Marnell M H, Shia S P, Stookey M, Draper R K
Infect Immun. 1984 Apr;44(1):145-50. doi: 10.1128/iai.44.1.145-150.1984.
To kill mammalian cells, diphtheria toxin must be endocytosed and encounter a low pH within intracellular vesicles. The low pH initiates penetration of the catalytically active A fragment of the toxin through a membrane and into the cytosol where the A fragment arrests protein synthesis. To investigate whether penetration occurred through a prelysosomal or a lysosomal membrane, we studied the effect of low temperature on the entry of the toxin into the cytosolic and lysosomal compartments. The toxin arrested protein synthesis at 15 degrees C, indicating entry into the cytosol; however, access to lysosomes was apparently blocked at 15 degrees C, suggesting that the toxin had encountered a low pH before reaching lysosomes and had penetrated a prelysosomal membrane. To further investigate the possibility of prelysosomal acidification, we measured the time required for the toxin to encounter a low pH after endocytosis. Acidification occurred within 3 to 4 min after the toxin was internalized into vesicles. This interval is consistent with prelysosomal acidification since the entry of endocytosed ligands into secondary lysosomes usually takes more than 3 to 4 min.
要杀死哺乳动物细胞，白喉毒素必须被内吞，并在细胞内囊泡中遇到低pH值。低pH值引发毒素的催化活性A片段穿过膜进入胞质溶胶，在那里A片段会阻止蛋白质合成。为了研究穿透是通过前溶酶体膜还是溶酶体膜发生的，我们研究了低温对毒素进入胞质溶胶和溶酶体区室的影响。毒素在15℃时阻止了蛋白质合成，表明其进入了胞质溶胶；然而，在15℃时，毒素显然无法进入溶酶体，这表明毒素在到达溶酶体之前就遇到了低pH值，并穿透了前溶酶体膜。为了进一步研究前溶酶体酸化的可能性，我们测量了毒素内吞后遇到低pH值所需的时间。毒素被内化到囊泡后3至4分钟内发生了酸化。这个时间间隔与前溶酶体酸化一致，因为内吞的配体进入次级溶酶体通常需要超过3至4分钟。
