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Reference: Leitch JM, et al. (2009) Activation of Cu,Zn-Superoxide Dismutase in the Absence of Oxygen and the Copper Chaperone CCS. J Biol Chem 284(33):21863-71

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Abstract

Eukaryotic Cu/Zn superoxide dismutases (SOD1s) are generally thought to acquire the essential copper cofactor and intramolecular disulfide bond through the action of the CCS copper chaperone. However, several metazoan SOD1s have been shown to acquire activity in vivo in the absence of CCS, and the Cu/Zn SOD from Caenorhabditis elegans has evolved complete independence from CCS. To investigate SOD1 activation in the absence of CCS, we compared and contrasted the CCS-independent activation of C. elegans and human SOD1 to the strict CCS-dependent activation of S. cerevisiae SOD1. Using a yeast expression system, both pathways were seen to acquire copper derived from cell surface transporters and compete for the same intracellular pool of copper. Like CCS, CCS-independent activation occurs rapidly with a pre-existing pool of apo-SOD1 without the need for new protein synthesis. The two pathways however strongly diverge when assayed for the SOD1 disulfide. SOD1 molecules that are activated without CCS exhibit disulfide oxidation in vivo without oxygen and under copper deplete conditions. The strict requirement for copper, oxygen and CCS in disulfide bond oxidation appears exclusive to yeast SOD1, and we find that a unique proline at position 144 in yeast SOD1 is responsible for this disulfide effect. CCS-dependent and independent pathways also exhibit differential requirements for molecular oxygen. CCS-activation of SOD1 requires oxygen, whereas the CCS-independent pathway is able to activate SOD1s even under anaerobic conditions. In this manner, Cu/Zn SOD from metazoans may retain activity over a wide range of physiological oxygen tensions.

Reference Type
Journal Article
Authors
Leitch JM, Jensen LT, Bouldin SD, Outten CE, Hart PJ, Culotta VC
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