Distinct amyloid fibril structures formed by ALS-causing SOD1 mutants G93A and D101N

Two hundred eight genetic mutations in SOD1 have been linked to amyotrophic lateral sclerosis (ALS). Of these, the G93A and D101N variants maintain much of their physiological function, closely resembling that of wild-type SOD1, and the SOD1-G93A transgenic mouse is the most extensively used mouse line in the study of ALS. In this study, we report two cryo-EM structures of amyloid fibrils formed by G93A and D101N mutants of SOD1 protein. These mutations give rise to amyloid fibrils with distinct structures compared to native SOD1 fibrils. The fibril core displays a serpentine configuration featuring four β-strands, held together by two hydrophobic cavities and a salt bridge between Arg143 and Asp96 in the G93A fibril, and by a hydrophobic cavity and a salt bridge between Arg143 and Asp132 in the D101N fibril, demonstrating unique structural features for each mutant. Moreover, our results show that G93A fibrils are significantly more toxic than those formed by D101N, which do not show a marked increase in toxicity compared to wild-type SOD1 fibrils. This study sheds light on the structural mechanisms through which SOD1 mutants aggregate and induce cytotoxicity in ALS.