Heterodimer formation between superoxide dismutase and its copper chaperone

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Copper, zinc superoxide dismutase (SOD1) requires the copper chaperone for superoxide dismutase (CCS) for in vivo activation.
• The precise molecular mechanisms of CCS-SOD1 interaction and copper ion insertion remain unclear.
• Existing models propose either a heterodimer or a dimer of dimers for CCS-SOD1 complex formation during copper transfer.

Purpose of the Study:

• To investigate the oligomerization state and complex formation between yeast CCS (yCCS) and yeast SOD1 (wtSOD1 and H48F-SOD1 mutant).
• To elucidate the role of zinc and copper loading in yCCS in the formation and stability of the yCCS-SOD1 complex.
• To determine the mechanism of SOD1 activation by yCCS.

Main Methods:

• Gel filtration chromatography
• Dynamic light scattering
• Analytical ultracentrifugation
• Chemical cross-linking experiments
• Enzyme activity assays

Main Results:

• Yeast CCS and a mutant SOD1 (H48F-SOD1) form a stable heterodimeric complex, with no higher-order oligomers detected.
• Heterodimer formation is dependent on zinc but not on the copper loading of yCCS.
• The complex with H48F-SOD1 is more stable than that with wild-type SOD1, suggesting a transient interaction for the latter.
• SOD1 activation by copper-loaded yCCS occurs only in the presence of zinc.

Conclusions:

• The findings strongly support a heterodimeric intermediate model for in vivo copper loading of yeast SOD1 by CCS.
• Zinc plays a critical role in facilitating both heterodimer formation and SOD1 activation.
• The transient nature of the wild-type SOD1 complex suggests efficient copper transfer and subsequent dissociation.