Top: A Ribbons representation of Clostridium botulinum neurotoxin B (BoNT-B). Helices in blue represent 3-10 helices. The three functional domains are labeled. Zinc and the coordinating residues in the catalytic domain are shown in ball and stick representation. Left: A Ribbons representation of of the BoNT-B ganglioside binding domain inlayed in its van der Waals surface. The sialyllactose (red) and the interacting residues (blue) are shown as solid van der Waals surfaces, while the rest of the surface is rendered transparent.

from: Swaminathan, S., and Eswaramoorthy, S., Structural analysis of the catalytic and binding sites of Clostridium botulinum neurotoxin B Nature Struct. Biol. 7, 693-699 (2000).  Medline Abstract;  PDB files 1EPW, 1F31