Clostridium botulinum neurotoxin (BoNT) type E (The 3d structure is known (Kumaran et al., 2009)). BoNT consists of a light chain (L) and a heavy chain (H) linked by a disulfide bond, where the heavy chain is divided into a translocation domain and an acceptor binding domain (Hc). Tan et al. 2023 explored a recombinant L-HN fragment (EL-HN) composed of the L and HN domains of BoNT/E. Neurotoxicity of L-HN fragments was assessed in mice, and the receptor synaptic vesicle glycoprotein 2C (SV2C) was explored. The 50% mouse lethal dose of the nicked dichain EL-HN fragment (EL-HN-DC) was 0.5 mug, and its neurotoxicity was the highest among the L-HN's of the four serotypes of BoNT(A/B/E/F). The cleavage efficiency of EL-HN-DC toward synaptosome- associated protein 25 (SNAP25) in vitro was 3-fold higher than that of the single chain at the cellular level, and showed 200-fold higher animal toxicity. The EL-HN-DC fragment might enter  cells via binding to SV2C to efficiently cleave SNAP25. Thus, the EL-HN fragment showed good biological activity and could be used as a drug screening model and to further explore the molecular mechanism of its transmembrane transport (Tan et al. 2023).