Department of Physiology and Biophysics, University of California, Irvine, California, United States of America.
PLoS Pathog. 2013;9(10):e1003690. doi: 10.1371/journal.ppat.1003690. Epub 2013 Oct 10.
Botulinum neurotoxins (BoNTs) are produced by Clostridium botulinum and cause the fatal disease botulism, a flaccid paralysis of the muscle. BoNTs are released together with several auxiliary proteins as progenitor toxin complexes (PTCs) to become highly potent oral poisons. Here, we report the structure of a ∼760 kDa 14-subunit large PTC of serotype A (L-PTC/A) and reveal insight into its absorption mechanism. Using a combination of X-ray crystallography, electron microscopy, and functional studies, we found that L-PTC/A consists of two structurally and functionally independent sub-complexes. A hetero-dimeric 290 kDa complex protects BoNT, while a hetero-dodecameric 470 kDa complex facilitates its absorption in the harsh environment of the gastrointestinal tract. BoNT absorption is mediated by nine glycan-binding sites on the dodecameric sub-complex that forms multivalent interactions with carbohydrate receptors on intestinal epithelial cells. We identified monosaccharides that blocked oral BoNT intoxication in mice, which suggests a new strategy for the development of preventive countermeasures for BoNTs based on carbohydrate receptor mimicry.
肉毒杆菌神经毒素（BoNTs）由肉毒梭菌产生，可导致致命疾病肉毒中毒，即肌肉弛缓性瘫痪。BoNTs 与几种辅助蛋白一起作为原毒素复合物（PTC）释放，成为高毒口服毒物。在此，我们报告了血清型 A（L-PTC/A）的约 760 kDa 14 亚基大 PTC 的结构，并揭示了其吸收机制的见解。我们使用 X 射线晶体学、电子显微镜和功能研究的组合，发现 L-PTC/A 由两个结构和功能上独立的亚复合物组成。一个异二聚体 290 kDa 复合物保护 BoNT，而一个异十二聚体 470 kDa 复合物在胃肠道恶劣的环境中促进其吸收。BoNT 的吸收是由十二聚体亚复合物上的九个糖结合位点介导的，该亚复合物与肠上皮细胞上的碳水化合物受体形成多价相互作用。我们鉴定出了可阻断小鼠口服 BoNT 中毒的单糖，这表明了基于碳水化合物受体模拟的 BoNT 预防性对策的新策略。
