Molecular Mechanism of Action for Particularly Potent Marine Biotoxins.

美托毒素（MTX）最初被发现是造成雪卡毒的毒素之一，雪卡毒是一种因食用珊瑚礁鱼类而引起的海鲜中毒。MTX具有极强的生物活性，其毒性尤其值得注意，LD_<50>（50 ng/kg，小鼠ip.）只有几种蛋白质毒素超过它MTX在几乎所有的细胞和组织中都能增加Ca^2+内流，这种细胞内钙浓度的升高会导致继发性事件，例如，磷酸肌醇分解，花生四烯酸释放，肌肉收缩，以及多巴胺、去甲肾上腺素和胰岛素的分泌。神经节苷脂GM 1和GM 3可明显抑制MTX诱导的C6细胞内Ca^2+内流。它们的抑制效力为GM_1（IC_<50>，ca. 2 μM）&gt; GM 3（约. 5 μM）&gt;去唾液酸-GM 1（约. 20 μM）。在人红细胞血影中，GM 1（3 μM）完全阻断MTX（30 nM）诱导的Ca^2+内流。当C6细胞用衣霉素（一种抑制N-连接糖基化的抗生素）或伴刀豆球蛋白A（一种对细胞表面寡糖具有高亲和力的凝集素）预处理时，MTX诱导的Ca^2+内流显著增强。这表明，从细胞表面的衣霉素或帽的质膜上的糖链上的刀豆球蛋白A的寡糖的去除可以增强MTX的作用。光亲和标记实验，以确定MTX结合蛋白进行了使用daizirine-biotin共轭试剂开发的Hatanaka。通过加入MTX抑制剂短毒素-B，消除了2D电泳上的一些斑点，对应于2KDa。

Maitotoxin (MTX) was first discovered as one of the toxins responsible for ciguatera, a seafood poisoning caused by ingestion of coral reef fish. MTX has extremely potent bioactivities ; its toxicity is particularly worth noting, since its LD_<50>(50 ng/kg, mouse ip.) is exceeded only by a few proteinaceous toxins. MTX elicits Ca^<2+> influx in virtually all cells and tissues and this elevation in intracellular calcium concentration leads to secondary events ; e.g., phosphoinositide breakdown, arachidonic acid release, muscle contraction, and secretion of dopamine, norepinephrine, and insulin. Gangliosides GM1 and GM3 strongly inhibited MTX-induced Ca^<2+> influx in C6 cells. Their inhibitory potency was in the order GM1 (IC_<50>, ca. 2 μM)>GM3 (ca. 5 μM)>asialo-GM1 (ca. 20 μM). GM1 (3 μM) completely blocked MTX(30 nM)-induced Ca^<2+> influx in human erythrocyte ghosts. When C6 cells were pretreated with tunicamycin, an antibiotic which inhibits N-linked glycosylation, or concanavalin A, a lectin which exhibits high affinity for cell-surface oligosaccharides, MTX-induced Ca^<2+> influx was significantly potentiated. This suggests that removal of oligosaccharides from the cell surface by tunicamycin or capping of sugar chains on plasma membranes by concanavalin A can potentiate the action of MTX.Photoaffinity labeling experiment to identify MTX-binding protein was carried out with use of a daizirine-biotin conjugated reagent developed by Hatanaka. Some spots on 2D electrophoresis, corresponding to 2 KDa were eliminated by addition of an MTX inhibitor, brevetoxin-B.