Mutation/metal deficiency in the "electrostatic loop" enhanced aggregation process in apo/holo SOD1 variants:...

Area of Science:

• Biochemistry
• Neuroscience
• Structural Biology

Background:

• Protein misfolding and aggregation into amyloid fibrils are implicated in various diseases.
• Mutations or disruptions in metal ion homeostasis of superoxide dismutase (SOD1) are linked to Amyotrophic Lateral Sclerosis (ALS).
• The precise role of these factors in SOD1 misfolding and aggregation remains unclear.

Purpose of the Study:

• To investigate the impact of mutation and metal deficiency on SOD1 structural properties and aggregation propensity.
• To elucidate the mechanisms underlying SOD1 misfolding in the context of neurodegenerative diseases.

Main Methods:

• Molecular Dynamics (MD) simulations to model conformational changes.
• Fourier-transform infrared (FTIR) spectroscopy and Dictionary of Secondary Structure in Proteins (DSSP) for structural analysis.
• Thermodynamic studies using Guanidinium hydrochloride (GdnHCl).
• Thioflavin T (ThT) and 8-Anilinonaphthalene-1-sulfonic acid (ANS) fluorescence assays.
• Transmission Electron Microscopy (TEM) for aggregate visualization.

Main Results:

• MD simulations indicated that mutation/metal deficiency alters SOD1 conformation.
• Increased β-sheet structures in apo/holo SOD1 variants suggest aggregation tendency, confirmed by FTIR and DSSP.
• Thermodynamic studies revealed that metal deficiency, mutation, and S-S bond reduction are crucial for SOD1 misfolding.
• Amyloid aggregates formed in apo/holo SOD1 variants under destabilizing conditions, verified by fluorescence and TEM.

Conclusions:

• Mutations in SOD1's electrostatic loop induce structural abnormalities, including altered hydrophobicity and reduced disulfide bonds.
• These structural changes increase SOD1's propensity for denaturation and subsequent amyloid/amorphous aggregate formation.
• The findings support the protein aggregation hypothesis in neurodegenerative diseases like ALS.