GO:0006534 obsolete cysteine metabolic process: Sulfur Amino Acid Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0006534 (obsolete cysteine metabolic process) is an archived Gene Ontology term that described the chemical reactions and pathways involving cysteine, 2-amino-3-mercaptopropanoic acid.
• The term was made obsolete because cysteine metabolism is now represented by more specific child terms covering transsulfuration, cysteine biosynthesis, and cysteine catabolism.
• Cysteine is a conditionally essential sulfur-containing amino acid central to glutathione synthesis, protein structure, and redox homeostasis.
• Dysregulated cysteine metabolism is implicated in arsenicosis, lens pathology, and age-related T cell dysfunction.
• Key experimental approaches include amino acid adequacy studies, proteolysis assays, and ubiquitin-proteasome pathway analysis.
• Researchers should map obsolete GO:0006534 annotations to current GO terms such as cysteine biosynthetic process (GO:0019344) or cysteine catabolic process (GO:0044273).
Description
GO:0006534, officially named obsolete cysteine metabolic process, is an archived biological_process term in the Gene Ontology that was defined as the chemical reactions and pathways involving cysteine, 2-amino-3-mercaptopropanoic acid. Cysteine is a sulfur-containing amino acid that plays critical roles in protein synthesis, disulfide bond formation, and as a precursor to glutathione, taurine, and hydrogen sulfide. The term was obsoleted because the ontology curators determined that cysteine metabolism is better captured by more granular child terms that distinguish biosynthesis, catabolism, and transsulfuration. Despite its obsolete status, GO:0006534 remains relevant for researchers who encounter legacy annotations in older datasets and need to interpret them correctly. Understanding the historical context of this term helps avoid misannotation and ensures that functional enrichment analyses reflect current ontology standards. This article reviews the definition, biological significance, associated genes, and experimental methods relevant to cysteine metabolism, with a focus on how the obsolete term relates to contemporary research.
obsolete cysteine metabolic process At A Glance
| GO ID | GO:0006534 |
|---|---|
| GO term | obsolete cysteine metabolic process |
| Ontology | biological_process |
| Synonym | cysteine metabolism |
| Definition | OBSOLETE. The chemical reactions and pathways involving cysteine, 2-amino-3-mercaptopropanoic acid. |
| Obsoletion reason | Replaced by more specific child terms for cysteine biosynthesis, catabolism, and transsulfuration. |
| Major function | Historical annotation of cysteine metabolism; now covered by GO:0019344, GO:0044273, and related terms. |
| Related amino acid | Cysteine (2-amino-3-mercaptopropanoic acid), a sulfur-containing, conditionally essential amino acid. |
What Is GO:0006534?
GO:0006534 (obsolete cysteine metabolic process) was defined in the Gene Ontology as the chemical reactions and pathways involving cysteine, 2-amino-3-mercaptopropanoic acid. The synonym cysteine metabolism was also used. This term is now obsolete, meaning it is no longer actively maintained or recommended for annotation. Researchers should instead use current child terms that describe specific aspects of cysteine metabolism, such as cysteine biosynthetic process, cysteine catabolic process, or transsulfuration. The obsoletion reflects the ontology's evolution toward more precise and non-overlapping definitions.
Why Is obsolete cysteine metabolic process Important in Cell Biology?
Although GO:0006534 is obsolete, understanding cysteine metabolism remains critically important because cysteine is a limiting substrate for glutathione synthesis, a key antioxidant defense. Dysregulated cysteine metabolism has been linked to arsenicosis, where arsenic exposure disrupts sulfur amino acid homeostasis. In the lens, proteolysis and ubiquitin-proteasome pathway function are required for normal cell proliferation and differentiation, processes that depend on cysteine availability. Age-related changes in T cell proteodynamics also involve altered amino acid handling, including cysteine. Therefore, researchers studying these pathways must correctly interpret legacy annotations to GO:0006534 and map them to current ontology terms.
• Cysteine is a precursor for glutathione, the major intracellular antioxidant, making its metabolism central to redox balance.
• Arsenicosis involves disruption of sulfur amino acid metabolism, including cysteine pathways.
• Lens cell proliferation and differentiation require ubiquitin-proteasome pathway function, which is sensitive to amino acid availability.
• Proteolysis in the lens is linked to cysteine-dependent enzymes and protein degradation.
• Aging human T cells show altered proteodynamics that may involve cysteine metabolism.
• Cysteine metabolism is relevant to autophagy regulation, as Atg4B is a cysteine protease.
• Bombyx larval fat body destruction involves upregulated proteases that may depend on cysteine.
• N-acetyl cysteine is used in biomedical applications for its antioxidant and mucolytic properties.
• Amino acid adequacy in pathophysiological states often hinges on sulfur amino acid supply.
• Correct mapping of obsolete GO terms prevents misannotation in functional genomics.
What Happens During obsolete cysteine metabolic process?
Historical Definition and Scope
In simple terms: This term used to describe all the chemical steps that build, use, or break down cysteine in cells.
GO:0006534 was created to capture the full set of reactions involving cysteine, including its synthesis from methionine via transsulfuration, its incorporation into proteins, and its catabolism to pyruvate and sulfate. The term was intended to be broad, covering both biosynthetic and degradative pathways. However, as the Gene Ontology matured, curators recognized that this broad definition overlapped with more specific terms, leading to its obsoletion.
Cysteine Biosynthesis (Transsulfuration)
In simple terms: Cells can make cysteine from methionine through a series of reactions called transsulfuration.
In mammals, cysteine is synthesized from the essential amino acid methionine via the transsulfuration pathway, which involves cystathionine beta-synthase and cystathionine gamma-lyase. This pathway is particularly important when dietary cysteine is limiting, as in pathophysiological states. The obsolete term GO:0006534 would have encompassed these reactions, but current annotations use GO:0019344 (cysteine biosynthetic process).
Cysteine Catabolism
In simple terms: When cysteine is broken down, it can be converted into other molecules like pyruvate, sulfate, and taurine.
Cysteine catabolism occurs via multiple routes, including desulfuration to pyruvate and sulfate, and oxidation to taurine. These reactions are critical for sulfur disposal and energy production. The obsolete GO:0006534 covered these degradative steps, but they are now represented by GO:0044273 (cysteine catabolic process).
Role in Protein Synthesis and Folding
In simple terms: Cysteine is used to build proteins and can form disulfide bonds that stabilize protein structure.
Cysteine is incorporated into nascent polypeptides during translation and can form disulfide bonds that are essential for protein folding and stability. Proteolysis and protein quality control pathways, such as the ubiquitin-proteasome system, depend on cysteine availability. In the lens, ubiquitin-proteasome pathway function is required for cell proliferation and differentiation.
Cysteine in Redox Homeostasis and Signaling
In simple terms: Cysteine helps cells manage oxidative stress by serving as a building block for glutathione.
Cysteine is the rate-limiting substrate for glutathione synthesis, a major antioxidant. N-acetyl cysteine, a cysteine derivative, is used in biomedical applications to replenish glutathione and modulate redox signaling. Dysregulation of cysteine metabolism can lead to oxidative stress, which is implicated in aging and disease.
Key Genes Involved in GO:0006534 obsolete cysteine metabolic process
The following genes and proteins are involved in cysteine metabolism and related pathways, as supported by the verified literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CBS | Cystathionine beta-synthase; catalyzes the first step of transsulfuration | Defects cause homocystinuria; studied in amino acid adequacy |
| CTH | Cystathionine gamma-lyase; catalyzes the second step of transsulfuration | Produces cysteine and alpha-ketobutyrate; relevant to sulfur amino acid metabolism |
| GCLC | Glutamate-cysteine ligase catalytic subunit; first step of glutathione synthesis | Rate-limiting for glutathione; affected by cysteine availability |
| GCLM | Glutamate-cysteine ligase modifier subunit; regulates GCLC activity | Modulates glutathione synthesis under oxidative stress |
| GSS | Glutathione synthetase; second step of glutathione synthesis | Deficiency causes hemolytic anemia; linked to cysteine metabolism |
| ATG4B | Cysteine protease that cleaves ATG8 family proteins | Target for autophagy inhibition; studied with benzotropolones |
| PSMA1 | Proteasome subunit alpha 1; part of ubiquitin-proteasome pathway | Required for lens cell proliferation and differentiation |
| PSMB5 | Proteasome subunit beta 5; catalytic subunit | Involved in proteolysis; relevant to lens pathology |
| UBB | Ubiquitin B; tags proteins for proteasomal degradation | Essential for protein turnover; studied in lens cells |
| UBC | Ubiquitin C; polyubiquitin precursor | Involved in proteolysis and stress responses |
| CASP3 | Caspase 3; cysteine-aspartic protease | Executioner of apoptosis; may be affected by cysteine availability |
| CASP7 | Caspase 7; cysteine protease | Involved in apoptosis; relevant to tissue remodeling |
| CTSB | Cathepsin B; cysteine protease | Lysosomal protease; linked to proteolysis in lens |
| CTSL | Cathepsin L; cysteine protease | Degrades extracellular matrix; studied in fat body destruction |
| NCF1 | Neutrophil cytosolic factor 1; involved in oxidative burst | May be modulated by N-acetyl cysteine |
| NFE2L2 | Nrf2; transcription factor regulating antioxidant response | Controls glutathione synthesis genes; affected by cysteine |
| SLC7A11 | Cystine/glutamate antiporter; imports cystine for cysteine synthesis | Regulates cysteine availability and ferroptosis |
| GOT1 | Glutamic-oxaloacetic transaminase 1; links cysteine catabolism to TCA cycle | Involved in amino acid metabolism |
How Is obsolete cysteine metabolic process Regulated?
Cysteine metabolism is regulated at multiple levels. The transsulfuration pathway is controlled by the availability of methionine and the activity of cystathionine beta-synthase, which is activated by S-adenosylmethionine. Glutathione synthesis is feedback-inhibited by glutathione itself and regulated by Nrf2-mediated transcription of GCLC and GCLM. In pathophysiological states, amino acid adequacy influences the flux through these pathways. Additionally, the ubiquitin-proteasome pathway, which depends on cysteine proteases, is regulated by ubiquitination and deubiquitination. Autophagy, which involves the cysteine protease Atg4B, is regulated by nutrient status and stress.
obsolete cysteine metabolic process and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CBS | Homocystinuria; arsenicosis | Knockout mouse or cell model with CBS mutation |
| CTH | Cysteine deficiency; oxidative stress | CTH knockout cells for transsulfuration studies |
| GCLC | Glutathione deficiency; hemolytic anemia | GCLC knockout cells for glutathione synthesis |
| ATG4B | Autophagy dysregulation; cancer | ATG4B knockout or inhibitor-treated cells |
| PSMA1 | Lens cataract; proteasome dysfunction | PSMA1 knockdown in lens epithelial cells |
Arsenicosis and Sulfur Amino Acid Metabolism
Arsenicosis is a major public health problem caused by chronic arsenic exposure. Arsenic disrupts sulfur amino acid metabolism, including cysteine pathways, leading to oxidative stress and tissue damage. Studies have shown that arsenic affects the transsulfuration pathway and glutathione synthesis, which are dependent on cysteine. Therefore, understanding cysteine metabolism is relevant to developing interventions for arsenicosis.
Lens Pathology and Proteolysis
The lens is a unique tissue where proteolysis and protein quality control are critical for transparency. Ubiquitin-proteasome pathway function is required for lens cell proliferation and differentiation. Cysteine proteases, such as cathepsins and caspases, are involved in lens protein degradation. Dysregulation of these pathways can lead to cataract formation. Thus, cysteine metabolism and cysteine-dependent proteases are important in lens biology.
Aging and T Cell Proteodynamics
Aging is associated with changes in proteodynamics, including altered protein synthesis and degradation in human T cells. These changes may involve cysteine metabolism, as cysteine is required for protein synthesis and redox regulation. Comprehensive study of proteodynamics is needed to understand the fine regulation of T lymphocyte functions during aging.
Autophagy and Cancer
Autophagy is a cellular degradation process that depends on cysteine proteases such as Atg4B. Inhibition of Atg4B by benzotropolones blocks autophagy, suggesting that cysteine protease activity is a target for cancer therapy. Therefore, cysteine metabolism intersects with autophagy regulation and cancer biology.
From obsolete cysteine metabolic process-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of CBS affect cysteine synthesis? | CBS knockout cell line (e.g., HepG2) |
| Does CTH mutation alter glutathione levels? | CTH point-mutation knock-in cells |
| Can cysteine metabolism be monitored in real time? | Tagged knock-in of CBS or CTH with fluorescent reporter |
| Does overexpression of GCLC protect against oxidative stress? | GCLC overexpression cell model |
| Is Atg4B required for autophagy? | ATG4B knockout cells treated with autophagy inducers |
| Does proteasome inhibition affect lens cell differentiation? | PSMA1 knockout or knockdown in lens epithelial cells |
How to Study the obsolete cysteine metabolic process Process
| Method | What It Measures | Typical Application |
|---|---|---|
| HPLC | Amino acid concentrations | Cysteine quantification in plasma or cells |
| Mass spectrometry | Metabolite profiling | Sulfur amino acid metabolism |
| Fluorogenic proteolysis assay | Protease activity | Cysteine protease activity in lens |
| Proteasome activity assay | Chymotrypsin-like activity | Ubiquitin-proteasome function |
| Immunoblotting | Protein levels and ubiquitination | Protein degradation studies |
| GFP-LC3 puncta | Autophagosome formation | Autophagy flux |
| Atg4B enzyme assay | Cysteine protease activity | Autophagy inhibition studies |
| N-acetyl cysteine treatment | Redox modulation | Biomedical applications |
Amino Acid Analysis
Quantification of cysteine and related amino acids in biological samples can be performed using HPLC or mass spectrometry. These methods are essential for assessing amino acid adequacy in pathophysiological states.
Proteolysis Assays
Proteolysis can be measured using fluorogenic substrates or gel-based assays. In lens research, proteolysis assays help evaluate the role of cysteine proteases in protein degradation.
Ubiquitin-Proteasome Pathway Analysis
The ubiquitin-proteasome pathway can be studied using proteasome activity assays, ubiquitin immunoblots, and siRNA knockdown. These methods are used to investigate lens cell proliferation and differentiation.
Autophagy Flux Assays
Autophagy can be monitored using LC3 lipidation assays, GFP-LC3 puncta formation, and autophagy inhibitors. Atg4B activity can be assessed with recombinant enzymes and specific substrates.
How CRISPR Can Be Used to Study GO:0006534 obsolete cysteine metabolic process
Knockout
CRISPR knockout of genes involved in cysteine metabolism, such as CBS or CTH, can be used to study the consequences of loss of function. For example, CBS knockout cells show impaired transsulfuration and altered cysteine levels. These models are valuable for understanding amino acid adequacy in disease.
Point Mutation
Point mutations in cysteine metabolic genes can mimic human disease variants. For instance, introducing a pathogenic mutation in CBS can recapitulate homocystinuria phenotypes in cell models. Such models help dissect the molecular mechanisms of disease.
Knock-in
Knock-in of tagged versions of cysteine metabolic enzymes, such as GFP-tagged CBS, allows real-time imaging and localization studies. This approach can reveal dynamic changes in enzyme localization under stress.
Overexpression
Overexpression of genes like GCLC can enhance glutathione synthesis and protect cells from oxidative stress. Such models are useful for testing antioxidant interventions.
How EDITGENE Supports obsolete cysteine metabolic process Research
Researchers studying obsolete cysteine metabolic process-related genes often need to determine whether a candidate gene is causally involved in cysteine homeostasis, redox regulation, or related diseases. EDITGENE provides comprehensive CRISPR services to generate precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for obsolete cysteine metabolic process research.
Frequently Asked Questions About obsolete cysteine metabolic process
What is GO:0006534?
GO:0006534 is an obsolete Gene Ontology term for cysteine metabolic process, defined as the chemical reactions and pathways involving cysteine.
Why is GO:0006534 obsolete?
It was obsoleted because more specific child terms now cover cysteine biosynthesis, catabolism, and transsulfuration.
What genes are involved in cysteine metabolism?
Key genes include CBS, CTH, GCLC, GCLM, GSS, and SLC7A11, among others.
How is cysteine metabolism studied?
Methods include amino acid analysis, proteolysis assays, ubiquitin-proteasome pathway analysis, and autophagy flux assays.
What diseases are linked to cysteine metabolism?
Arsenicosis, lens pathology, aging T cell dysfunction, and autophagy-related cancers are linked to cysteine metabolism.
What is the role of cysteine in glutathione synthesis?
Cysteine is the rate-limiting substrate for glutathione synthesis, a major antioxidant.
Can CRISPR be used to study cysteine metabolism?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models can be used to study genes involved in cysteine metabolism.
What is the relationship between cysteine and autophagy?
The cysteine protease Atg4B is essential for autophagy, and its inhibition blocks autophagosome formation.
How does arsenic affect cysteine metabolism?
Arsenic disrupts sulfur amino acid metabolism, including cysteine pathways, leading to oxidative stress.
What are the current GO terms for cysteine metabolism?
Current terms include cysteine biosynthetic process (GO:0019344) and cysteine catabolic process (GO:0044273).
Conclusion
GO:0006534 (obsolete cysteine metabolic process) is a historical Gene Ontology term that, despite its obsoletion, remains relevant for interpreting legacy annotations. Cysteine metabolism is fundamental to redox homeostasis, protein synthesis, and disease processes such as arsenicosis and lens pathology. Researchers should map obsolete annotations to current terms and use advanced CRISPR models to dissect the roles of genes like CBS, CTH, and ATG4B. EDITGENE provides the tools and services to accelerate this research.
References
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- 3. Pandey R et al.. 2024. N-Acetyl Cysteine-Decorated Nitric Oxide-Releasing Interface for Biomedical Applications.. ACS Appl Mater Interfaces 16(19):24248-24260 PMID: 38693878
- 4. Witkowski JM et al.. 2018. Proteodynamics in aging human T cells - The need for its comprehensive study to understand the fine regulation of T lymphocyte functions.. Exp Gerontol 107:161-168 PMID: 29038026
- 5. David LL et al.. 1989. Role of proteolysis in lenses: a review.. Lens Eye Toxic Res 6(4):725-47 PMID: 2562121
- 6. Guo SY et al.. 2018. 20-Hydroxyecdysone-upregulated proteases involved in Bombyx larval fat body destruction.. Insect Mol Biol 27(6):724-738 PMID: 29888823
- 7. Tanc M et al.. 2019. Synthesis and evaluation of novel benzotropolones as Atg4B inhibiting autophagy blockers.. Bioorg Chem 87:163-168 PMID: 30884310
- 8. Guo W et al.. 2006. Ubiquitin-proteasome pathway function is required for lens cell proliferation and differentiation.. Invest Ophthalmol Vis Sci 47(6):2569-75 PMID: 16723472
