Inhibiting the formation of ALS-relevant SOD1 oligomers

Proctor, Elizabeth Anne

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March 19, 2019

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Proctor, Elizabeth Anne
- Affiliation: School of Medicine, Department of Biochemistry and Biophysics

Abstract

Amyotrophic Lateral Sclerosis (ALS) is an invariably fatal neurodegenerative disease selectively affecting motor neurons. The aggregation of Cu, Zn superoxide dismutase (SOD1) has been linked to the disease, but the toxic species and mechanism of disease progression remain unknown. In this work, we explore two strategies for interfering in SOD1 aggregation: preventing the dissociation of the native homodimer, and preventing the association of misfolded SOD1 monomers into potentially toxic oligomers. In the first strategy, we elucidate the mechanism by which a commonly found post-translational modification, glutathionylation, increases the dissociation of native SOD1. We find that the addition of glutathione moieties at their modification site near the dimer interface creates steric clashing that causes the two monomers to twist in relation to one another, changing the shape and size of the dimer interface. These changes to the dimer interface cause a decoupling of dimerization and monomer folding processes, which in turn stabilizes a folding intermediate on the path to dimer dissociation, increasing the population of SOD1 monomer as observed in experiments. To pursue our second strategy, we develop a method to model the structure of meta-stable protein aggregation intermediates, which have been implicated as toxic species in ALS. We incorporate experimental data from limited proteolysis with computational techniques to obtain the first-ever structural model of a meta-stable protein oligomer, a SOD1 trimer isolated in our laboratory that is recognized by conformational antibodies shown to bind disease-relevant misfolded SOD1 species. We use our structure to design mutations that will stabilize or destabilize the formation of SOD1 trimer in vitro, and demonstrate using time-resolved analytical size exclusion chromatography that the majority of our designed mutants exhibit the aggregation behavior that we predict.

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