Morris R E, Gerstein A S, Bonventre P F, Saelinger C B
Infect Immun. 1985 Dec;50(3):721-7. doi: 10.1128/iai.50.3.721-727.1985.
To express toxicity in living cells, diphtheria toxin (DT) must cross a membrane barrier and reach its target in the cytosol. Here we examine the entry of DT into the toxin-sensitive monkey kidney (Vero) cells. Using electron microscopy we directly demonstrated for the first time that DT is internalized by receptor-mediated endocytosis, i.e., via clathrin-coated pits, and enters the endosomal system. Methylamine, which is known to protect cells from DT, stopped the movement of toxin to coated areas of the cell membrane. In the presence of amine, prebound biotinyl-DT was internalized, but toxicity was inhibited. Biochemical evidence revealed that methylamine maintained toxin molecules at a site accessible to neutralization by antitoxin. The data suggest that DT entering Vero cells in the presence of methylamine is sequestered within the cell and does not express toxicity.
为了在活细胞中表现出毒性，白喉毒素（DT）必须穿过膜屏障并到达其在细胞质中的靶点。在这里，我们研究了DT进入毒素敏感的猴肾（Vero）细胞的过程。通过电子显微镜，我们首次直接证明DT是通过受体介导的内吞作用内化的，即通过网格蛋白包被的小窝，并进入内体系统。已知能保护细胞免受DT侵害的甲胺，阻止了毒素向细胞膜包被区域的移动。在胺存在的情况下，预先结合的生物素化DT被内化，但毒性受到抑制。生化证据表明，甲胺将毒素分子维持在可被抗毒素中和的位置。数据表明，在甲胺存在的情况下进入Vero细胞的DT被隔离在细胞内，不表现出毒性。
