Mutant SOD1 instability: implications for toxicity in amyotrophic lateral sclerosis

Area of Science:

• Biochemistry
• Neuroscience
• Molecular Biology

Background:

• Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with an incompletely understood biological basis for motor neuron degeneration.
• Mutant variants of copper-zinc superoxide dismutase (SOD1) are implicated in familial ALS, with over 100 identified since 1993.
• Linking cellular stresses, aging, and mutant SOD1 toxicity to motor neuron death is a critical research challenge.

Purpose of the Study:

• To compare the physicochemical properties of wild-type and mutant SOD1 proteins.
• To identify specific vulnerabilities in mutant SOD1 that may contribute to toxicity in vivo.
• To elucidate the structural and functional changes associated with SOD1 mutations relevant to ALS pathogenesis.

Main Methods:

• X-ray crystallography was used to determine the structures of metallated wild-type-like (WTL) SOD1 mutants.
• Physicochemical properties of wild-type and mutant SOD1 proteins were compared.
• Susceptibility of SOD1 variants to disulfide bond reduction and metal loss was assessed.

Main Results:

• Metallated WTL SOD1 mutants exhibit near-native structures with subtle backbone fold changes.
• Metal-binding region (MBR) SOD1 mutants, deficient in copper and zinc, show severe thermal destabilization and structural disorder.
• WTL SOD1 mutants are more susceptible to disulfide bond reduction, leading to metal loss and monomerization, resembling MBR mutants.

Conclusions:

• Partially unfolded and metal-deficient SOD1 species, arising from disulfide bond cleavage or inherent MBR mutations, are key toxic intermediates.
• Disordered loops and monomeric SOD1 structures are prone to aberrant self-association and detrimental interactions.
• Further research is needed to connect these abnormal SOD1 properties to specific mechanisms of motor neuron toxicity in ALS.