A gain of superoxide dismutase (SOD) activity obtained with CCS, the copper metallochaperone for SOD1

The incorporation of copper ions into the cytosolic superoxide dismutase (S OD1) is accomplished in vivo by the action of the copper metallochaperone C CS (popper chaperone for SOD1), Mammalian CCS is comprised of three distinc t protein domains, with a central region exhibiting remarkable homology (ap proximately 50% identity) to SOD1 itself, Conserved in CCS are all the SOD1 zinc binding ligands and three of four histidine copper binding ligands, I n CCS the fourth histidine is replaced by an aspartate (Asp(200)). Despite this conservation of sequence between SOD1 and CCS, CCS exhibited no detect able SOD activity, Surprisingly, however, a single D200H mutation, targetin g the fourth potential copper ligand in CCS, granted significant superoxide scavenging activity to this metallochaperone that was readily detected wit h CCS expressed in yeast. This mutation did not inhibit the metallochaperon e capacity of CCS, and in fact, D200H CCS appears to represent a bifunction al SOD that can self-activate itself with copper. The aspartate at CCS posi tion 200 is well conserved among mammalian CCS molecules, and we propose th at this residue has evolved to preclude deleterious reactions involving cop per bound to CCS.