Furutani M, Kashiwagi K, Ito K, Endo Y, Igarashi K
Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Arch Biochem Biophys. 1992 Feb 14;293(1):140-6. doi: 10.1016/0003-9861(92)90376-8.
The modes of action of a Vero toxin (VT2 or Shiga-like toxin II) from Escherichia coli, of ricin, and of alpha-sarcin were compared. Elongation factor 1 (EF1) and GTP-dependent Phe-tRNA binding to ribosomes in the presence of poly(U) was inhibited by these three toxins, but EF1 and guanylyl (beta, gamma-methylene)-diphosphate-dependent Phe-tRNA binding was inhibited by alpha-sarcin only. EF1- and Phe-tRNA-dependent GTPase activity was inhibited by these toxins, but nonenzymatic binding of Phe-tRNA was not. The turnover rate of EF1 binding to ribosomes during Phe-tRNA binding was also decreased by these three toxins. The addition of EF1 recovered the inhibition of Phe-tRNA binding to ribosomes by VT2 and ricin but not by alpha-sarcin. The formation of and EF2- and GTP-dependent puromycin derivative of phenylalanine was inhibited slightly by the three toxins, indicating that translocation is not influenced significantly by them. EF2-dependent GTPase activity was stimulated by these toxins, and especially by VT2 and ricin. In contrast, the binding of EF2 to ribosomes was inhibited strongly by VT2 and ricin, and slightly by alpha-sarcin. The stimulation of EF2-dependent GTPase activity by the toxins may compensate for the decrease of EF2 binding to ribosomes which they caused during translocation. In total, these results indicate that VT2 and ricin inhibit protein synthesis through the disturbance of the turnover of EF1 binding to ribosomes during aminoacyl-tRNA binding to ribosomes, and that alpha-sarcin inhibits the synthesis through the inhibition of the binding of the complex of Phe-tRNA, EF1, and GTP to ribosomes.
对来自大肠杆菌的Vero毒素（VT2或志贺样毒素II）、蓖麻毒素和α-肌动蛋白的作用模式进行了比较。在聚尿苷酸（poly(U)）存在的情况下，这三种毒素均抑制延伸因子1（EF1）和GTP依赖性苯丙氨酰-tRNA与核糖体的结合，但仅α-肌动蛋白抑制EF1和鸟苷酰（β，γ-亚甲基）-二磷酸依赖性苯丙氨酰-tRNA的结合。这些毒素抑制EF1和苯丙氨酰-tRNA依赖性GTP酶活性，但不抑制苯丙氨酰-tRNA的非酶促结合。在苯丙氨酰-tRNA结合过程中，EF1与核糖体结合的周转速率也被这三种毒素降低。添加EF1可恢复VT2和蓖麻毒素对苯丙氨酰-tRNA与核糖体结合的抑制作用，但不能恢复α-肌动蛋白的抑制作用。这三种毒素轻微抑制了苯丙氨酸的EF2和GTP依赖性嘌呤霉素衍生物的形成，表明转位不受它们的显著影响。这些毒素刺激EF2依赖性GTP酶活性，尤其是VT2和蓖麻毒素。相反，VT2和蓖麻毒素强烈抑制EF2与核糖体的结合，α-肌动蛋白则轻微抑制。毒素对EF2依赖性GTP酶活性的刺激可能补偿了它们在转位过程中导致的EF2与核糖体结合的减少。总的来说，这些结果表明，VT2和蓖麻毒素通过在氨酰-tRNA与核糖体结合过程中干扰EF1与核糖体结合的周转来抑制蛋白质合成，而α-肌动蛋白通过抑制苯丙氨酰-tRNA、EF1和GTP复合物与核糖体的结合来抑制合成。
