Copper chaperone for superoxide dismutase 1 (SOD1). Ccs delivers copper to SOD1 and is essential for SOD1 activation, protein stability, and proper disulfide bond formation. CCS-null mutants phenocopy SOD1 deficiency with reduced lifespan, hypersensitivity to oxidative stress, and loss of cytosolic aconitase activity. Uniquely among characterized CCS proteins, Drosophila Ccs lacks the N-terminal MXCXXC copper-binding motif but retains the C-terminal CXC motif essential for copper transfer. Despite some annotations, Ccs is NOT itself a superoxide dismutase enzyme - those IEA annotations derive from misannotation of the UniProt record.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0019430 removal of superoxide radicals | IEA GO_REF:0000108 | REMOVE | Summary: INCORRECT. This annotation derives from the erroneous UniProt classification of Ccs as a superoxide dismutase (EC 1.15.1.1). Ccs is NOT an SOD enzyme - it is the copper chaperone for SOD1 that delivers copper and promotes SOD1 stability. The actual superoxide dismutase enzyme in the pathway is SOD1/dSod1 [PMID:18948262 "CCS-null mutants phenotypically resemble SOD1-null mutants"]. Falcon deep research confirms Ccs acts upstream as a maturation factor, not the catalytic enzyme. Supporting Evidence: file:DROME/Ccs/Ccs-deep-research-falcon.md CCS has a specialized **post-translational maturation role** rather than acting as the SOD catalytic enzyme itself: it **delivers copper to apo-SOD1** and promotes formation of the mature active enzyme. |
| GO:0098869 cellular oxidant detoxification | IEA GO_REF:0000108 | MARK AS OVER ANNOTATED | Summary: This is an over-annotation. While Ccs indirectly contributes to oxidant detoxification by activating SOD1, the direct cellular oxidant detoxification activity belongs to SOD1 itself. Ccs functions as a copper chaperone upstream of this process [PMID:18948262]. Falcon deep research places Ccs in the copper-handling branch that matures SOD1, with detoxification performed by the resulting active SOD1. Supporting Evidence: file:DROME/Ccs/Ccs-deep-research-falcon.md The primary function of Drosophila Ccs is **post-translational activation and stabilization of cytosolic Cu,Zn-SOD1 (dSOD1)**, via copper delivery and associated maturation chemistry; in CCS-null flies, SOD1 activity becomes essentially undetectable and dSOD1 protein is strongly reduced |
| GO:0004784 superoxide dismutase activity | IEA GO_REF:0000116 | REMOVE | Summary: INCORRECT. This annotation derives from Rhea mapping based on UniProt's erroneous EC 1.15.1.1 assignment. Ccs does NOT have superoxide dismutase activity - it is the copper chaperone for SOD1. The dismutation of superoxide is catalyzed by SOD1, not Ccs [PMID:18948262 "Copper is inserted into the SOD1 apoprotein by a specific chaperone, the copper chaperone for SOD1 (CCS)"]. Falcon deep research independently confirms Ccs is a metallochaperone, not the SOD enzyme. Supporting Evidence: file:DROME/Ccs/Ccs-deep-research-falcon.md CCS has a specialized **post-translational maturation role** rather than acting as the SOD catalytic enzyme itself: it **delivers copper to apo-SOD1** and promotes formation of the mature active enzyme. |
| GO:0005507 copper ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: Accept. As a copper chaperone, Ccs must bind copper to transfer it to SOD1. Drosophila Ccs uniquely lacks the N-terminal MXCXXC copper-binding motif but retains the C-terminal CXC domain III motif that is essential for copper transfer [PMID:18948262 "domain III contains a critical CXC copper-binding site that inserts copper"]. Falcon deep research confirms this Drosophila-specific loss of the canonical domain I motif while retaining copper-delivery function. Supporting Evidence: file:DROME/Ccs/Ccs-deep-research-falcon.md A Drosophila-specific feature highlighted experimentally is that **Drosophila CCS lacks the canonical domain I MXCXXC copper-binding motif**, yet remains capable of supporting SOD1 activation |
| GO:0006801 superoxide metabolic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Over-annotation. Ccs does not directly metabolize superoxide. It functions upstream as a copper chaperone that activates SOD1. SOD1 is the enzyme that directly metabolizes superoxide. The term "superoxide metabolic process" belongs on SOD1, not Ccs [PMID:18948262]. Falcon deep research confirms the primary role is SOD1 maturation, not direct superoxide metabolism. Supporting Evidence: file:DROME/Ccs/Ccs-deep-research-falcon.md CCS has a specialized **post-translational maturation role** rather than acting as the SOD catalytic enzyme itself: it **delivers copper to apo-SOD1** and promotes formation of the mature active enzyme. |
| GO:0016209 antioxidant activity | IEA GO_REF:0000043 | REMOVE | Summary: INCORRECT. This annotation derives from UniProt keyword mapping. Ccs does not have antioxidant activity - it is a copper chaperone. The antioxidant activity (superoxide dismutation) is performed by SOD1, which Ccs activates. Ccs itself does not directly scavenge reactive oxygen species [PMID:18948262]. Falcon deep research confirms Ccs is a metallochaperone upstream of SOD1, not an antioxidant. Supporting Evidence: file:DROME/Ccs/Ccs-deep-research-falcon.md CCS has a specialized **post-translational maturation role** rather than acting as the SOD catalytic enzyme itself: it **delivers copper to apo-SOD1** and promotes formation of the mature active enzyme. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000043 | REMOVE | Summary: INCORRECT. This annotation derives from UniProt keyword mapping. Ccs is not an oxidoreductase - it does not catalyze redox reactions. While CCS does have disulfide isomerase-like activity that oxidizes the intramolecular disulfide in SOD1, this is not oxidoreductase activity in the classic sense. The SOD oxidoreductase activity belongs to SOD1, not Ccs [PMID:18948262]. Falcon deep research describes the maturation as copper insertion plus a disulfide-chemistry step (transient CCS-SOD1 disulfide exchange), not a standalone oxidoreductase catalytic role. Supporting Evidence: file:DROME/Ccs/Ccs-deep-research-falcon.md CCS is **catalytic** relative to SOD1, being at least **~10× less abundant** (molar) while efficiently maturing SOD1 |
| GO:0046872 metal ion binding | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Accept but the more specific term GO:0005507 (copper ion binding) is already included. This general term is redundant given the more specific annotation. Ccs binds copper via its domain III CXC motif [PMID:18948262]. |
| GO:0005737 cytoplasm | IDA PMID:22758915 An inventory of peroxisomal proteins and pathways in Drosoph... | ACCEPT | Summary: Accept. Localization to cytoplasm is consistent with Ccs function as chaperone for cytosolic SOD1. The peroxisome proteomics study confirmed cytoplasmic localization [PMID:22758915]. Supporting Evidence: PMID:22758915 2012 Jul 25. An inventory of peroxisomal proteins and pathways in Drosophila melanogaster. file:DROME/Ccs/Ccs-deep-research-falcon.md Broader CCS-family reviews indicate CCS proteins are mainly **cytosolic**, with additional localization to the **mitochondrial intermembrane space (IMS)** in other systems |
| GO:0005777 peroxisome | IDA PMID:22758915 An inventory of peroxisomal proteins and pathways in Drosoph... | KEEP AS NON CORE | Summary: Accept as non-core localization. Proteomics study identified Ccs in peroxisomes. This is interesting as it suggests Ccs may also function to activate peroxisomal SOD1, though the primary function is in the cytoplasm [PMID:22758915 "An inventory of peroxisomal proteins"]. Supporting Evidence: PMID:22758915 2012 Jul 25. An inventory of peroxisomal proteins and pathways in Drosophila melanogaster. |
| GO:0006979 response to oxidative stress | IMP PMID:18948262 Instability of superoxide dismutase 1 of Drosophila in mutan... | ACCEPT | Summary: Accept. CCS-null mutants show extreme hypersensitivity to paraquat (a redox cycling agent that generates superoxide), demonstrating that Ccs is required for proper oxidative stress response via its role in activating SOD1. Supporting Evidence: PMID:18948262 29E displays the extreme toxic hypersensitivity to the redox cycling agent, paraquat, exhibited by SOD1-null file:DROME/Ccs/Ccs-deep-research-falcon.md CCS-null flies show **paraquat hypersensitivity** essentially equivalent to SOD1-null flies |
| GO:0008340 determination of adult lifespan | IMP PMID:18948262 Instability of superoxide dismutase 1 of Drosophila in mutan... | KEEP AS NON CORE | Summary: Keep as non-core. CCS-null mutants show ~30% reduction in median adult lifespan. However, this is a downstream consequence of SOD1 inactivation rather than a direct molecular function of Ccs. The lifespan phenotype reflects the importance of SOD1 activation for longevity [PMID:18948262 "~30% reduction in the median adult life span"]. Supporting Evidence: PMID:18948262 2008 Oct 23. Instability of superoxide dismutase 1 of Drosophila in mutants deficient for its cognate copper chaperone. file:DROME/Ccs/Ccs-deep-research-falcon.md CCS-null flies show reduced adult survival; the paper describes an approximately **30% reduction in median adult lifespan** compared with controls |
| GO:0016532 superoxide dismutase copper chaperone activity | IDA PMID:18948262 Instability of superoxide dismutase 1 of Drosophila in mutan... | ACCEPT | Summary: Accept as CORE FUNCTION. This is the primary molecular function of Ccs. The study demonstrates that Ccs is required for SOD1 activation and that dCCS can substitute for yeast CCS in activating SOD1. Copper insertion into SOD1 requires CCS domain III cysteines. Supporting Evidence: PMID:18948262 Copper is inserted into the SOD1 apoprotein by a specific chaperone, the copper chaperone for SOD1 (CCS) file:DROME/Ccs/Ccs-deep-research-falcon.md The primary function of Drosophila Ccs is **post-translational activation and stabilization of cytosolic Cu,Zn-SOD1 (dSOD1)**, via copper delivery and associated maturation chemistry; in CCS-null flies, SOD1 activity becomes essentially undetectable and dSOD1 protein is strongly reduced |
| GO:0050821 protein stabilization | IDA PMID:18948262 Instability of superoxide dismutase 1 of Drosophila in mutan... | ACCEPT | Summary: Accept as CORE FUNCTION. Remarkably, CCS-null flies show a striking loss of SOD1 protein (reduced to ~25% of normal), demonstrating that Ccs is required not just for SOD1 activity but for protein stability. This stabilization requires copper insertion and/or disulfide oxidation by Ccs. Supporting Evidence: PMID:18948262 apo-dSOD1 is unusually unstable and ... CCS affords stability to dSOD1 by activating the enzyme through copper insertion and/or disulfide oxidation file:DROME/Ccs/Ccs-deep-research-falcon.md steady-state SOD1 polypeptide is reduced to **~25% of wild-type** |
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