CHAC1 (glutathione-specific gamma-glutamylcyclotransferase 1; EC 4.3.2.7) is a cytosolic enzyme of the ChaC subfamily of gamma-glutamylcyclotransferases that carries out the committed step of a dedicated intracellular glutathione degradation route, distinct from the extracellular gamma-glutamyl transferase (GGT1) pathway. It cleaves the gamma-glutamyl bond of reduced glutathione (GSH) to yield 5-oxo-L-proline (pyroglutamate) and the dipeptide L-cysteinylglycine, acting specifically on GSH and not on other gamma-glutamyl peptides or oxidized glutathione. CHAC1 expression is tightly controlled and is strongly induced as a downstream target of the ATF4-ATF3-CHOP arm of the integrated stress response and unfolded protein response under endoplasmic reticulum stress. By depleting intracellular GSH, CHAC1 acts as a pro-apoptotic effector and sensitizes cells to oxidative-stress-driven death, including ferroptosis. The protein (historically called Botch, Blocks Notch) has an additional reported role as a negative regulator of Notch signaling during embryonic neurogenesis, in which it binds the Notch extracellular region and blocks the furin-mediated S1 maturation cleavage of Notch, keeping the receptor in an immature inactive form; this activity has been characterized chiefly in the rodent ortholog and involves a trans-Golgi pool of the protein.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0006751 glutathione catabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) transfer of the family-defining process. CHAC1 performs the committed intracellular step of glutathione degradation, cleaving GSH to 5-oxoproline and cysteinylglycine. Well supported by experimental catalytic data and by UniProt; this is a core biological process for the gene. Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt Reaction=glutathione = L-cysteinylglycine + 5-oxo-L-proline |
| GO:0061928 glutathione specific gamma-glutamylcyclotransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) transfer of the core molecular function. This is the defining enzymatic activity of CHAC1, independently confirmed experimentally (EC 4.3.2.7; RHEA:47724). Core molecular function. Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt Acts specifically on glutathione, but not on |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | MODIFY | Summary: IBA cytoplasm annotation. Correct but non-specific; the experimentally supported location is the cytosol (GO:0005829, IDA in this dataset). Retained as a true but general localization. Reason: cytoplasm is a broad parent; the more precise, experimentally supported term cytosol (GO:0005829) is available and is used as the core location. Proposed replacements: cytosol Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm, cytosol |
| GO:0005794 Golgi apparatus | IEA GO_REF:0000044 | MARK AS OVER ANNOTATED | Summary: IEA from UniProt Subcellular Location vocabulary mapping. The Golgi annotation derives from a trans-Golgi-network pool inferred by similarity to the mouse ortholog (Botch), relevant only to the secondary Notch-regulatory role. The bare parent Golgi apparatus is over-broad relative to the trans-Golgi network term and is not the core location for the enzyme (whose experimental location is the cytosol). Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt Golgi apparatus, trans-Golgi network |
| GO:0005829 cytosol | IEA GO_REF:0000044 | ACCEPT | Summary: IEA cytosol from Subcellular Location mapping, consistent with the experimental IDA (PMID:19109178). Correct core location. Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm, cytosol |
| GO:0006751 glutathione catabolic process | IEA GO_REF:0000120 | ACCEPT | Summary: IEA (InterPro/ortholog-based) transfer of the core glutathione catabolic process. Correct and consistent with experimental catalytic data. Core BP. Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt Reaction=glutathione = L-cysteinylglycine + 5-oxo-L-proline |
| GO:0061928 glutathione specific gamma-glutamylcyclotransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: IEA transfer of the core molecular function (via InterPro IPR006840, RHEA:47724, EC:4.3.2.7). Correct core MF, redundant with the experimental IDA and EXP annotations. Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt EC=4.3.2.7 |
| GO:0005515 protein binding | IPI PMID:16189514 Towards a proteome-scale map of the human protein-protein in... | MARK AS OVER ANNOTATED | Summary: Bare protein binding from a high-throughput yeast two-hybrid interactome screen (Rual et al.); the recorded partner is RHOXF2 (Q9BQY4). This uninformative term conveys no specific function and does not represent a characterized interaction relevant to CHAC1 biology. Retained (experimental IPI is not removed) but flagged as over-annotation. Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt Q9BUX1; Q9BQY4: RHOXF2; NbExp=2 |
| GO:0005112 Notch binding | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: IEA transfer (Ensembl Compara) from the mouse ortholog Botch (Q8R3J5), which binds the Notch1 extracellular region. This reflects the secondary, moonlighting Notch-regulatory role rather than the core enzymatic function. Retained as non-core; the interaction is genuine but characterized chiefly in rodent and is not CHAC1's core evolved activity. Supporting Evidence: PMID:22445366 Botch interacts with the extracellular domain of Notch1 (NECD1) |
| GO:0005802 trans-Golgi network | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: IEA transfer from the mouse ortholog of a trans-Golgi-network pool where Botch blocks furin S1 cleavage of Notch. Relevant only to the secondary Notch role; not the core (cytosolic) enzymatic location. Kept as non-core. Supporting Evidence: PMID:22445366 indicating that in the Golgi, Botch resides in the trans-Golgi |
| GO:0022008 neurogenesis | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: IEA transfer from the mouse ortholog of the developmental neurogenesis role (Botch promotes neuronal differentiation by antagonizing Notch). Genuine but a pleiotropic/secondary developmental process, not the core metabolic function. Kept as non-core. Supporting Evidence: PMID:22445366 Botch regulates neurogenesis by promoting |
| GO:0006749 glutathione metabolic process | TAS Reactome:R-HSA-174403 | MODIFY | Summary: Reactome TAS placing CHAC1 in glutathione metabolism. Correct but a broad parent of the more specific catabolic process (GO:0006751) that CHAC1 actually performs. Retained as a true, if general, process annotation. Reason: glutathione metabolic process is the broad parent; CHAC1 specifically catabolizes GSH, so the catabolic child term is more informative. Proposed replacements: glutathione catabolic process |
| GO:0061928 glutathione specific gamma-glutamylcyclotransferase activity | EXP PMID:27913623 ChaC2, an Enzyme for Slow Turnover of Cytosolic Glutathione. | ACCEPT | Summary: Experimental (EXP) assignment of the core catalytic activity. Kaur et al. purified and kinetically characterized human ChaC1, reporting Km 2.2 mM and kcat 225.2 per min for glutathione, with specificity for reduced GSH only. Directly supports the core molecular function. Supporting Evidence: PMID:27913623 kcat of 225.2 ± 15 min-1 toward glutathione for human ChaC1 |
| GO:0005829 cytosol | TAS Reactome:R-HSA-6785928 | ACCEPT | Summary: Reactome TAS cytosol annotation for the CHAC1/2 GSH-cleavage reaction. Consistent with the experimental IDA; correct core location. Supporting Evidence: file:human/CHAC1/CHAC1-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm, cytosol |
| GO:0061928 glutathione specific gamma-glutamylcyclotransferase activity | IDA PMID:27913623 ChaC2, an Enzyme for Slow Turnover of Cytosolic Glutathione. | ACCEPT | Summary: Direct assay (IDA) of the core catalytic activity from the same study that characterized human ChaC1 kinetics and its strict specificity for reduced glutathione (no activity on gamma-glutamyl amino acids or oxidized GSH). Strong experimental support for the core molecular function. Supporting Evidence: PMID:27913623 no activity against either |
| GO:0005112 Notch binding | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS annotation of Notch binding by sequence-similarity transfer from mouse Botch (Q8R3J5). Same secondary Notch-regulatory function as the IEA Notch binding annotation above; kept as non-core. Supporting Evidence: PMID:22445366 Botch interacts with the extracellular domain of Notch1 (NECD1) |
| GO:0005802 trans-Golgi network | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS trans-Golgi-network location transferred from mouse Botch, tied to the Notch-processing role. Not the core cytosolic enzymatic location; kept as non-core. Supporting Evidence: PMID:22445366 indicating that in the Golgi, Botch resides in the trans-Golgi |
| GO:0010955 negative regulation of protein processing | IMP PMID:22445366 Botch promotes neurogenesis by antagonizing Notch. | KEEP AS NON CORE | Summary: IMP (experimental) annotation from the Botch study: Botch blocks the furin-mediated S1 processing cleavage of Notch, keeping it in the immature full-length form. This captures the mechanism of the secondary Notch role. Experimental annotation retained; marked non-core because it reflects a moonlighting regulatory function (characterized chiefly in rodent), not the core GSH-degrading enzyme activity. Supporting Evidence: PMID:22445366 Botch blocks furin cleavage in a manner similar to the furin inhibitor, DEC-RVKR-CMK |
| GO:0022008 neurogenesis | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS neurogenesis annotation transferred from mouse Botch. Same developmental process as the IEA neurogenesis annotation; a secondary, pleiotropic role. Kept as non-core. Supporting Evidence: PMID:22445366 Botch regulates neurogenesis by promoting |
| GO:0045746 negative regulation of Notch signaling pathway | IMP PMID:22445366 Botch promotes neurogenesis by antagonizing Notch. | KEEP AS NON CORE | Summary: IMP (experimental) annotation: knockdown/overexpression of Botch modulates Notch signaling; Botch inhibits Notch by preventing its furin S1 maturation, antagonizing the pathway during neurogenesis. Experimental annotation retained; the Notch-regulatory role is a genuine secondary function of CHAC1 but is not its core evolved metabolic activity, so kept as non-core. Supporting Evidence: PMID:22445366 inhibiting the S1 furin-like cleavage of Notch |
| GO:0005829 cytosol | IDA PMID:19109178 CHAC1/MGC4504 is a novel proapoptotic component of the unfol... | ACCEPT | Summary: Direct experimental (IDA) evidence that human CHAC1 localizes to the cytosol: CHAC1-V5eGFP fractionated to the cytosolic compartment and showed diffuse cytoplasmic staining, unchanged by UPR induction. This is the core, primary subcellular location of the enzyme. Supporting Evidence: PMID:19109178 CHAC1 was primarily localized in the cytosolic compartment compared with the nucleus or pellet fractions |
| GO:0070059 intrinsic apoptotic signaling pathway in response to endoplasmic reticulum stress | IMP PMID:19109178 CHAC1/MGC4504 is a novel proapoptotic component of the unfol... | KEEP AS NON CORE | Summary: IMP (experimental): CHAC1 is a downstream pro-apoptotic effector of the ATF4-ATF3-CHOP arm of the UPR; its overexpression is sufficient and its knockdown reduces ER-stress-associated apoptosis markers (TUNEL, cleaved PARP, AIF nuclear translocation). This is a genuine and physiologically important role of CHAC1 downstream of ER stress. Retained as non-core because the core evolved function is the enzymatic GSH catabolism that mechanistically drives this pro-apoptotic outcome via GSH depletion. Supporting Evidence: PMID:19109178 CHAC1 expression as necessary and sufficient to induce well-characterized markers of apoptosis, TUNEL, cPARP, and AIF nuclear translocation |
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