Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, P.O. Box 8146 Dep., N-0033 Oslo, Norway.
Infect Immun. 2010 Sep;78(9):3813-21. doi: 10.1128/IAI.00247-10. Epub 2010 Jul 12.
This study focuses on the interaction of the three components of the Bacillus cereus Nhe enterotoxin with particular emphasis on the functional roles of NheB and NheC. The results demonstrated that both NheB and NheC were able to bind to Vero cells directly while NheA lacked this ability. It was also shown that Nhe-induced cytotoxicity required a specific binding order of the individual components whereby the presence of NheC in the priming step as well as the presence of NheA in the final incubation step was mandatory. Priming of cells with NheB alone and addition of NheA plus NheC in the second step failed to induce toxic effects. Furthermore, in solution, excess NheC inhibited binding of NheB to Vero cells, whereas priming of cells with excess NheC resulted in full toxicity if unbound NheC was removed before addition of NheB. By using mutated NheC proteins where the two cysteine residues in the predicted beta-tongue were replaced with glycine (NheCcys-) or where the entire hydrophobic stretch was deleted (NheChr-), the predicted hydrophobic beta-tongue of NheC was found essential for binding to cell membranes but not for interaction with NheB in solution. All data presented here are compatible with the following model. The first step in the mode of action of Nhe is associated with binding of NheC and NheB to the cell surface and probably accompanied by conformational changes. These events allow subsequent binding of NheA, leading to cell lysis.
本研究重点关注蜡样芽胞杆菌 Nhe 肠毒素的三个组成部分的相互作用，特别强调 NheB 和 NheC 的功能作用。结果表明，NheB 和 NheC 均能够直接与 Vero 细胞结合，而 NheA 则缺乏这种能力。还表明，Nhe 诱导的细胞毒性需要各个成分的特定结合顺序，其中 NheC 在启动步骤中的存在以及 NheA 在最终孵育步骤中的存在是必需的。单独用 NheB 预孵育细胞以及在第二步中添加 NheA 和 NheC 并不能诱导毒性作用。此外，在溶液中，过量的 NheC 抑制 NheB 与 Vero 细胞的结合，而用过量的 NheC 预孵育细胞，如果在添加 NheB 之前除去未结合的 NheC，则会导致完全毒性。通过使用突变的 NheC 蛋白，其中预测的β舌中的两个半胱氨酸残基被甘氨酸取代（NheCcys-）或整个疏水区被删除（NheChr-），发现预测的 NheC 的疏水性β舌对于与细胞膜结合是必需的，但对于在溶液中与 NheB 的相互作用则不是必需的。这里呈现的所有数据都与以下模型一致。Nhe 作用模式的第一步与 NheC 和 NheB 与细胞表面的结合有关，可能伴随着构象变化。这些事件允许随后 NheA 的结合，导致细胞裂解。
