A methyl arginine targeting chimera for the lysosomal degradation of intracellular proteins

PROJECT SUMMARY/ABSTRACT Targeted-protein degradation (TPD) is a novel modality that harnesses cellular proteolysis to eliminate disease-causing proteins. Proteolysis-targeting chimeras (PROTACs) are small molecule degraders that induce proximity of the proteasomal machinery with a substrate. Such approaches hold the promise to revolutionize modern medicine as they target classically undruggable families that lack active sites and offer safer therapeutic windows due to their catalytic pharmacology. However, PROTACs are limited by the capacity of proteasomes. A multi-step assembly of ubiquitin ligases precedes POI ubiquitination, further complicating degrader design and efficacy. Additional challenges include acquired lysine mutations, a small fraction of available E3 ligases, and an inability to effectively troubleshoot the events leading up to proteasomal degradation. Thus, several limitations must be addressed before the potential of degrader modalities can be fully realized. Lysosomes are the alternative degradative route and have been exploited for extracellular proteins by Lysosomal Targeting Chimeras (L YTACs). These exciting developments highlight the potential of lysosomes to combat the central limitations of proteasomal degraders, but are wholly restricted to extracellular proteins. Degraders of intracellular proteins rely on ubiquitin modifications that direct proteins to proteasomes. Recent work shows that arginine methylation modifications direct proteins to lysosomes during normal homeostatic maintenance in unmodified, natural conditions. Preliminary work shows that this pathway can be activated through proximity between a substrate and a protein arginine methyltransferase. We hypothesize that chemically inducing arginine methylation will be sufficient to target diverse protein classes for degradation in lysosomes. The proposal's main goals are to characterize the mechanisms for applying this degradation route synthetically (Aim 1) and to identify endogenous substrates of this degradation pathway that may later be amenable to synthetic degradation (Aim 2). The outcome of this study will generate a degrader modality that is independent of ubiquitin and offer insight into endogenous networks of protein homeostasis. This research holds long-term potential to improve therapeutic tractability across diverse disease states.