Syntaxin SNARE hypothesis

Serotypes B, D, E, and G cleave different sites on the synaptic vesicle protein, synaptobrevin (VAMP), whereas serotypes A and E cleave the presynaptic membrane-associated protein SNAP-25 (Schiavo et al., 2000 Simpson, 2004). Serotype Cl is unique in that it cleaves two cytoplasmic proteins, syntaxin and SNAP-25 (Wiltiamson et al., 1996). Interaction of these SNAREs on the surface of synaptic vesicles and active zone membranes is required for voltage- and Ca " -dependent release of neurotransmitter cleavage by BoNT inhibits this process, leading to muscle weakness and paralysis (Sutton et al., 1998 Schiavo et al., 2000). Cleavage of SNARE proteins appears to be sufficient to account for all actions of the BoNTs, and the SNARE hypothesis has received near universal acceptance since its introduction in the early 1990s. 

Amperometry at single PC 12 cells has also been used in conjunction with a genetic cell transfection protocol to examine the effects of toxin expression on basal and evoked exocytosis. PC 12 cells have been transfected with the specific endoprotease Botulinum neurotoxin Cl light chain (BoNT/Cl), which cleaves the proteins syntaxin and SNAP-25 [5], The molecular dissection of the mechanisms underlying exocytosis has been motivated by the SNARE hypothesis, which postulates that exocytosis requires the assembly of the plasma membrane proteins syntaxin 1, SNAP-25, and the vesicle associated membrane protein (VAMP) into a complex [5], This SNARE complex then acts as a receptor for cytosolic components of the proposed fusion machinery. Direct evidence for the role of the SNARE proteins in neurotransmission comes from molecular genetic studies in which syntaxin and VAMP have been shown to be required for neurotransmission in Drosophila [47 9] and Caenorhabditis elegans [50,51]. To assess the effects of the disruption of SNARE proteins on exocytosis in PC 12 cells, amperometry has been used in conjunction with a genetic cell transfection assay to establish a... 

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