The hallmark feature of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), is the accumulation of cytoplasmic inclusions of key disease-linked proteins. Two of these proteins, TDP-43 and SOD1, represent a significant proportion of sporadic and familial ALS cases, respectively. The population of potentially aggregation-prone partially-folded states on the folding free-energy landscape may serve as a common mechanism for ALS pathogenesis. A detailed biophysical understanding of the folding and misfolding energy landscapes of TDP-43 and SOD1 can provide critical insights into the design of novel therapeutics to delay onset and progression in ALS.

Equilibrium unfolding studies on the RNA recognition motif (RRM) domains of TDP-43 revealed the population of a stable RRM intermediate in RRM2, with residual structure localized to the N-terminal half of the domain. Other RRM domains from FUS/TLS and hnRNP A1 similarly populate RRM intermediates, suggesting a possible connection with disease. Mutations, which enhance the population of the RRM2 intermediate, could serve as tools for deciphering the functional and misfolding roles of this partially-folded state in disease models, leading to the development of new biomarkers to track ALS progression.

ALS mutations in SOD1 have been shown to destabilize the stable homodimer to result in increased populations of the monomeric and unfolded forms of SOD1. Mechanistic insights into the misfolding of SOD1 demonstrated that the unfolded state is a key species in the initiation and propagation of aggregation, suggesting that limiting these populations may provide therapeutic benefit to ALS patients. An in vitro time-resolved Förster Resonance Energy Transfer assay to screen small molecules that stabilize the native state of SOD1 has identified several lead compounds, providing a pathway to new therapeutics to treat ALS.