Botulinum neurotoxin type D - P19321 (BXD_CLOBO)

 

Protein Feature View of PDB entries mapped to a UniProtKB sequence  

  • Number of PDB entries for P19321: 9
 
Function
Botulinum neurotoxin type D: 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 (PubMed:8175689, PubMed:16252491). Precursor of botulinum neurotoxin D for which a proteinaceous coreceptor is controversial. In double SV2A/SV2B knockout mice this toxin does not degrade its synaptobrevin target; introducing SV2A, SV2B or SV2C restores target cleavage (PubMed:21483489). Recognition of SV2 by this toxin does not occur via SV2 glycosylation or its large extracellular loop 4 (PubMed:21483489). Another group does not find a convincing interaction with SV2 (PubMed:21632541). Thus a protein receptor for this BoNT serotype has yet to be definitively proven. Recognizes at least 1 complex polysialylated ganglioside found on neural tissue. Electrical stimulation increases uptake of toxin in an ex vivo assay, presumably by transiently exposing a receptor usually found in eukaryotic target synaptic vesicles (PubMed:19650874, PubMed:21483489, PubMed:21632541). 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 heavy chain (HC) forms pores that allows the light chain (LC) to translocate into the cytosol (By similarity). 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). Requires complex eukaryotic host polysialogangliosides for full neurotoxicity and for binding to neurons (PubMed:20704566, PubMed:21483489). UniProt
Catalytic Activity
Limited hydrolysis of proteins of the neuroexocytosis apparatus, synaptobrevins, SNAP25 or syntaxin. No detected action on small molecule substrates. UniProt
Pathway Maps
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Subunit Structure
Heterodimer; disulfide-linked heterodimer of a light chain (LC) and a heavy chain (HC) (PubMed:26324071). The LC has the proteolytic/pharmacological activity (PubMed:8175689, PubMed:8197120). The N- and C-termini of the HC mediate channel formation and eukaryotic host cell binding, respectively. Can also be purified in complex with a non-toxic component that is larger than the HC (PubMed:16252491). HC interacts with eukaryotic protein synaptic vesicle glycoprotein 2B (SV2B), which may serve as its receptor (PubMed:21483489). Another group does not find a convincing interaction with SV2 (PubMed:21632541). UniProt
Domain
Botulinum neurotoxin D heavy chain: 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, also called Hcn and Hcc) (PubMed:20731382, PubMed:20704566). The N-terminus of the TD wraps an extended belt around the perimeter of the LC which occludes the catalytic pocket (PubMed:26324071). The belt region may be a pseudosubstrate inhibitor which serves as an intramolecular chaperone for the LC prior to its translocation into the host cytosol (PubMed:17907800). UniProt
  • Other Gene names: botD
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