Protein: Botulinum neurotoxin type A (BoNT/A) (Bontoxilysin-A) (BOTOX) (Botulinum neurotoxin type A1) [Cleaved into: Botulinum neurotoxin A light chain (LC) (EC 3.4.24.69); Botulinum neurotoxin A heavy chain (HC)] (P0DPI0)
Organism: Clostridium botulinum
Function: Botulinum toxin causes flaccid paralysis by inhibiting neurotransmitter (acetylcholine) release from the presynaptic membranes of nerve terminals of the eukaryotic host skeletal and autonomic nervous system, with frequent heart or respiratory failure. Precursor of botulinum neurotoxin A which has 2 coreceptors; complex polysialylated gangliosides found on neural tissue and specific membrane-anchored proteins of 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 the 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. Toxin activity requires polysialylated gangliosides; GT1b supports activity better than GD1a. Binds to host peripheral neuronal presynaptic membranes via the synaptic vesicle glycoproteins SV2A, SV2B and SV2C. It binds directly to the largest lumenal (intravesicular) loop of SV2A, SV2B and SV2C that is transiently exposed outside of cells during exocytosis; gangliosides enhance binding. Recognizes an N-linked glycan on SV2 proteins. May also use FGFR3 as a receptor. Toxin uptake into neural cells requires stimulation (incubation with K(+) to stimulate receptor exposure) to be internalized by receptor-mediated endocytosis. Subsequently the toxin colocalizes with its receptor in host cells. Toxin uptake can be blocked by the appropriate SV2 protein fragments in cell culture.
Subcellular location: [Botulinum neurotoxin type A]: Secreted {ECO:0000269|PubMed:7592120}. Secreted, cell wall {ECO:0000269|PubMed:7592120}. Host synapse, host presynaptic cell membrane {ECO:0000269|PubMed:6694738}. Note=Whole toxin may be released from the bacteria during cell wall exfoliation (PubMed:7592120). There are estimated to be 150-500 toxin molecules per um(2) of non-myelinated mouse hemidiaphragm nerve membrane (PubMed:6694738). In mouse hemidiaphragm binds only to nerve terminals, and not to muscle, blood vessels, connective tissue Schwann cells or myelin, toxin can be internalized by this preparation (PubMed:6694738). {ECO:0000269|PubMed:6694738, ECO:0000269|PubMed:7592120}.; SUBCELLULAR LOCATION: [Botulinum neurotoxin A light chain]: Secreted {ECO:0000269|PubMed:6370252}. Host cytoplasm, host cytosol {ECO:0000305|PubMed:7578132, ECO:0000305|PubMed:8243676, ECO:0000305|PubMed:9886085}.; SUBCELLULAR LOCATION: [Botulinum neurotoxin A heavy chain]: Secreted {ECO:0000269|PubMed:6370252}. Host synapse, host presynaptic cell membrane {ECO:0000269|PubMed:6694738, ECO:0000305|PubMed:10413679}. Host cytoplasmic vesicle, host secretory vesicle, host synaptic vesicle membrane {ECO:0000269|PubMed:23471747, ECO:0000305|PubMed:10413679, ECO:0000305|PubMed:21632541, ECO:0000305|PubMed:21832053, ECO:0000305|PubMed:24240280, ECO:0000305|PubMed:6694738}; Multi-pass membrane protein {ECO:0000305|PubMed:17666397, ECO:0000305|PubMed:19096517, ECO:0000305|PubMed:2446925}. Note=Whole toxin may be released from the bacteria during cell wall exfoliation (PubMed:7592120). Colocalizes with its receptor SV2C (synaptic vesicle glycoprotein 2C) and VGAT (vesicular inhibitory amino acid transporter) in neurons (PubMed:24240280). In neurons HC colocalizes with synaptophysin or VAMP2 probably in synaptic vesicles, a portion also colocalizes with RAB5 and may be in synaptic vesicle protein sorting endosomes (PubMed:21632541, PubMed:21832053). Therefore there may be more than one uptake pathway at nerve terminals. Uptake of HC and whole toxin is slowed by dynamin inhibitors (PubMed:21832053). 1-2 molecules of HC are found in the host synaptic vesicle lumen, uptake and subsequent release of LC is very rapid (PubMed:21832053, PubMed:23471747). {ECO:0000269|PubMed:21632541, ECO:0000269|PubMed:21832053, ECO:0000269|PubMed:23471747, ECO:0000269|PubMed:24240280}.
Interaction partners:
Sequence:
MPFVNKQFNYKDPVNGVDIAYIKIPNVGQMQPVKAFKIHNKIWVIPERDTFTNPEEGDLNPPPEAKQVPVSYYDSTYLSTDNEKDNYLKGVTKLFERIYSTDLGRMLLTSIVRGIPFWGGSTIDTELKVIDTNCINVIQPDGSYRSEELNLVIIGPSADIIQFECKSFGHEVLNLTRNGYGSTQYIRFSPDFTFGFEESLEVDTNPLLGAGKFATDPAVTLAHELIHAGHRLYGIAINPNRVFKVNTNAYYEMSGLEVSFEELRTFGGHDAKFIDSLQENEFRLYYYNKFKDIASTLNKAKSIVGTTASLQYMKNVFKEKYLLSEDTSGKFSVDKLKFDKLYKMLTEIYTEDNFVKFFKVLNRKTYLNFDKAVFKINIVPKVNYTIYDGFNLRNTNLAANFNGQNTEINNMNFTKLKNFTGLFEFYKLLCVRGIITSKTKSLDKGYNKALNDLCIKVNNWDLFFSPSEDNFTNDLNKGEEITSDTNIEAAEENISLDLIQQYYLTFNFDNEPENISIENLSSDIIGQLELMPNIERFPNGKKYELDKYTMFHYLRAQEFEHGKSRIALTNSVNEALLNPSRVYTFFSSDYVKKVNKATEAAMFLGWVEQLVYDFTDETSEVSTTDKIADITIIIPYIGPALNIGNMLYKDDFVGALIFSGAVILLEFIPEIAIPVLGTFALVSYIANKVLTVQTIDNALSKRNEKWDEVYKYIVTNWLAKVNTQIDLIRKKMKEALENQAEATKAIINYQYNQYTEEEKNNINFNIDDLSSKLNESINKAMININKFLNQCSVSYLMNSMIPYGVKRLEDFDASLKDALLKYIYDNRGTLIGQVDRLKDKVNNTLSTDIPFQLSKYVDNQRLLSTFTEYIKNIINTSILNLRYESNHLIDLSRYASKINIGSKVNFDPIDKNQIQLFNLESSKIEVILKNAIVYNSMYENFSTSFWIRIPKYFNSISLNNEYTIINCMENNSGWKVSLNYGEIIWTLQDTQEIKQRVVFKYSQMINISDYINRWIFVTITNNRLNNSKIYINGRLIDQKPISNLGNIHASNNIMFKLDGCRDTHRYIWIKYFNLFDKELNEKEIKDLYDNQSNSGILKDFWGDYLQYDKPYYMLNLYDPNKYVDVNNVGIRGYMYLKGPRGSVMTTNIYLNSSLYRGTKFIIKKYASGNKDNIVRNNDRVYINVVVKNKEYRLATNASQAGVEKILSALEIPDVGNLSQVVVMKSKNDQGITNKCKMNLQDNNGNDIGFIGFHQFNNIAKLVASNWYNRQIERSSRTLGCSWEFIPVDDGWGERPL