Botulinum neurotoxicity

Authored: Krupa, S, Gopinathrao, G, 2006-06-15 10:36:11 Botulism, caused by botulinum neurotoxin (BoNT), is characterized by descending flaccid paralysis as a result of inhibition of neurotransmitter release at the neuromuscular junction - NMJ (Turton et al., 2002). According to their antigenic properties, BoNTs are classified into seven different toxin types (A, B, C1, D, E, F and G) although more than 50 sequences encoding 18 subtypes are known (Smith et al., 2005). The toxin is released as a 900 kDa complex containing some accessory proteins of unknown functions (Chen et al., 1998). The toxin types A, B and E are mainly involved in human botulism whereas C and D predominantly cause animal botulism (Poulain et al, 2006). The toxin is absorbed from the gut or other epithelium and reaches neuromuscular junctions by transcytosis (Park and Simpson, 2003). The binding sites for the toxins are distributed across the apical surface of the epithelium (Ahsan et al., 2005). It has been observed that the neurotoxin alone is capable of transcytosis across epithelial cells (Maksymowych and Simpson, 2004). Once internalized, the neurotoxin is dissociated from the non-toxic components of the progenitor toxin in endosome (Uotsu et al., 2006). <br> The neurological inhibition is caused by the specific cleavage of a group of proteins integral to NMJ exocytosis, SNARE proteins (soluble NSF-attachment protein receptors). One or more SNARE proteins are cleaved by BoNT, blocking the release of synaptic vesicular contents like acetylcholine as in the case of motor neurons. <br>BoNTs are synthesized as polypeptides of 150 kDa that are cleaved into heavy and light chains linked by a single disulfide bond. Cleavage takes place within a surface-exposed loop at the N-terminal of the Heavy chain subunit. Both bacterial and host endopeptidases can catalyze BoNT cleavage into heavy and light chains, but bacterial enzymes are thought to carry out this function in vivo.The Heavy Chain (HC) has two 50 kDa functional domains: the N-terminal translocation domain is capable of forming channels in lipid bilayers; the C-terminal ganglioside-binding domain is important for membrane binding and subsequent internalization of toxins by host neurons. The 50 kDa Light chain (LC) is a zinc-dependent endopeptidase specific for core components of neurotransmitter release complexes.<br>BoNT action proceeds in the following steps: binding of cleaved toxin to the target cell membrane; transcytosis from epithelial membrane to target neuromuscular junction cells; release of BoNT Light chain into the target cell cytosol; and proteolytic cleavage of target cell proteins catalyzed by the BoNT Light chain.<br> Edited: Gopinathrao, G, 2006-06-15 22:12:29 Reviewed: Ichtchenko, K, 2007-08-03 18:17:25

http://purl.obolibrary.org/obo/HINO_0015696

Authored: Krupa, S, Gopinathrao, G, 2006-06-15 10:36:11

Botulism, caused by botulinum neurotoxin (BoNT), is characterized by descending flaccid paralysis as a result of inhibition of neurotransmitter release at the neuromuscular junction - NMJ (Turton et al., 2002). According to their antigenic properties, BoNTs are classified into seven different toxin types (A, B, C1, D, E, F and G) although more than 50 sequences encoding 18 subtypes are known (Smith et al., 2005). The toxin is released as a 900 kDa complex containing some accessory proteins of unknown functions (Chen et al., 1998). The toxin types A, B and E are mainly involved in human botulism whereas C and D predominantly cause animal botulism (Poulain et al, 2006). The toxin is absorbed from the gut or other epithelium and reaches neuromuscular junctions by transcytosis (Park and Simpson, 2003). The binding sites for the toxins are distributed across the apical surface of the epithelium (Ahsan et al., 2005). It has been observed that the neurotoxin alone is capable of transcytosis across epithelial cells (Maksymowych and Simpson, 2004). Once internalized, the neurotoxin is dissociated from the non-toxic components of the progenitor toxin in endosome (Uotsu et al., 2006).
The neurological inhibition is caused by the specific cleavage of a group of proteins integral to NMJ exocytosis, SNARE proteins (soluble NSF-attachment protein receptors). One or more SNARE proteins are cleaved by BoNT, blocking the release of synaptic vesicular contents like acetylcholine as in the case of motor neurons.
BoNTs are synthesized as polypeptides of 150 kDa that are cleaved into heavy and light chains linked by a single disulfide bond. Cleavage takes place within a surface-exposed loop at the N-terminal of the Heavy chain subunit. Both bacterial and host endopeptidases can catalyze BoNT cleavage into heavy and light chains, but bacterial enzymes are thought to carry out this function in vivo.The Heavy Chain (HC) has two 50 kDa functional domains: the N-terminal translocation domain is capable of forming channels in lipid bilayers; the C-terminal ganglioside-binding domain is important for membrane binding and subsequent internalization of toxins by host neurons. The 50 kDa Light chain (LC) is a zinc-dependent endopeptidase specific for core components of neurotransmitter release complexes.
BoNT action proceeds in the following steps: binding of cleaved toxin to the target cell membrane; transcytosis from epithelial membrane to target neuromuscular junction cells; release of BoNT Light chain into the target cell cytosol; and proteolytic cleavage of target cell proteins catalyzed by the BoNT Light chain.

Edited: Gopinathrao, G, 2006-06-15 22:12:29

Reviewed: Ichtchenko, K, 2007-08-03 18:17:25

Pubmed12417130

Pubmed15140915

Reactome, http://www.reactome.org

Pubmed9596697

Pubmed16144978

Pubmed16113261

Pubmed7527117

Pubmed12595426

Pubmed16413070

Botulinum neurotoxicity

http://purl.obolibrary.org/obo/NCBITaxon_9606

Neurotoxicity of Botulinum toxins

HINO:0015696

Botulinum neurotoxicity

ReactomeREACT_11184

GENE ONTOLOGYGO:0007269

Reactome Database ID Release 43168799

http://purl.obolibrary.org/obo/INO_0000021

http://purl.obolibrary.org/obo/HINO_0026836

http://purl.obolibrary.org/obo/HINO_0015701

http://purl.obolibrary.org/obo/HINO_0015702

http://purl.obolibrary.org/obo/HINO_0026740