C. botulinum BoNT‑C1 Heavy Chain Antibody

BoNT-C1 (Botulinum neurotoxin C1 [heavy chain]) is a 100 kDa C-terminal fragment of the C1 Clostridum botulinum neurotoxin (holo)precursor. It constitutes a nonenzymatic part of a Zn²⁺-dependent M27 family endoprotease that potently blocks neurosecretion. The inactive 1291 amino acid (aa), 150 kDa C1 precursor is cleaved between Lys449Thr450 to generate a heterodimeric toxin held together by a preexisting interchain disulfide bond between Cys437 and Cys453. The 100 kDa C-terminus (heavy chain) acts as a ligand for neuronal membrane ecto-acceptors, inducing its translocation and internalization. The 50 kDa N-terminal light chain acts as an intracellular peptidase that cleaves SNAP-25 and syntaxin. This is suggested to block noradrenalin release from a readily releasable pool of vesicles. Over aa 866-1291, the C1 heavy chain shares less than 40% aa identity with the D-type neurotoxin heavy chain.