Chen F, Kuziemko G M, Stevens R C
Graduate Group in Biophysics, University of California, Berkeley, CA 94720, USA.
Infect Immun. 1998 Jun;66(6):2420-5. doi: 10.1128/IAI.66.6.2420-2425.1998.
Botulinum neurotoxin serotype A is initially released from the bacterium Clostridium botulinum as a stable 900-kDa complex. The serotype A 900-kDa complex is one of the forms of the toxin being used as a therapeutic agent for the treatment of various neuromuscular disorders. Previous experiments have demonstrated that the 900-kDa complex form of the toxin protects the toxin from the harsh conditions of the gastrointestinal tract. To provide molecular level details of the stability and equilibrium of the 900-kDa complex, the nontoxic component, and the toxic (botulinum neurotoxin) component, the three species have been investigated with a series of biophysical techniques at the molecular level (dynamic light scattering, proteolysis, circular dichroism, pH incubations, and agglutination assays). These experiments were conducted under harsh conditions which mimic those found along the gastrointestinal tract. Separately, exposure to denaturing and proteolytic conditions degrades both the botulinum neurotoxin and the nontoxic component. In the 900-kDa complex, the botulinum neurotoxin is protected during exposure to the gastrointestinal environment and the nontoxic component is slightly modified. Surprisingly, the toxin protects the ability of the nontoxic component to agglutinate erythrocytes. Contrary to previous reports, the purified 900-kDa complex did not have agglutination ability until after exposure to the proteolytic conditions. These experiments provide new evidence and detail for the theory that the nontoxic component and the toxic component protect one another during exposure to harsh conditions, and a molecular model is presented for the passage of the toxin through the gastrointestinal tract.
A型肉毒杆菌神经毒素最初以稳定的900 kDa复合物形式从肉毒杆菌中释放出来。A型900 kDa复合物是该毒素用作治疗各种神经肌肉疾病的治疗剂的形式之一。先前的实验表明，毒素的900 kDa复合物形式可保护毒素免受胃肠道恶劣环境的影响。为了提供900 kDa复合物、无毒成分和有毒（肉毒杆菌神经毒素）成分的稳定性和平衡的分子水平细节，已在分子水平上用一系列生物物理技术（动态光散射、蛋白水解、圆二色性、pH孵育和凝集试验）对这三种物质进行了研究。这些实验是在模拟胃肠道环境的恶劣条件下进行的。另外，暴露于变性和蛋白水解条件下会使肉毒杆菌神经毒素和无毒成分都降解。在900 kDa复合物中，肉毒杆菌神经毒素在暴露于胃肠道环境时受到保护，无毒成分略有改变。令人惊讶的是，毒素保护无毒成分凝集红细胞的能力。与先前的报道相反，纯化的900 kDa复合物在暴露于蛋白水解条件之前没有凝集能力。这些实验为无毒成分和有毒成分在暴露于恶劣条件下相互保护的理论提供了新的证据和细节，并提出了毒素通过胃肠道的分子模型。
