A Comprehensive Structural Analysis of Clostridium botulinum Neurotoxin A Cell-Binding Domain from Different Subtypes

Abstract

Botulinum neurotoxins (BoNTs) cause flaccid neuromuscular paralysis by cleaving one of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex proteins. BoNTs display high affinity and specificity for neuromuscular junctions, making them one of the most potent neurotoxins known to date. There are seven serologically distinct BoNTs (serotypes BoNT/A to BoNT/G) which can be further divided into subtypes (e.g., BoNT/A1, BoNT/A2…) based on small changes in their amino acid sequence. Of these, BoNT/A1 and BoNT/B1 have been utilised to treat various diseases associated with spasticity and hypersecretion. There are potentially many more BoNT variants with differing toxicological profiles that may display other therapeutic benefits. This review is focused on the structural analysis of the cell-binding domain from BoNT/A1 to BoNT/A6 subtypes (HC/A1 to HC/A6), including features such as a ganglioside binding site (GBS), a dynamic loop, a synaptic vesicle glycoprotein 2 (SV2) binding site, a possible Lys–Cys/Cys–Cys bridge, and a hinge motion between the HCN and HCC subdomains. Characterising structural features across subtypes provides a better understanding of how the cell-binding domain functions and may aid the development of novel therapeutics.

Physical Treatments to Control Clostridium botulinum Hazards in Food

“…Neurotoxigenic Clostridium strains are also classified according to the type of toxin they produce. Currently, nine types of BoNTs have been identified: A, B, C, D, E, F, G, H, and X [ 26 ], but only the first seven (A to G) are considered for this classification [ 25 , 27 ]. Table 1 gives the correspondence between groups I to III, and the types of toxins produced [ 28 ].…”

“…Here, the heavy chain of activated toxin allows for endocytosis of the low chain into the peripheral neuron cell, which then binds to the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. These proteins are responsible for the exocytosis of acetylcholine synaptosomes, and they are destroyed by this toxin binding [ 20 , 27 ]. Consequently, the acetylcholine is not released and the nerve activity used to control the muscles is lost [ 36 ].…”

Crystal Structure of the Catalytic Domain of a Botulinum Neurotoxin Homologue from Enterococcus faecium: Potential Insights into Substrate Recognition

“…The domain organisation of the BoNT/En AlphaFold2-predicted structure appears to be ‘in between’ the two domain organisations determined experimentally. In the crystal structure of BoNT/A [ 7 ] and BoNT/B [ 21 ], the domain organisation is described as an ‘open-wing’ conformation [ 5 , 22 ] with all three domains in the same plane. In the BoNT/E structure, the H C domain and LC domain display a ‘closed-wing’ conformation [ 8 ].…”

“…Botulinum neurotoxins (BoNTs) are produced by the anaerobic spore-forming bacteria Clostridium botulinum and cause neuromuscular paralysis (i.e., botulism) by proteolytic cleavage of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins [ 1 ]. Eight serologically distinct BoNTs from Clostridium botulinum (BoNT/A-BoNT/G, and BoNT/X) have been identified [ 2 , 3 , 4 ] that vary in receptor [ 5 ] and substrate recognition [ 6 ]. All BoNTs are expressed as a single polypeptide chain that must be cleaved post-translationally to form the active di-chain molecule which is comprised of a 100 kDa heavy chain (HC) and 50 kDa light chain (LC).…”