Grant: Project Grant

Deposits of proteins that have formed incorrect ('misfolded') structures are a key feature in many neurodegenerative diseases (NDDs). Strikingly, these misfolded proteins can convert other, correctly folded molecules into the misfolded form and thereby propagate, similar to how infectious prions propagate in "mad cow" disease. However, the mechanism of 'prionlike' conversion is poorly understood-hampering efforts to find effective therapies for NDDs-in part because misfolding and conversion are rare, transient, and involve a mixture of many different structures, making it hard to apply the tools normally used to study protein structures and how they change. One protein that undergoes such conversion is SOD1, whose misfolding is linked to ALS, a fatal motor-neuron disease. We recently developed the first method able to observe SOD1 proteins directly as they misfold and undergo prion-like conversion, using engineered protein constructs wherein a misfolded mutant molecule is tethered to a normal molecule. We will apply this method to determine the conversion mechanism in SOD1, aiming to answer key questions such as: Which parts of the protein are most important for driving conversion or protecting against it? How does the conversion process relate to the 'normal' folding pathways for SOD1? How do disease-linked mutations change conversion, and are these changes related to differences in patient survival times? How do potential drugs affect conversion? How does the single-molecule behaviour relate to propagation at the cellular level? Critically, our approach leverages the unique abilities of our single-molecule assays and relates the single-molecule results to ensemble behaviour, allowing us to overcome the technical challenges hindering the study of prion-like conversion in NDD-linked proteins. This work should lead to significant new insights into the unsolved mechanisms of conversion and identify new therapeutic targets for preventing propagation of misfolding.