Fig. 1.

(A) Top view of a cantilever with a syntaxin 1A-functionalized tip above a synaptobrevin 2-functionalized bead. (B) Recombinant synaptobrevin 2 (red) is attached to the nickel-coated bead surface through a histidine residue tag at its C terminus, leaving its N terminus free to interact with the N terminus of recombinant syntaxin 1A, which is similarly attached by means of a C-terminal histidine tag to the nickel-coated cantilever tip. The synaptobrevin 2-syntaxin intermolecular interaction leads to the bead's being tethered to the cantilever tip. BoNT-B in the presence of zinc ions (Zn²⁺) cleaves synaptobrevin 2 in such manner that the short fragment of synaptobrevin 2 remaining on the bead has no ability to interact with syntaxin 1A on the cantilever tip, leading to the detachment of the bead from the tip (double-headed vertical arrow). The drawing in B is not to scale.