligase, glutathione synthesis | Cysteine availability affects glutathione |
| GCLM | Modulatory subunit of GCLC | Redox regulation linked to cysteine |
| GSR | Glutathione reductase, maintains reduced glutathione | Redox balance influenced by cysteine |
| TXN | Thioredoxin, redox regulation | Persulfides can modify thioredoxin |
| TXN2 | Mitochondrial thioredoxin | May interact with S-sulfanyl-L-cysteine |
| PRDX1 | Peroxiredoxin, antioxidant enzyme | Redox-sensitive and may be affected by persulfides |
| NFE2L2 | Nrf2, transcription factor for antioxidant response | Regulates genes in cysteine metabolism |
| ATF4 | Stress-responsive transcription factor | Coordinates amino acid metabolism |
How Is L-cystine L-cysteine-lyase (deaminating) activity Regulated?
The activity of L-cystine L-cysteine-lyase (deaminating) is likely regulated by substrate availability, redox state, and transcriptional programs that control sulfur amino acid metabolism. For example, the transcription factor NFE2L2 (Nrf2) regulates antioxidant genes and can influence cysteine metabolism. Additionally, ATF4 is activated under amino acid stress and can upregulate genes involved in amino acid catabolism. Post-translational modifications such as oxidation of active-site cysteines may also modulate enzyme activity.
L-cystine L-cysteine-lyase (deaminating) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CTH | Cystathioninuria; redox imbalance | Knockout cell model |
| SLC7A11 | Cancer; ferroptosis sensitivity | Overexpression and knockout models |
| NFE2L2 | Cancer; antioxidant response | Point mutation models |
| MPST | Neurodegeneration; persulfide signaling | Knock-in reporter models |
| GCLC | Oxidative stress; glutathione deficiency | Knockout models |
Cancer metabolism
Altered cysteine and methionine metabolism is a hallmark of cancer, and enzymes involved in L-cystine catabolism may support tumor growth by providing cysteine for glutathione synthesis. Targeting this activity could disrupt redox balance in cancer cells.
Neurodegeneration
Dysregulation of sulfur amino acid metabolism has been implicated in neurodegenerative conditions, where oxidative stress and excitotoxicity contribute to neuronal death. Modulating L-cystine catabolism may affect neuronal redox status.
Metabolic disorders
Inborn errors of sulfur amino acid metabolism, such as cystathioninuria, highlight the importance of these pathways. Although direct mutations in GO:0044540-associated genes are not well defined, the activity is part of a network that can influence metabolic homeostasis.
From L-cystine L-cysteine-lyase (deaminating) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of candidate gene reduce L-cystine lyase activity? | Knockout cell line |
| Does a specific point mutation alter catalytic efficiency? | Point mutation knock-in |
| Can a tagged version track enzyme localization? | Tagged knock-in |
| Does overexpression increase persulfide production? | Overexpression cell line |
| Which genes regulate L-cystine metabolism? | CRISPR library screening |
| What is the metabolic flux through this pathway? | Metabolomics with isotope tracing |
How to Study the L-cystine L-cysteine-lyase (deaminating) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Enzyme kinetics | Catalytic rate and substrate affinity | Characterizing wild-type and mutant enzymes |
| X-ray crystallography | Three-dimensional structure | Active site mapping |
| LC-MS metabolomics | Levels of L-cystine and products | Pathway flux analysis |
| CRISPR knockout screening | Gene essentiality and pathway regulators | Identifying novel components |
| Western blot | Protein expression levels | Validating knockout or overexpression |
| RNA-seq | Transcriptional changes | Pathway regulation |
| Seahorse assay | Mitochondrial respiration | Metabolic impact |
Enzyme activity assays
Biochemical assays measure the conversion of L-cystine to S-sulfanyl-L-cysteine, pyruvate, and ammonium using spectrophotometric or chromatographic methods. These assays can determine kinetic parameters and substrate specificity.
Structural biology
X-ray crystallography and cryo-EM can reveal the active site architecture and substrate binding of enzymes with this activity, as demonstrated for related lyases. Structural insights guide mutagenesis studies.
Metabolomics and flux analysis
Mass spectrometry-based metabolomics quantifies L-cystine, cysteine, and related metabolites in cells and tissues. Isotope tracing can measure flux through the deaminating lyase reaction.
CRISPR screening
Genome-wide CRISPR knockout screens can identify genes that modulate L-cystine catabolism or sensitivity to oxidative stress. Hits can be validated with targeted knockouts.
How CRISPR Can Be Used to Study GO:0044540 L-cystine L-cysteine-lyase (deaminating) activity
Knockout
CRISPR knockout of candidate genes can abolish L-cystine L-cysteine-lyase (deaminating) activity, allowing researchers to test its role in cysteine metabolism and redox balance. Knockout cell lines are valuable for metabolic assays and drug sensitivity studies.
Point Mutation
Introducing specific point mutations in the active site can dissect catalytic residues and determine their contribution to substrate binding and turnover. Point mutation models help validate structural predictions.
Knock-in
Knock-in of tagged versions of the enzyme enables localization and interaction studies using fluorescence or affinity purification. This approach can reveal dynamic changes in enzyme abundance and post-translational modifications.
Overexpression
Overexpression of the enzyme can increase flux through the deaminating lyase reaction, leading to elevated persulfide production and altered redox state. Overexpression models are useful for testing gain-of-function phenotypes.
How EDITGENE Supports L-cystine L-cysteine-lyase (deaminating) activity Research
Researchers studying L-cystine L-cysteine-lyase (deaminating) activity-related genes often need to determine whether a candidate gene is causally involved in metabolic or disease phenotypes. EDITGENE provides CRISPR-based cell model services to enable such functional validation.
Contact EDITGENE today to design your custom CRISPR model for L-cystine L-cysteine-lyase (deaminating) activity research.
Frequently Asked Questions About L-cystine L-cysteine-lyase (deaminating) activity
What is GO:0044540?
GO:0044540 is the molecular function L-cystine L-cysteine-lyase (deaminating) activity, which catalyzes the reaction L-cystine + H2O = S-sulfanyl-L-cysteine + pyruvate + NH4+.
What genes are involved in L-cystine L-cysteine-lyase (deaminating) activity?
Genes such as CTH, CBS, MPST, and SLC7A11 are involved in related sulfur amino acid metabolism and can influence this activity.
What is the substrate of L-cystine L-cysteine-lyase (deaminating) activity?
The substrate is L-cystine, a disulfide-linked dimer of cysteine.
What products are formed by this activity?
The products are S-sulfanyl-L-cysteine, pyruvate, and ammonium.
How is this activity measured in the lab?
It can be measured using enzyme assays that detect product formation, such as pyruvate or ammonium release, or by LC-MS.
Is L-cystine L-cysteine-lyase (deaminating) activity involved in disease?
It is part of sulfur amino acid metabolism, which is implicated in cancer, neurodegeneration, and metabolic disorders.
What cofactors are required for this activity?
The specific cofactor is not stated in the QuickGO definition, but related lyases often use pyridoxal phosphate.
Can CRISPR be used to study this activity?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models can be used to study the function of genes associated with this activity.
What pathways is this activity part of?
It is part of cysteine and methionine metabolism and sulfur amino acid catabolism.
How does this activity affect redox balance?
It produces S-sulfanyl-L-cysteine, a persulfide that can modify protein thiols and influence redox signaling.
Conclusion
GO:0044540, L-cystine L-cysteine-lyase (deaminating) activity, is a specific enzymatic function in sulfur amino acid metabolism that produces a reactive persulfide and links to redox regulation. Understanding its mechanism and regulation can provide insights into metabolic diseases and cancer. CRISPR-based models offer powerful tools to dissect the causal roles of associated genes and to develop targeted research strategies.
References
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