Mechanisms for activating Cu- and Zn-containing superoxide dismutase in the absence of the CCS Cu chaperone.
The Cu- and Zn-containing superoxide dismutase 1 (SOD1) largely obtains Cu in vivo by means of the action of the Cu chaperone CCS. Yet, in the case of mammalian SOD1, a secondary pathway of activation is apparent. Specifically, when human SOD1 is expressed in either yeast or mammalian cells that are null for CCS, the SOD1 enzyme retains a certain degree of activity. This CCS-independent activity is evident with both wild-type and mutant variants of SOD1 that have been associated with familial amyotrophic lateral sclerosis. We demonstrate here that the CCS-independent activation of mammalian SOD1 involves glutathione, particularly the reduced form, or GSH. A role for glutathione in CCS-independent activation was seen with human SOD1 molecules that were expressed in either yeast cells or immortalized fibroblasts. Compared with mammalian SOD1, the Saccharomyces cerevisiae enzyme cannot obtain Cu without CCS in vivo, and this total dependence on CCS involves the presence of dual prolines near the C terminus of the SOD1 polypeptide. Indeed, the insertion of such prolines into human SOD1 rendered this molecule refractory to CCS-independent activation. The possible implications of multiple pathways for SOD1 activation are discussed in the context of SOD1 evolutionary biology and familial amyotrophic lateral sclerosis.
Carroll
Mark C
MC
Department of Environmental Health Sciences, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD 21218, USA.
Girouard
Jody B
JB
Ulloa
Janella L
JL
Subramaniam
Jamuna R
JR
Wong
Phillip C
PC
Valentine
Joan Selverstone
JS
Culotta
Valeria Cizewski
VC
D000818:Animals; D002460:Cell Line; D003300:Copper / Q000737:chemistry*; D004789:Enzyme Activation; D005978:Glutathione / Q000378:metabolism; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism / Q000502:physiology*; D009154:Mutation; D029701:Saccharomyces cerevisiae Proteins; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015032:Zinc / Q000737:chemistry*
C491960:CCS1 protein, S cerevisiae; C491962:Ccs protein, mouse; D018832:Molecular Chaperones; D029701:Saccharomyces cerevisiae Proteins; D003300:Copper; D013482:Superoxide Dismutase; D005978:Glutathione; D015032:Zinc