Design and synthesis of modular proteolysis targeting chimeras (PROTACs) for the degradation of Clostridium botulinum type A neurotoxin (BoNT/A)

Botulinum neurotoxins (BoNTs) are the most potent toxins known and can be easily produced and isolated in large amount, so that they are considered potential bioterrorism agents. BoNTs are metalloproteases of bacterial origin that enter the neuromuscular junction and block the release of the neurotransmitter acetylcholine causing a life-threatening neuromuscular paralysis known as botulism. To date, there are no effective treatments able to efficiently block the action of the toxin once it has entered the target neurons. Acetylcholine is physiologically delivered through a process of exocytosis which sees involved the SNARE protein complex which govern membrane fusion. BoNTs bind to SNARE proteins and carry out a proteolytic action that prevents the normal release of the neurotransmitter. The aim of this project is to develop a BoNT-specific PROteolysis TArgeting Chimera (PROTAC) system composed by i) pomalidomide, a ligand for the neuronal E3-ubiquitin ligase cereblon, ii) a high-affinity binder of the BoNT metalloprotease, and iii) a linker that joins the two ends in order to hijack the endogenous ubiquitin–proteasome system selectively against the BoNT metalloprotease and to test its ability to accelerate toxin degradation inside neurons to quicken the recovery from neuromuscular paralysis.