Laboratory of Protein Dynamics and Signaling, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702;
Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218.
Proc Natl Acad Sci U S A. 2017 Jun 27;114(26):E5158-E5166. doi: 10.1073/pnas.1621076114. Epub 2017 Jun 5.
Botulism is characterized by flaccid paralysis, which can be caused by intoxication with any of the seven known serotypes of botulinum neurotoxin (BoNT), all of which disrupt synaptic transmission by endoproteolytic cleavage of SNARE proteins. BoNT serotype A (BoNT/A) has the most prolonged or persistent effects, which can last several months, and exerts its effects by specifically cleaving and inactivating SNAP25. A major factor contributing to the persistence of intoxication is the long half-life of the catalytic light chain, which remains enzymatically active months after entry into cells. Here we report that BoNT/A catalytic light chain binds to, and is a substrate for, the ubiquitin ligase HECTD2. However, the light chain evades proteasomal degradation by the dominant effect of a deubiquitinating enzyme, VCIP135/VCPIP1. This deubiquitinating enzyme binds BoNT/A light chain directly, with the two associating in cells through the C-terminal 77 amino acids of the light chain protease. The development of specific DUB inhibitors, together with inhibitors of BoNT/A proteolytic activity, may be useful for reducing the morbidity and public health costs associated with BoNT/A intoxication and could have potential biodefense implications.
肉毒中毒的特征是弛缓性瘫痪，它可能是由任何七种已知类型的肉毒神经毒素（BoNT）引起的中毒引起的，所有这些毒素都通过 SNARE 蛋白的内切蛋白酶切割来破坏突触传递。BoNT 血清型 A（BoNT/A）具有最长或持续时间最长的作用，可持续数月，通过特异性切割和失活 SNAP25 发挥作用。导致中毒持续存在的一个主要因素是催化轻链的长半衰期，它在进入细胞后数月仍保持酶活性。在这里，我们报告 BoNT/A 催化轻链与泛素连接酶 HECTD2 结合，并作为其底物。然而，轻链通过去泛素化酶 VCIP135/VCPIP1 的显性作用逃避蛋白酶体降解。这种去泛素化酶直接与 BoNT/A 轻链结合，通过轻链蛋白酶的 C 末端 77 个氨基酸在细胞中两者相关联。特异性 DUB 抑制剂的开发，以及 BoNT/A 蛋白水解活性的抑制剂，可能有助于降低与 BoNT/A 中毒相关的发病率和公共卫生成本，并且可能具有潜在的生物防御意义。
