A molecular basis underlying differences in the toxicity of botulinum serotypes A and E.
Botulinum neurotoxins (BoNTs) block neurotransmitter release through their specific proteolysis of the proteins responsible for vesicle exocytosis. Paradoxically, two serotypes of BoNTs, A and E, cleave the same molecule, synaptosome-associated protein with relative molecular mass 25K (SNAP-25), and yet they cause synaptic blockade with very different properties. Here we compared the action of BoNTs A and E on the plasma membrane fusion machinery composed of syntaxin and SNAP-25. We now show that the BoNT/A-cleaved SNAP-25 maintains its association with two syntaxin isoforms in vitro, which is mirrored by retention of SNAP-25 on the plasma membrane in vivo. In contrast, BoNT/E severely compromises the ability of SNAP-25 to bind the plasma membrane syntaxin isoforms, leading to dissociation of SNAP-25. The distinct properties of botulinum intoxication, therefore, can result from the ability of shortened SNAP-25 to maintain its association with syntaxins-in the case of BoNT/A poisoning resulting in unproductive syntaxin/SNAP-25 complexes that impede vesicle exocytosis.
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
Mark
M
Bajohrs
Colin
C
Rickman
Thomas
T
Binz
Bazbek
B
Davletov
D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D001905:Botulinum Toxins / Q000737:chemistry* / Q000235:genetics; D019274:Botulinum Toxins, Type A / Q000737:chemistry* / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000378:metabolism; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000378:metabolism; D016716:PC12 Cells; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms; D050765:Qa-SNARE Proteins; D051381:Rats; D013569:Synapses; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1
D000954:Antigens, Surface; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D050765:Qa-SNARE Proteins; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D005982:Glutathione Transferase; D001905:Botulinum Toxins; D019274:Botulinum Toxins, Type A; C096326:botulinum toxin type E