[BXA2_CLOBO] Inhibits acetylcholine release. The botulinum toxin binds with high affinity to peripheral neuronal presynaptic membrane to the secretory vesicle protein SV2. It binds directly to the largest luminal loop of the three isoforms SV2A, SV2B and SV2C. It is then internalized by receptor-mediated endocytosis. The C-terminus of the heavy chain (H) is responsible for the adherence of the toxin to the cell surface while the N-terminus mediates transport of the light chain from the endocytic vesicle to the cytosol. After translocation, the light chain (L) hydrolyzes the '197-Gln-|-Arg-198' bond in SNAP-25, thereby blocking neurotransmitter release. Inhibition of acetylcholine release results in flaccid paralysis, with frequent heart or respiratory failure (By similarity).
Evolutionary Conservation
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Publication Abstract from PubMed
Clostridium botulinum neurotoxins (BoNTs), the most potent toxins known, disrupt neurotransmission through proteolysis of proteins involved in neuroexocytosis. The light chains of BoNTs are unique zinc proteases that have stringent substrate specificity and require exceptionally long substrates. We have determined the crystal structure of the protease domain from BoNT serotype A (BoNT/A). The structure reveals a homodimer in a product-bound state, with loop F242-V257 from each monomer deeply buried in its partner's catalytic site. The loop, which acts as a substrate, is oriented in reverse of the canonical direction for other zinc proteases. The Y249-Y250 peptide bond of the substrate loop is hydrolyzed, leaving the Y249 product carboxylate coordinated to the catalytic zinc. From the crystal structure of the BoNT/A protease, detailed models of noncanonical binding and proteolysis can be derived which we propose are also consistent with BoNT/A binding and proteolysis of natural substrate synaptosome-associated protein of 25 kDa (SNAP-25). The proposed BoNT/A substrate-binding mode and catalytic mechanism are markedly different from those previously proposed for the BoNT serotype B.
Crystal structure of Clostridium botulinum neurotoxin protease in a product-bound state: Evidence for noncanonical zinc protease activity.,Segelke B, Knapp M, Kadkhodayan S, Balhorn R, Rupp B Proc Natl Acad Sci U S A. 2004 May 4;101(18):6888-93. Epub 2004 Apr 23. PMID:15107500[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
↑Segelke B, Knapp M, Kadkhodayan S, Balhorn R, Rupp B. Crystal structure of Clostridium botulinum neurotoxin protease in a product-bound state: Evidence for noncanonical zinc protease activity. Proc Natl Acad Sci U S A. 2004 May 4;101(18):6888-93. Epub 2004 Apr 23. PMID:15107500 doi:10.1073/pnas.0400584101
