Pharmacology of Botulinum Neurotoxins: Exploitation of Their Multifunctional Activities as Transmitter Release Inhibitors and Neuron-Targeted Delivery Vehicles

S. V. Ovsepian () · J. O. Dolly · V. B. O’Leary · G. W. Lawrence International Centre for Neurotherapeutics, Dublin City University, Dublin, Ireland Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE), Ludwig-Maximilians-Universität München, München, Germany e-mail: [email protected] and [email protected] Abstract Quantal transmitter release from nerves is inhibited by all seven serotypes (A–G) of botulinum neurotoxin (BoNT), with some subtle but functional differences. Commonalities and dissimilarities in these proteins, and new recombinant forms, are highlighted in terms of their multiple activities and domains responsible for binding to the neuronal acceptors, subsequent endocytosis, translocation and proteolytic inactivation of intracellular soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs) culminating in the blockade of neuro-exocytosis lasting for weeks or months. The neurotoxins bind to dual acceptors, gangliosides and intra-lumenal regions of vesicular proteins, and co-traffic into neurons. Subsequently, their proteases pass to the cytosol via a channel created in the endosomal limiting membrane and cleave distinct bonds in the substrate SNARE(s). Modification of these targets is responsible for their characteristic pharmacological activities. The prolonged duration of type A seems attributable to an identified stabilisation motif that extends the longevity of its protease. BoNTs have proved instrumental in deciphering a molecular basis for regulated exocytosis; now, emerging knowledge is helping to explain why synchronisation of released quanta of transmitter is perturbed by certain serotypes (/B, /D and /F) and not others (/A, /C1 and /E). Novel chimeras created by protein engineering are endowed with advantageous features of two serotypes for targeting sensory neurons and alleviating inflammatory pain (LC/E-BoTIM/A). Likewise, an innocuous mutant of /B (BoTIM/B) fused to core streptavidin (CS-BoTIM/B) has been exploited for guiding molecular cargo and viral vectors into nerve cells. These novel discoveries exemplify the versatility of BoNT in targeting and delivering therapeutics into neurons.