Lockey T D, Ourth D D
Department of Biology, Division of Molecular Sciences and Microbiology, University of Memphis, TN 38152, USA.
Eur J Biochem. 1996 Feb 15;236(1):263-71. doi: 10.1111/j.1432-1033.1996.00263.x.
The insect humoral defense system produces antibacterial peptides called cecropins. Cecropins were initially isolated from Hyalophora cecropia pupae and have since been isolated and identified in various insects. In this study, we have isolated and identified a cecropin from Heliothis virescens larvae. Rabbit IgG were raised against synthetic cecropin B. Affinity chromatography with the rabbit anti-(cecropin B) IgG was used to isolate a cecropin from hemolymph of H. virescens larvae. Acid gel electrophoresis followed by a bacterial-overlay analysis showed that Heliothis cecropin is a basic peptide of low molecular mass with bactericidal activity against Escherichia coli K12 D31. Heliothis cecropin is therefore analogous to synthetic cecropin B. One unresolved issue concerning cecropins and other antibiotic peptides is the mode of action by which they kill bacteria. By means of electron microscopy and immunocytochemistry with gold-labeled rabbit anti-cecropin IgG, binding of purified and synthetic cecropin to the cell membranes of E. coli K12 D31 cells was observed. Small lesions in the cell membrane were seen that had a diameter of 9.6 nm and internal pore of 4.2 nm. The Heliothis cecropin was found to be a pore-forming molecule that causes lesions in the cell membrane of E. coli K12 D31. The lesions lead to leakage of cytoplasmic contents and death of bacteria.
昆虫体液防御系统会产生一种名为天蚕素的抗菌肽。天蚕素最初是从樗蚕蛹中分离出来的，此后在各种昆虫中都有被分离和鉴定。在本研究中，我们从烟芽夜蛾幼虫中分离并鉴定出了一种天蚕素。用合成的天蚕素B免疫家兔制备兔IgG。利用兔抗（天蚕素B）IgG进行亲和层析，从烟芽夜蛾幼虫的血淋巴中分离出一种天蚕素。酸性凝胶电泳后进行细菌覆盖分析表明，烟芽夜蛾天蚕素是一种低分子量的碱性肽，对大肠杆菌K12 D31具有杀菌活性。因此，烟芽夜蛾天蚕素与合成的天蚕素B类似。关于天蚕素和其他抗生素肽的一个尚未解决的问题是它们杀死细菌的作用方式。通过电子显微镜和用金标记兔抗天蚕素IgG进行免疫细胞化学分析，观察到纯化的和合成的天蚕素与大肠杆菌K12 D31细胞膜的结合。在细胞膜上发现了直径为9.6纳米、内部孔径为4.2纳米的小损伤。发现烟芽夜蛾天蚕素是一种形成孔道的分子，它会在大肠杆菌K12 D31的细胞膜上造成损伤。这些损伤导致细胞质内容物泄漏和细菌死亡。
