Fig. 5
From: Elucidating the activation mechanism of botulinum neurotoxin a: role of α-clostripain and NTNH
Protection of BoNT/A by NTNH facilitates specific cleavage for toxin activation. NTNH shields the receptor-binding domain of the toxin while leaving the activation loop, which connects the toxin LC and HC, available for cleavage by proteases. The model was prepared by superposition of a predicted BoNT/A structure (Alphafold code AF-P0DPI1-F1-v4 (Jumper, Evans et al., 2021)) and the BoNT/Ai chain from the crystal structure of the BoNT/A-NTNH complex (PDB code 3v0a (Gu, Rumpel et al., 2012)). NTNH is colored beige and shown in surface display. BoNT/A is in cartoon representation and is colored according to Alphafold’s per-residue model confidence score. Confidence levels are represented by a spectrum from blue to red, with blue representing highly confident regions, transitioning to yellow (medium confidence), and red (low confidence). Cys430 and Cys454, which connect the toxin LC and HC, are in stick representation and colored yellow. Arginine (magenta) and lysine (green) residues on the activation loop, which represent potential α-clostripain cleavage sites, are also shown in stick representation.
