de Paiva A, Ashton A C, Foran P, Schiavo G, Montecucco C, Dolly J O
Department of Biochemistry, Imperial College of Science, Technology, and Medicine, London, England.
J Neurochem. 1993 Dec;61(6):2338-41. doi: 10.1111/j.1471-4159.1993.tb07482.x.
Although botulinum neurotoxin (BoNT) types A and B and tetanus toxin (TeTx) are specific inhibitors of transmitter release whose light chains contain a zinc-binding motif characteristic of metalloendoproteases, only the latter two proteolyse synaptobrevin. Chelation of zinc or its readdition at high concentration hindered blockade of neuromuscular transmission by BoNT/A and B, indicating that type A also acts via a zinc-dependent mechanism. Such treatments prevented proteolysis of synaptobrevin II in rat brain synaptic vesicles by BoNT/B and TeTx but only the activity of the latter was antagonised appreciably by ASQFETS, a peptide spanning their cleavage site. The toxin's neuroparalytic activities were attenuated by phosphoramidon or captopril, inhibitors of certain zinc requiring proteases. However, these agents were ineffective in reducing the toxins' degradation of synaptobrevin except that a high concentration of captopril partially blocked the activity of TeTx but not BoNT/B, as also found for these drugs when tested on synaptosomal noradrenaline release. These various criteria establish that a zinc-dependent protease activity underlies the neurotoxicity of BoNT/A, a finding confirmed at motor nerve endings for type B and TeTx. Moreover, the low potencies of captopril and phosphoramidon in counteracting the toxins' effects necessitate the design of improved inhibitors for possible use in the clinical treatment of tetanus or botulism.
虽然A型和B型肉毒杆菌神经毒素（BoNT）以及破伤风毒素（TeTx）是递质释放的特异性抑制剂，其轻链含有金属内蛋白酶特有的锌结合基序，但只有后两种毒素能蛋白水解突触小泡蛋白。锌螯合或高浓度重新添加锌会阻碍BoNT/A和B对神经肌肉传递的阻断，这表明A型毒素也通过锌依赖性机制起作用。此类处理可防止BoNT/B和TeTx对大鼠脑突触小泡中突触小泡蛋白II的蛋白水解作用，但只有TeTx的活性会被跨越其切割位点的肽ASQFETS明显拮抗。毒素的神经麻痹活性会被磷酰胺或卡托普利减弱，这两种物质是某些需锌蛋白酶的抑制剂。然而，这些药物在减少毒素对突触小泡蛋白的降解方面无效，只是高浓度的卡托普利部分阻断了TeTx的活性，但对BoNT/B无效，在测试这些药物对突触体去甲肾上腺素释放的作用时也有同样的发现。这些不同的标准表明，锌依赖性蛋白酶活性是BoNT/A神经毒性的基础，这一发现已在运动神经末梢对B型毒素和TeTx得到证实。此外，卡托普利和磷酰胺在对抗毒素作用方面效力较低，因此需要设计出改进的抑制剂，以便可能用于破伤风或肉毒中毒的临床治疗。
