Wild-type Cu/Zn superoxide dismutase stabilizes mutant variants by heterodimerization

Area of Science:

• Biochemistry
• Neuroscience
• Molecular Biology

Background:

• Mutations in Cu/Zn superoxide dismutase (SOD1) cause a subset of amyotrophic lateral sclerosis (ALS).
• Wild-type SOD1 (SOD(WT)) can form heterodimers with mutant SOD1, reducing aggregation but retaining toxicity.
• The exact toxic mechanisms of mutant SOD1, particularly in dimerized forms, remain unclear.

Purpose of the Study:

• To investigate the biochemical and biophysical properties of obligate SOD1 dimers.
• To determine the impact of forced heterodimerization on SOD1 mutant properties and activity.
• To assess the contribution of soluble, active SOD1 dimers to mutant SOD1 toxicity.

Main Methods:

• Construction and analysis of obligate SOD1 dimers linked by a peptide.
• Circular dichroism spectroscopy to assess protein folding and structure.
• Proteolytic degradation assays to evaluate protein stability.
• Antibody binding assays to detect misfolded SOD1.
• Enzyme activity assays to measure dismutase function.

Main Results:

• SOD1 mutants exhibited increased unstructured residues, indicating altered folding.
• SOD(WT) stabilized heterodimers, enhancing resistance to proteolysis compared to mutant homodimers.
• Heterodimerization decreased the binding of mutant SOD1 to antibodies targeting misfolded forms.
• Obligate SOD1 dimers, including the labile SOD1(G85R) mutant, displayed significant dismutase activity.

Conclusions:

• Soluble, dismutase-active SOD1 dimers may contribute to the toxicity observed in mutant SOD1-linked ALS.
• Forced dimerization influences SOD1 folding, stability, and antibody recognition.
• These findings suggest that the enzymatic activity of soluble SOD1 dimers is a relevant factor in ALS pathogenesis.