GO:0003839 gamma-glutamylcyclotransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0003839 (gamma-glutamylcyclotransferase activity) catalyzes the conversion of (5-L-glutamyl)-L-amino acids to 5-oxoproline and free L-amino acids, a key step in glutathione turnover and amino acid recycling.
• The enzyme is a novel cancer target: its expression is elevated in multiple malignancies and its inhibition or depletion suppresses proliferation and induces senescence.
• GGCT (gamma-glutamylcyclotransferase) is transcriptionally regulated by c-Jun and controls glioblastoma stem cell proliferation through Notch1 levels.
• In breast cancer cells, GGCT depletion induces p15(INK4b) and p21(Cip1)-mediated senescence via TGF-β2/SMAD3 pathway activation.
• GGCT activity can be monitored with activity-based chemiluminogenic probes, enabling high-throughput screening and functional studies.
• Plant and mammalian studies link gamma-glutamylcyclotransferase to glutathione homeostasis, sulfur starvation responses, and ferroptosis regulation.
Description
Gamma-glutamylcyclotransferase activity (GO:0003839) is a molecular function that removes the gamma-glutamyl group from (5-L-glutamyl)-L-amino acids, producing 5-oxoproline (pyroglutamate) and a free amino acid. This reaction is central to the gamma-glutamyl cycle, which governs glutathione homeostasis, amino acid transport, and cellular redox balance. Because glutathione metabolism is frequently rewired in cancer and other diseases, this enzymatic activity has emerged as a promising diagnostic and therapeutic target. Researchers study GO:0003839 to understand how cells recycle glutathione, respond to oxidative stress, and regulate proliferation and senescence. The enzyme has been characterized biochemically and structurally, and its activity can be measured with chemiluminogenic probes, making it accessible to both basic and translational research. This article synthesizes the current knowledge of GO:0003839, its genes, regulation, disease links, and experimental models.
gamma-glutamylcyclotransferase activity At A Glance
| GO ID | GO:0003839 |
|---|---|
| GO term | gamma-glutamylcyclotransferase activity |
| Ontology | molecular_function |
| Synonym | (5-L-glutamyl)-L-amino-acid 5-glutamyltransferase (cyclizing); gamma-glutamyl-amino acid cyclotransferase activity; gamma-L-glutamylcyclotransferase activity; L-glutamic cyclase activity |
| Definition | Catalysis of the reaction: (5-L-glutamyl)-L-amino acid = 5-oxoproline + L-amino acid. |
| Major function | Removes gamma-glutamyl groups from gamma-glutamyl-amino acids, generating 5-oxoproline and free amino acids; key in glutathione turnover and amino acid recycling. |
| Substrates | (5-L-glutamyl)-L-amino acids, including gamma-glutamyl-cysteine and gamma-glutamyl peptides. |
| Products | 5-oxoproline (pyroglutamate) and L-amino acids. |
| Related genes | GGCT (gamma-glutamylcyclotransferase), CHAC1/2 (glutathione-specific gamma-glutamylcyclotransferases). |
| Disease relevance | Cancer (breast, glioblastoma, others), ferroptosis, oxidative stress. |
What Is GO:0003839?
GO:0003839, gamma-glutamylcyclotransferase activity, is defined by the Gene Ontology as the catalysis of the reaction: (5-L-glutamyl)-L-amino acid = 5-oxoproline + L-amino acid. In other words, the enzyme cleaves the gamma-glutamyl bond of a gamma-glutamyl-amino acid, releasing the amino acid and forming 5-oxoproline (also called pyroglutamate). This activity is synonymous with (5-L-glutamyl)-L-amino-acid 5-glutamyltransferase (cyclizing), gamma-glutamyl-amino acid cyclotransferase, gamma-L-glutamylcyclotransferase, and L-glutamic cyclase. It is a molecular function that contributes to glutathione catabolism and amino acid recycling.
Why Is gamma-glutamylcyclotransferase activity Important in Cell Biology?
GO:0003839 is important because it controls the flux of glutathione and amino acids through the gamma-glutamyl cycle, influencing cellular redox status, proliferation, and survival. Dysregulation of this activity is linked to cancer progression, where elevated GGCT supports tumor growth and stemness. In breast cancer, GGCT depletion triggers senescence via TGF-β2/SMAD3 signaling, highlighting its role in cell-cycle control. In glioblastoma stem cells, GGCT is regulated by c-Jun and affects Notch1 levels, connecting it to developmental signaling. Moreover, gamma-glutamylcyclotransferase activity is implicated in ferroptosis and radiosensitivity through glutathione detoxification pathways. Thus, understanding GO:0003839 offers opportunities for biomarker development and targeted therapy.
• Drives glutathione turnover and amino acid recycling, maintaining redox homeostasis.
• Elevated in multiple cancers and associated with poor prognosis, making it a candidate therapeutic target.
• Regulates proliferation and senescence in breast cancer cells via TGF-β2/SMAD3.
• Controls glioblastoma stem cell proliferation through Notch1 and is transcriptionally regulated by c-Jun.
• Modulates ferroptosis and radiosensitivity by affecting glutathione detoxification.
• In plants, affects glutathione content and root architecture during sulfur starvation.
• Can be measured with activity-based chemiluminogenic probes for drug discovery.
• Links to oxidative stress responses and neurotrophic factor signaling.
Molecular Mechanism of gamma-glutamylcyclotransferase activity
Substrate recognition and binding
In simple terms: The enzyme grabs a gamma-glutamyl-amino acid and positions it for cleavage.
Gamma-glutamylcyclotransferase (GGCT) recognizes (5-L-glutamyl)-L-amino acids, such as gamma-glutamyl-cysteine, through a conserved active site that accommodates the gamma-glutamyl moiety and the amino acid side chain. Substrate specificity studies indicate preference for certain gamma-glutamyl peptides, and the enzyme does not act on free glutathione directly but on its degradation products.
Catalytic cyclization and product release
In simple terms: The enzyme cuts the bond and the gamma-glutamyl part curls into a ring, releasing the amino acid.
The catalytic mechanism involves nucleophilic attack and cyclization, converting the gamma-glutamyl group into 5-oxoproline (pyroglutamate) while releasing the free amino acid. This reaction is part of the gamma-glutamyl cycle, which facilitates amino acid transport and glutathione synthesis.
Cofactors and metal requirements
In simple terms: The enzyme does not need metal helpers; it uses its own amino acids to do the chemistry.
Gamma-glutamylcyclotransferase activity is metal-independent and does not require ATP or other cofactors; the reaction proceeds via a general acid-base mechanism involving active-site residues. This simplicity makes it amenable to activity-based probe development.
Regulation by signaling pathways
In simple terms: Other signals tell the cell to make more or less of this enzyme.
GGCT expression is transcriptionally regulated by c-Jun in glioblastoma stem cells, and its activity can be influenced by glutathione levels and oxidative stress. In breast cancer, GGCT depletion activates TGF-β2/SMAD3 signaling, leading to senescence. Additionally, neurotrophic factors such as MANF can suppress ferroptosis via PERK/ATF4, indirectly affecting glutathione metabolism.
Role in glutathione homeostasis and ferroptosis
In simple terms: This enzyme helps recycle glutathione, and when it is off, cells can die from iron-dependent damage.
By breaking down gamma-glutamyl peptides, GGCT contributes to glutathione turnover and cysteine availability. In liver cancer, PEX5 deficiency enhances radiosensitivity via MGST1-GSH detoxifying function and promotes ferroptosis, linking glutathione metabolism to cell death. Thus, GO:0003839 activity is integrated into redox and ferroptosis networks.
Key Genes Involved in GO:0003839 gamma-glutamylcyclotransferase activity
The following genes and proteins are directly or indirectly associated with gamma-glutamylcyclotransferase activity (GO:0003839) and its biological roles.
| Gene | Major Role | Research Relevance |
|---|---|---|
| GGCT | Encodes gamma-glutamylcyclotransferase, the enzyme that catalyzes GO:0003839 | Cancer target; regulates proliferation and senescence |
| CHAC1 | Glutathione-specific gamma-glutamylcyclotransferase 1; degrades glutathione | Upregulated by 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole; involved in oxidative stress |
| CHAC2 | Glutathione-specific gamma-glutamylcyclotransferase 2 | Paralog of CHAC1; potential role in glutathione homeostasis |
| JUN | Transcription factor c-Jun; regulates GGCT expression | Controls glioblastoma stem cell proliferation via GGCT/Notch1 |
| NOTCH1 | Notch receptor; downstream of GGCT in glioblastoma stem cells | Modulated by GGCT levels; affects stemness |
| SMAD3 | TGF-β signaling effector; activated upon GGCT depletion | Mediates senescence in breast cancer cells |
| CDKN2B | p15(INK4b); cyclin-dependent kinase inhibitor | Induced by GGCT depletion; triggers senescence |
| CDKN1A | p21(Cip1); cyclin-dependent kinase inhibitor | Induced by GGCT depletion; triggers senescence |
| TGFB2 | TGF-β2; cytokine upregulated upon GGCT depletion | Activates SMAD3 to induce senescence |
| MGST1 | Microsomal glutathione S-transferase 1; detoxifies lipid peroxides | Linked to GSH detoxification and ferroptosis in liver cancer |
| PEX5 | Peroxisomal biogenesis factor; affects MGST1-GSH function | Deficiency enhances radiosensitivity and ferroptosis |
| MANF | Mesencephalic astrocyte-derived neurotrophic factor; suppresses ferroptosis | Acts via PERK/ATF4; affects depressive-like behaviors |
| ATF4 | Activating transcription factor 4; ISR effector | Mediates MANF effects on ferroptosis |
| PERK | ER stress kinase; upstream of ATF4 | Part of MANF signaling to suppress ferroptosis |
| GGCT (plant homolog) | Arabidopsis gamma-glutamylcyclotransferase | Affects glutathione content and root architecture during sulfur starvation |
How Is gamma-glutamylcyclotransferase activity Regulated?
Gamma-glutamylcyclotransferase activity is regulated at multiple levels. Transcriptionally, GGCT is a target of c-Jun, which controls its expression in glioblastoma stem cells and influences Notch1 levels. In breast cancer, GGCT depletion activates TGF-β2/SMAD3 signaling, suggesting feedback regulation between GGCT and TGF-β pathways. Glutathione-specific gamma-glutamylcyclotransferase 1 (CHAC1) is upregulated by 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole, indicating small-molecule regulation. Additionally, neurotrophic factor MANF suppresses ferroptosis via PERK/ATF4, which may indirectly affect glutathione metabolism and GGCT activity. In plants, sulfur starvation alters gamma-glutamylcyclotransferase expression and glutathione content.
gamma-glutamylcyclotransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| GGCT | Breast cancer; senescence | MCF-7 or MDA-MB-231 knockout and overexpression |
| GGCT | Glioblastoma; stem cell proliferation | Patient-derived glioblastoma stem cell knockout |
| CHAC1 | Oxidative stress; glutathione depletion | HEK293 or cancer cell lines with CHAC1 knockout |
| MGST1/PEX5 | Liver cancer; ferroptosis and radiosensitivity | HepG2 or Huh7 knockout models |
| MANF/ATF4 | Depression; ferroptosis | Neuronal cell lines or mouse models |
Cancer
GGCT is overexpressed in various cancers and is considered a novel target for diagnosis and treatment. In breast cancer cells, GGCT depletion induces p15(INK4b) and p21(Cip1)-mediated senescence via TGF-β2/SMAD3 pathway activation, suggesting that inhibiting GGCT could suppress tumor growth. In glioblastoma stem cells, GGCT is transcriptionally regulated by c-Jun and controls proliferation through Notch1 levels, highlighting its role in brain tumor stemness. These findings support GGCT as a therapeutic target in oncology.
Ferroptosis and oxidative stress
Gamma-glutamylcyclotransferase activity contributes to glutathione homeostasis, and its dysregulation can influence ferroptosis, an iron-dependent form of cell death. In liver cancer, PEX5 deficiency enhances radiosensitivity via MGST1-GSH detoxifying function and promotes ferroptosis, linking glutathione metabolism to cell death. MANF suppresses ferroptosis via PERK/ATF4 signaling, further connecting glutathione-related pathways to cell survival.
Metabolic and plant stress responses
In Arabidopsis, gamma-glutamylcyclotransferase affects glutathione content and root system architecture during sulfur starvation, demonstrating a conserved role in sulfur and glutathione metabolism. This suggests that GO:0003839 is important for adaptive responses to nutrient stress.
From gamma-glutamylcyclotransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does GGCT loss affect cancer cell proliferation? | CRISPR knockout of GGCT in breast or glioblastoma cell lines |
| Does a point mutation in the active site abolish enzymatic activity? | CRISPR point mutation (e.g., catalytic residue) followed by activity assay |
| Does GGCT overexpression drive transformation? | Knock-in of a constitutive promoter or overexpression vector |
| How does GGCT depletion alter signaling pathways? | Knockout combined with RNA-seq and phosphoproteomics |
| Can GGCT activity be monitored in live cells? | Activity-based chemiluminogenic probe with knockout controls |
| What is the role of GGCT in ferroptosis? | Knockout in liver cancer cells treated with ferroptosis inducers |
How to Study the gamma-glutamylcyclotransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Chemiluminogenic probe assay | Gamma-glutamylcyclotransferase enzymatic activity | High-throughput screening and kinetic studies |
| CRISPR knockout screening | Gene essentiality and synthetic lethality | Identifying modifiers of GGCT inhibitor sensitivity |
| RNA-seq | Transcriptional changes | Pathway analysis after GGCT depletion |
| Proteomics | Protein expression and modifications | Signaling changes in knockout models |
| Metabolomics | Glutathione and amino acid levels | Redox and ferroptosis studies |
| Western blot | Protein levels of GGCT and effectors | Validation of knockout or overexpression |
| Immunohistochemistry | Tissue expression of GGCT | Cancer biomarker studies |
| Flow cytometry | Cell cycle and senescence | Senescence induction after GGCT depletion |
Enzymatic activity assays
Gamma-glutamylcyclotransferase activity can be measured using activity-based chemiluminogenic probes that detect the release of 5-oxoproline or the consumption of gamma-glutamyl substrates. These assays are suitable for high-throughput screening and kinetic characterization.
CRISPR-based genetic screens
Genome-wide CRISPR knockout screens can identify genes that modulate sensitivity to GGCT inhibition or glutathione depletion. Such screens help uncover synthetic lethal interactions and resistance mechanisms.
Transcriptomics and proteomics
RNA-seq and proteomics can reveal changes in gene expression and signaling pathways upon GGCT knockout or overexpression, as shown in breast cancer and glioblastoma studies. These methods identify downstream effectors such as TGF-β2, SMAD3, and Notch1.
Metabolomics and glutathione quantification
Metabolomic profiling and glutathione assays can measure the impact of GGCT modulation on cellular redox state and amino acid pools. This is particularly relevant for studying ferroptosis and oxidative stress.
How CRISPR Can Be Used to Study GO:0003839 gamma-glutamylcyclotransferase activity
Knockout
CRISPR knockout of GGCT or CHAC1 is used to abolish gamma-glutamylcyclotransferase activity and study its consequences on proliferation, senescence, and glutathione metabolism. Knockout cell lines serve as negative controls for activity assays and as models for drug sensitivity.
Point Mutation
CRISPR point mutation can be used to mutate catalytic residues of GGCT, allowing researchers to distinguish enzymatic activity from scaffolding functions. Such mutants are valuable for validating activity-based probes and for structure-function studies.
Knock-in
Knock-in of tagged GGCT (e.g., FLAG or GFP) enables localization, interaction, and degradation studies. Knock-in of disease-associated variants or promoter reporters can reveal transcriptional regulation by c-Jun or other factors.
Overexpression
Overexpression of GGCT or CHAC1 via CRISPR activation or lentiviral vectors can model the elevated enzyme levels seen in cancers. Overexpression models help test whether increased activity drives proliferation or resistance to ferroptosis.
How EDITGENE Supports gamma-glutamylcyclotransferase activity Research
Researchers studying gamma-glutamylcyclotransferase activity-related genes often need to determine whether a candidate gene is causally involved in glutathione metabolism, cancer progression, or ferroptosis. EDITGENE provides comprehensive CRISPR services to generate precisely engineered cell models for such functional studies.
Contact EDITGENE today to design your custom CRISPR model for gamma-glutamylcyclotransferase activity research.
Frequently Asked Questions About gamma-glutamylcyclotransferase activity
What is gamma-glutamylcyclotransferase activity?
It is the enzymatic activity defined by GO:0003839 that converts (5-L-glutamyl)-L-amino acids to 5-oxoproline and free L-amino acids, playing a key role in glutathione turnover.
What genes are involved in gamma-glutamylcyclotransferase activity?
The main gene is GGCT, which encodes the enzyme. Related genes include CHAC1 and CHAC2, which encode glutathione-specific gamma-glutamylcyclotransferases.
What is the function of GGCT in cancer?
GGCT is overexpressed in several cancers and supports proliferation and stemness; its depletion induces senescence or reduces tumor growth.
How is gamma-glutamylcyclotransferase activity measured?
It can be measured using activity-based chemiluminogenic probes that detect the enzymatic reaction products.
What diseases are associated with gamma-glutamylcyclotransferase activity?
It is linked to breast cancer, glioblastoma, liver cancer, ferroptosis, and oxidative stress-related conditions.
What is the role of GGCT in glioblastoma?
GGCT is transcriptionally regulated by c-Jun and controls glioblastoma stem cell proliferation through Notch1 levels.
How does GGCT depletion affect breast cancer cells?
It induces p15(INK4b) and p21(Cip1)-mediated senescence via TGF-β2/SMAD3 pathway activation.
Is gamma-glutamylcyclotransferase activity involved in ferroptosis?
Yes, it contributes to glutathione homeostasis, and its dysregulation can influence ferroptosis and radiosensitivity.
What are the synonyms for GO:0003839?
Synonyms include (5-L-glutamyl)-L-amino-acid 5-glutamyltransferase (cyclizing), gamma-glutamyl-amino acid cyclotransferase activity, gamma-L-glutamylcyclotransferase activity, and L-glutamic cyclase activity.
How can CRISPR help study gamma-glutamylcyclotransferase activity?
CRISPR knockout, point mutation, knock-in, and overexpression models allow researchers to dissect the causal roles of GGCT and related genes in cells and disease models.
Conclusion
Gamma-glutamylcyclotransferase activity (GO:0003839) is a fundamental enzymatic function in glutathione metabolism and amino acid recycling, with emerging roles in cancer, ferroptosis, and stress responses. The enzyme GGCT and its paralogs CHAC1/2 are regulated by signaling pathways such as c-Jun and TGF-β, and their dysregulation contributes to tumor progression and senescence. Advances in activity-based probes and CRISPR models are accelerating research into this target. Understanding GO:0003839 offers new opportunities for therapeutic intervention and biomarker development.
References
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