Copper Chaperone-Dependent and -Independent Activation of Three Copper-Zinc Superoxide Dismutase Homologs Localized in Different Cellular Compartments in Arabidopsis
Date Issued
2012
Date
2012
Author(s)
Huang, Chien-Hsun
Abstract
Superoxide dismutases (SODs) are enzymes that protect cells from oxidative damage. The major pathway for CuZnSOD activation involves the function of a Copper Chaperone for SOD (CCS), whereas an additional, minor CCS-independent pathway that has been observed in mammals. Through overexpression of three Arabidopsis CuZnSOD genes (CSDs) in yeast and Arabidopsis protoplasts, we demonstrate the existence of a CCS-independent activation pathway in Arabidopsis thaliana. Interestingly, the three Arabidopsis CSDs show strongly different preference for the two activation pathways: the main activation pathway for CSD1 in the cytoplasm involved a CCS-dependent and -independent pathway, which was similar to that for human CSD. Activation of CSD2 in chloroplasts depended totally on CCS similar to yeast (Saccharomyces cerevisiae) CSD. Peroxisome-localized CSD3 via a CCS-independent pathway was similar to nematode (Caenorhabditis elegans) CSD in retaining activity in the absence of CCS. The residual SOD activity detected in AtCCS knockout plants is sufficient for seed germination and root growth, confirming that this alternative pathway is physiologically functional. Through a series of glutathione manipulation experiments, we further confirmed that glutathione plays a role in CCS-independnet pathway but must cooperate with an unknown factor for SOD activation. According to previous publications and our finding, two models of the CCS-independent mechanism are proposed. We also suggest that the CSD protein conformation at C-terminal is important in providing a docking site for unknown factor to interact with. Our findings reveal a complex system underlying CSD activation which ensures a highly specific and sophisticated regulation of antioxidant pathways in plants and has not been reported in other organisms. However, the clear and definite mechanism needs further investigation.
Subjects
CuZnSOD CCS-independent activation
Type
thesis
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