Activation of Cu,Zn-superoxide dismutase in the absence of oxygen and the copper chaperone CCS.
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 Saccharomyces 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 preexisting 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-depleted 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.
Leitch
Jeffry M
JM
Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205.
Jensen
Laran T
LT
Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205.
Bouldin
Samantha D
SD
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208.
Outten
Caryn E
CE
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208.
Hart
P John
PJ
Department of Biochemistry and X-ray Crystallography Core Laboratory, University of Texas Health Science Center, San Antonio, Texas 78229.
Culotta
Valeria C
VC
Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205.
D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism; D003300:Copper / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D010100:Oxygen / Q000737:chemistry*; D010957:Plasmids / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000378:metabolism
C491960:CCS1 protein, S cerevisiae; D004220:Disulfides; D018832:Molecular Chaperones; D029701:Saccharomyces cerevisiae Proteins; D003300:Copper; D013482:Superoxide Dismutase; D010100:Oxygen