Investigating the Stability, Flexibility, and Phase Separation Properties of H46R and H80R Disease Mutants of SOD1: Insights into ALS Pathogenesis.

Human Cu, Zn superoxide dismutase (SOD1) is the primary enzyme in the cellular antioxidant defense system. Mutations in SOD1 are associated with amyotrophic lateral sclerosis (ALS), where protein misfolding and aggregation contribute to the disease pathology. Recently, SOD1 mutants have been shown to undergo phase separation, forming protein-rich droplets that can serve as precursors to the fibrillar aggregates, the pathological hallmarks of ALS. Protein phase separation is a critical process for membraneless organelle formation and the regulation of cellular activities, and its disruption is associated with neurodegeneration. In this study, we investigated two ALS-associated SOD1 mutants, H46R and H80R, and compared them to the wild-type (WT) and Apo forms to elucidate the relationship between phase separation and SOD1's biophysical properties. Using computational studies, chemical denaturation, in vitro condensate formation assays, and analyzing their dynamic behavior, we explored how these mutants influence protein phase separation propensity. Our findings demonstrate that altered secondary structures, stability, and inherent disorder in these mutants directly impact their phase separation behaviors. This study provides new insights into the role of phase separation in ALS pathogenesis and its potential as a therapeutic target.