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Neurourol Urodyn. 2014 Jul;33 Suppl 3:S14-20. doi: 10.1002/nau.22634.

Chapter 3: Molecular basis for the therapeutic effectiveness of botulinum neurotoxin type A.

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  • 1International Centre for Neurotherapeutics, Dublin City University, Glasnevin, Dublin, Ireland.

Abstract

The utility of botulinum neurotoxin type A (BoNT/A) for treating overactive muscles and endocrine glands is attributable to a unique conflation of properties honed to exploit and inactivate synaptic transmission. Specific, high-affinity coincident binding to gangliosides plus an intraluminal loop of synaptic vesicle protein 2 (SV2) by the heavy chain (HC) of BoNT/A confers selectivity for presynaptic nerve terminals and subsequent uptake by endocytosis. Upon vesicle acidification, the HC forms a channel for transmembrane transfer of the light chain to the cytosol, as observed by single channel recordings. The light chain is a Zn(2+) -dependent endoprotease that cleaves and inactivates SNAP-25, thereby blocking exocytotic release of transmitters, a discovery that revealed the pivotal role of the latter in synaptic vesicle fusion. A di-leucine motif in BoNT/A light chain stabilizes this protease, contributing to its longevity inside nerves. The ubiquity of SV2 and SNAP-25 has prompted re-evaluation of the nerve types susceptible to BoNT/A. In urology, there is emerging evidence that BoNT/A blocks neuropeptide release from afferent nerves, exocytosis of acetylcholine and purines from efferent nerves, and possibly ATP release from the urothelium. Suppression by BoNT/A of the surface expression of nociceptor channels on bladder afferents might also contribute to its improvement of urological sensory symptoms.

© 2014 Wiley Periodicals, Inc.

KEYWORDS:

P2X3; SNAP-25; SV2; TRPV1; cholinergic; exo-/endocytosis; purinergic; transmitters

PMID:
25042137
[PubMed - indexed for MEDLINE]
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