Botulinum neurotoxin (BoNT) is the causative agent of botulism in humans and animals. Only BoNT serotype A subtype 1 (BoNT/A1) is used clinically because of its high potency and long duration of action. BoNT/A1 and BoNT/A subtype 2 (BoNT/A2) have a high degree of amino acid sequence similarity in the light chain (LC) (96%), whereas their N‐and C‐terminal heavy chain (H_N and H_C) differ by 13%. The LC acts as a zinc‐dependent endopeptidase, H_N as the translocation domain, and H_C as the receptor‐binding domain. BoNT/A2 and BoNT/A1 had similar potency in the mouse bioassay, but BoNT/A2 entered faster and more efficiently into neuronal cells. To identify the domains responsible for these characteristics, H_N of BoNT/A1 and BoNT/A2 was exchanged to construct chimeric BoNT/A121 and BoNT/A212. After expression in Escherichia coli , chimeric and wild‐type BoNT/As were purified as single‐chain proteins and activated by conversion to disulfide‐linked dichains. The toxicities of recombinant wild‐type and chimeric BoNT/As were similar, but dropped to 60% compared with the values of native BoNT/As. The relative orders of SNAP‐25 cleavage activity in neuronal cells and toxicity differed. BoNT/A121 and recombinant BoNT/A2 have similar SNAP‐25 cleavage activity. BoNT/A2 H_N is possibly responsible for the higher potency of BoNT/A2 than BoNT/A1.

中文翻译：

---

肉毒杆菌神经毒素A亚型2的易位域有效诱导进入神经元细胞。

肉毒杆菌神经毒素（BoNT）是人类和动物中肉毒杆菌中毒的病原。临床上仅使用BoNT血清型A亚型1（BoNT / A1），因为其效力高且作用时间长。BoNT / A1和BoNT / A 2型（BoNT / A2）在轻链（LC）（96％）中具有高度的氨基酸序列相似性，而它们的N端和C端重链（H _N和H _C）相差13％。LC充当锌依赖性肽链内切酶，H _N充当易位域，H _C充当受体结合域。BoNT / A2和BoNT / A1在小鼠生物测定中的效价相似，但BoNT / A2可以更快，更有效地进入神经元细胞。为了确定负责这些特征的域，H _N将BoNT / A1和BoNT / A2的一部分交换以构建嵌合的BoNT / A121和BoNT / A212。在大肠杆菌中表达后，嵌合和野生型BoNT / As被纯化为单链蛋白，并通过转化为二硫键连接的双链而被激活。重组野生型和嵌合BoNT / As的毒性相似，但与天然BoNT / As相比降低到60％。SNAP-25裂解活性在神经元细胞和毒性的相对顺序有所不同。BoNT / A121和重组BoNT / A2具有相似的SNAP-25裂解活性。BoNT / A2 H _N可能是BoNT / A2比BoNT / A1具有更高效力的原因。