A biological PROTAC for α-synuclein

The accumulation of misfolded and aggregation-prone proteins is the hallmark of neurodegenerative diseases such as Parkinson’s disease and amyotrophic lateral sclerosis (ALS). α-Synuclein aggregation drives Parkinson’s disease pathology, and is a suitable target for selective protein clearance. Biological proteolysis targeting chimeras (bioPROTACs) aim to eliminate disease-causing intracellular proteins using host cell ubiquitination and degradation functions. Here, we describe a bioPROTAC comprising the E3 ubiquitin ligase domain of CHIP (carboxy terminus of Hsc70-interacting protein) fused to NbSyn87, a nanobody specific for α-synuclein. Co-expression with α-synuclein resulted in a significant decrease in the abundance or complete degradation of both wild-type and Parkinson’s disease-associated mutant α-synuclein (A53T, A53V, and G51D) dependent on cell type. The bioPROTAC also significantly reduced abundance of insoluble α-synuclein aggregates. In contrast, CHIP-based bioPROTACs targeting superoxide dismutase 1 (SOD1) or LIM domain only 2 (LMO2) failed to degrade their targets and in some instances, increased target abundance due to stabilising interactions with the recognition domain. These findings demonstrate key parameters for consideration during BioPROTAC design including target half-life, bioPROTAC solubility, recognition domain binding affinity, molecular chaperone activity, and interdomain linker optimisation. This work demonstrates the use of CHIP-based bioPROTACs for therapeutic degradation of α-synuclein in the synucleinopathies and provides insights for future targeted degrader development.