ALS-causing SOD1 mutations H46R and G85R form similar novel amyloid fibril structures and promote ferroptosis in cells

More than two hundred genetic mutations of Cu, Zn-superoxide dismutase (SOD1) have been identified in amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by the selective death of motor neurons through ferroptosis. Two ALS-causing SOD1 mutations, H46R and G85R, are metal-binding region mutants with reduced affinity for metal ions. Here, we generated amyloid fibrils from the apo forms of H46R and G85R under reducing conditions and determined their structures using cryo-EM. We built models for the fibril cores, comprising residues 85-153 for H46R and 82-153 for G85R. These mutations disrupt crucial interactions in the wild-type SOD1 fibril, resulting in amyloid fibrils with distinct structures compared to the wild-type fibril. Remarkably, H46R and G85R form similar novel amyloid fibril structures. The fibril cores display a serpentine fold containing seven or eight {beta}-strands, which are stabilized by a hydrophobic cavity. In the G85R fibril core, Arg85 and Asp101 form a salt bridge for stabilization. We demonstrate that fibril seeds from H46R and G85R cause more severe mitochondrial impairment and significantly promote ferroptosis in neuronal cells, compared with those from wild-type SOD1. Our findings reveal how different SOD1 mutations can result in similar amyloid fibril structures and contribute to ALS pathology.