Perera L P, Samuel J E, Holmes R K, O'Brien A D
Department of Microbiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799.
Infect Immun. 1991 Mar;59(3):829-35. doi: 10.1128/iai.59.3.829-835.1991.
Shiga-like toxin type II (SLT-II) is one of two antigenically distinct cytotoxins produced by enterohemorrhagic Escherichia coli that are believed to play a central role in the pathogenesis of enterohemorrhagic E. coli-induced disease. SLT-II is a bipartite toxin with an enzymatically active A subunit that inhibits protein synthesis and an oligomeric B subunit that binds to the glycolipid globotriaosylceramide on eukaryotic cells. In this study, functional boundaries of the slt-II operon were mapped. Mutant proteins lacking the last four amino acids from the carboxy terminus of the 70-amino-acid mature SLT-II B polypeptide had no cytotoxic activity. However, when only two amino acids were removed from the carboxy terminus of the B subunit, the cytotoxic activity of the holotoxin was not altered drastically. Furthermore, a 21-amino-acid extension to the carboxy terminus of the SLT-II B polypeptide was tolerated with a minimum reduction in cytotoxic activity of the holotoxin. Deletion of the region coding for amino acids 3 through 18 of the 296-amino-acid mature SLT-II A polypeptide resulted in complete ablation of the cytotoxic activity of the holotoxin as well as abolition of the enzymatic activity of the A subunit. Thus, it appears that both 5'- and 3'-terminal coding sequences are essential for function of the slt-II operon.
志贺样毒素II型（SLT-II）是肠出血性大肠杆菌产生的两种抗原性不同的细胞毒素之一，据信在肠出血性大肠杆菌所致疾病的发病机制中起核心作用。SLT-II是一种双组分毒素，具有抑制蛋白质合成的酶活性A亚基和与真核细胞上的糖脂球三糖神经酰胺结合的寡聚B亚基。在本研究中，绘制了slt-II操纵子的功能边界。缺乏70个氨基酸的成熟SLT-II B多肽羧基末端最后四个氨基酸的突变蛋白没有细胞毒性活性。然而，当仅从B亚基的羧基末端去除两个氨基酸时，全毒素的细胞毒性活性并未发生显著改变。此外，在SLT-II B多肽的羧基末端延伸21个氨基酸时，全毒素的细胞毒性活性仅略有降低。缺失296个氨基酸的成熟SLT-II A多肽中编码第3至18位氨基酸的区域，导致全毒素的细胞毒性活性完全丧失，以及A亚基的酶活性丧失。因此，似乎5'和3'末端编码序列对于slt-II操纵子的功能都是必不可少的。
