Botulinum toxin causes flaccid paralysis by inhibiting neurotransmitter (acetylcholine) release from the presynaptic membranes of nerve terminals of eukaryotic host skeletal and autonomic nervous system, with frequent heart or respiratory failure. Precursor of botulinum neurotoxin X which has 2 coreceptors; complex polysialylated gangliosides found on neural tissue and specific membrane-anchored proteins found in synaptic vesicles. Receptor proteins are exposed on host presynaptic cell membrane during neurotransmitter release, when the toxin heavy chain (HC) binds to them. Upon synaptic vesicle recycling the toxin is taken up via the endocytic pathway. When the pH of the toxin-containing endosome drops a structural rearrangement occurs so that the N-terminus of HC forms pores that allows the light chain (LC) to translocate into the cytosol. Once in the cytosol the disulfide bond linking the 2 subunits is reduced and LC cleaves its target protein on synaptic vesicles, preventing their fusion with the cytoplasmic membrane and thus neurotransmitter release (By similarity). Artificially assembled BoNT/X cleaves synaptobrevin-2/VAMP2 and VAMP4 in cultured rat neurons and causes flaccid paralysis in mice (PubMed:28770820). Has proteolytic activity. After translocation into the eukaryotic host cytosol, LC hydrolyzes the '66-Arg-|-Ala-67' bond in synaptobrevin-2/VAMP2, and the equivalent bonds in 'Arg-|-Ala' bonds in VAMP1 and VAMP3, thus blocking neurotransmitter release (PubMed:28770820). Has a wider target range than most BoNTs, as it also cleaves the '87-Arg-|-Ser-89' bond in VAMP4, the '40-Arg-|-Ser-41' bond in VAMP5 and the '173-Lys-|-Ser-174' bond in YKT6; whether these are physiologically relevant substrates is unknown (PubMed:28770820). BoNT/X is 10-fold more efficient than BoNT/B and 40-fold more efficient than TeTX on an artificial human VAMP1 substrate (PubMed:29540745). Responsible for epithelial cell transcytosis, host nerve cell targeting and translocation of light chain (LC) into host cytosol. Composed of 3 subdomains; the translocation domain (TD), and N-terminus and C-terminus of the receptor-binding domain (RBD). The RBD is responsible for the adherence of the toxin to the cell surface. It simultaneously recognizes 2 coreceptors; polysialated gangliosides and an unknown receptor protein in close proximity on host synaptic vesicles. The N-terminus of the TD wraps an extended belt around the perimeter of the LC, protecting Zn(2+) in the active site (By similarity). The TD inserts into synaptic vesicle membrane to allow translocation into the host cytosol (By similarity). Protein ligation of the RBD to the rest of the toxin (creates an artificial whole toxin) greatly increases VAMP2 degradation, and thus neuron uptake (PubMed:28770820). Limited hydrolysis of proteins of the neuroexocytosis apparatus, synaptobrevins, SNAP25 or syntaxin. No detected action on small molecule substrates. Binds 1 zinc ion per subunit (PubMed:29540745). VAMP2 cleavage inhibited by EDTA. Apparent rate is 271 min(-1). Heterodimer; disulfide-linked heterodimer of a light chain (LC) and heavy chain (HC) (PubMed:28770820). Has protease activity. Has 3 functional domains; the translocation domain (TD) and the receptor-binding domain (RBD) which is further subdivided into N- and C-terminal domains (N-RBD and C-RBD). The N-terminus of the TD wraps an extended belt around the perimeter of the LC, protecting Zn(2+) in the active site and may be a pseudosubstrate inhibitor which serves as an intramolecular chaperone for the LC prior to its translocation into the host cytosol. The RBD binds transiently exposed coreceptors on the host presynaptic cell membrane. An interchain disulfide bond is required for toxin stability in an artificial construct with the light chain and translocation domain; which of Cys-461 or Cys-467 forms the disulfide bond with Cys-423 in vivo is unknown. The inactive construct (Ala-360--363-Tyr) can be used to generate antibodies against this serotype. Additionally the enlarged substrate specificity can be used to understand the function of VAMP4, VAMP5 and YKT6. There are seven antigenically distinct forms of botulinum neurotoxin: Types A, B, C, D, E, F, and G; new subtypes are quite frequent. This toxin is not recognized or neutralized by any of the antisera against the standard serotypes (PubMed:28770820). Botulism poisoning is usually food-borne, either by ingesting toxin or bacterial-contaminated food, or less frequently by inhalation poisoning. In both cases the neurotoxin binds to the apical surface of epithelial cells in the gut or airway. Toxin undergoes receptor-mediated endocytosis (using a different receptor than on target nerve cells), transcytosis across the epithelial cells and release into the general circulation. Once in the general circulation it binds to its target cells. This strain was isolated from an infant botulism patient in Japan in 1996; toxicity of this strain is due to a type B neurotoxin (PubMed:8942019). This locus has includes a number of other genes usually associated with the botulinum neurotoxin cluster in Clostridia (p47, hemagglutinin genes and the OrfX cluster), which should permit the toxin to survive in a host. It remains unknown whether BoNT/X is ever produced in C.botulinum strain 111. Belongs to the peptidase M27 family.