| Topic | Key points | Evidence/source |
|---|---|---|
| Identity | The target is **Drosophila melanogaster Ccs**, also identified as **CG17753**, encoding the conserved **copper chaperone for Cu,Zn-superoxide dismutase (SOD1)**; this matches the UniProt context for fruit-fly CCS and distinguishes it from unrelated CCS genes in other organisms. | (pqac-00000001, pqac-00000002) Kirby et al., 2008, *J Biol Chem* 283:35393-35401. DOI/URL: https://doi.org/10.1074/jbc.m807131200 |
| Molecular function | 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. In Drosophila, the primary experimentally supported function is activation/stabilization of SOD1. | (pqac-00000000, pqac-00000002, pqac-00000008) Kirby et al., 2008, https://doi.org/10.1074/jbc.m807131200 |
| Mechanism/domains | Canonical CCS proteins comprise **three domains**: an N-terminal ATX1-like copper-binding domain, a central **SOD1-homology docking domain**, and a C-terminal **CXC motif-containing domain** required for copper insertion/disulfide chemistry. Drosophila CCS is notable because it **lacks the usual domain I CXXC/MXCXXC motif**, yet still functions in SOD1 activation; the **domain III cysteines are required**, as mutation of the CXC motif abolished stabilization of dSOD1 in yeast assays. | (pqac-00000001, pqac-00000004, pqac-00000008, pqac-00000013) Kirby et al., 2008, https://doi.org/10.1074/jbc.m807131200; Rae et al., 2001, *J Biol Chem* 276:5166-5176, https://doi.org/10.1074/jbc.m008005200 |
| Subcellular localization | Direct Drosophila localization evidence was **not retrieved** in the current evidence set. Functionally, Drosophila CCS acts in the **same compartment as cytosolic SOD1**, supported by the CCS-null effect on **cytosolic aconitase** and SOD1 maturation. Broader CCS-family reviews indicate CCS proteins are mainly **cytosolic**, with additional localization to the **mitochondrial intermembrane space (IMS)** in other systems; this should be treated as **family-level inference**, not direct fly-specific proof. | (pqac-00000001, pqac-00000008, pqac-00000009, pqac-00000010, pqac-00000012) Kirby et al., 2008, https://doi.org/10.1074/jbc.m807131200; Kawamata & Manfredi, 2010, *Antioxid Redox Signal* 13:1375-1384, https://doi.org/10.1089/ars.2010.3212; Ge et al., 2019, https://doi.org/10.1007/s10930-019-09824-9 |
| Pathway context | Ccs functions in the **intracellular copper homeostasis/oxidative stress defense pathway**, specifically the branch that matures **Cu,Zn-SOD1**. The pathway relationship is: cellular copper handling → CCS-mediated copper transfer/disulfide maturation → active SOD1 → detoxification of superoxide and protection of cytosolic iron-sulfur enzymes such as aconitase. | (pqac-00000001, pqac-00000002, pqac-00000008, pqac-00000011) Kirby et al., 2008, https://doi.org/10.1074/jbc.m807131200; Rae et al., 2001, https://doi.org/10.1074/jbc.m008005200 |
| Loss-of-function phenotypes | A **CCS-null allele, Ccsn29E**, phenocopies many aspects of SOD1 deficiency: **reduced adult lifespan**, **extreme hypersensitivity to paraquat/oxidative stress**, and **selective loss of cytosolic aconitase activity**. The phenotype is milder than complete Sod1 loss, consistent with **limited CCS-independent activation** of fly SOD1. | (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000005, pqac-00000014) Kirby et al., 2008, https://doi.org/10.1074/jbc.m807131200 |
| Quantitative readouts | In CCS-null flies, **SOD1 activity was not detectable** by standard assays, while **steady-state SOD1 polypeptide fell to ~25% of normal**. **Cytosolic aconitase activity decreased by ~50%**, whereas mitochondrial aconitase was unaffected. Median adult lifespan was reduced by **~30% relative to control** in one summary, and the residual activity in CCS-null flies was sufficient to extend lifespan to **~30 days beyond the ~10-day median of SOD1-null mutants**. Paraquat assays used **2 mM paraquat**, with **≥200 flies/genotype** in some tests and **survivors scored after 24 h**. | (pqac-00000000, pqac-00000001, pqac-00000005, pqac-00000014) Kirby et al., 2008, https://doi.org/10.1074/jbc.m807131200 |
| Cross-species observations | Drosophila CCS shows **species-specific behavior**: it activates **Drosophila SOD1** well and is **nearly as effective as yeast CCS on human SOD1**, but is comparatively poor at activating **yeast SOD1**. Conversely, **human SOD1 expressed in CCS-null flies remains robustly active** and rescues lifespan/oxidative-stress defects, highlighting stronger **CCS-independent activation capacity** for human than endogenous fly SOD1 in this model. | (pqac-00000000, pqac-00000002, pqac-00000005, pqac-00000013, pqac-00000014) Kirby et al., 2008, https://doi.org/10.1074/jbc.m807131200 |


*Table: This table summarizes the experimentally supported functional annotation of Drosophila melanogaster Ccs/CG17753, emphasizing molecular role, mechanism, pathway placement, localization evidence, and phenotypic consequences of loss. It is useful as a compact evidence map tied directly to retrieved primary and review sources.*