Elucidating the basis for ubiquitination of misfolded ALS proteins by E3 ligase Enzymes
A pathologic feature in both sporadic and familial ALS patients is the presence of large neuronal inclusions enriched with misfolded proteins, including SOD1, TDP43 and FUS that are frequently modified with the small protein ubiquitin (Ub). This observation, also common to Parkinson’s disease, indicates impairment in the ubiquitin-proteasome system that is responsible for labeling misfolded proteins with Ub, funneling them to the 26S proteasome for degradation, and maintaining neuron health.
In this proposal we aim to identify enzymes in the ubiquitination pathway that are the root cause of inefficient misfolded protein ubiquitination leading to the formation of inclusions. We will focus on three E3 ligase enzymes – Dorfin (RNF19a), Parkin and NEDL1 that have been shown to ubiquitinate ALS-associated proteins including SOD1 or TDP-43. We propose that these E3 ligases differentially ubiquitinate folded vs misfolded ALS proteins leading to aberrant sites of ubiquitination and incorrect Ub chain types and lengths on the misfolded proteins. This leads to poor recognition by Ub adapter proteins that shuttle the ubiquitinated substrates to the 26S proteasome and results in toxic conformer accumulation. We aim to identify the basis for Dorfin auto-inhibition to show its ubiquitination activity is amplified towards misfolded ALS-associated proteins. This mode of regulation was shown by us for Parkin in 2011 and has now sparked therapeutic development for Parkinson’s disease by several biotechnology companies. We believe the same potential exists for Dorfin, or other E3 ligases, and our approaches to uncover how these enzymes contribute to impaired protein degradation in ALS are the starting point to new therapeutics for all ALS patients.
Gary Shaw , University of Western Ontario
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