Atomic structure of a toxic, oligomeric segment of SOD1 linked to amyotrophic lateral sclerosis (ALS).
More than 170 mutations in superoxide dismutase 1 (SOD1) are linked to inherited forms of ALS, and aggregates of this protein are a pathological feature associated with this disease. Although it is accepted that SOD1 gains a toxic function in the disease state, a molecular understanding of the toxic species is lacking. Here, we identify a short segment of SOD1 that is both necessary and sufficient for toxicity to motor neurons. The crystal structure of the segment reveals an out-of-register β-sheet oligomer, providing a structural rationale for the toxic effects of mutant SOD1 in ALS.
Fibrils and oligomers are the aggregated protein agents of neuronal dysfunction in ALS diseases. Whereas we now know much about fibril architecture, atomic structures of disease-related oligomers have eluded determination. Here, we determine the corkscrew-like structure of a cytotoxic segment of superoxide dismutase 1 (SOD1) in its oligomeric state. Mutations that prevent formation of this structure eliminate cytotoxicity of the segment in isolation as well as cytotoxicity of the ALS-linked mutants of SOD1 in primary motor neurons and in a Danio rerio (zebrafish) model of ALS. Cytotoxicity assays suggest that toxicity is a property of soluble oligomers, and not large insoluble aggregates. Our work adds to evidence that the toxic oligomeric entities in protein aggregation diseases contain antiparallel, out-of-register beta-sheet structures and identifies a target for structure-based therapeutics in ALS.