Leetachewa Somphob, Moonsom Saengduen, Chaisri Urai, Khomkhum Narumol, Yoonim Nonglak, Wang Ping, Angsuthanasombat Chanan
Bacterial Protein Toxin Research Cluster, Institute of Molecular Biosciences, Mahidol University, Nakhon-Pathom 73170, Thailand.
Department of Protozoology, Faculty of Tropical Medicine, Mahidol University, Ratchathewi, Bangkok 10400, Thailand.
BMB Rep. 2014 Oct;47(10):546-51. doi: 10.5483/bmbrep.2014.47.10.192.
The insecticidal activity of Bacillus thuringiensis (Bt) Cry toxins involves toxin stabilization, oligomerization, passage across the peritrophic membrane (PM), binding to midgut receptors and pore-formation. The residues Arg-158 and Tyr-170 have been shown to be crucial for the toxicity of Bt Cry4Ba. We characterized the biological function of these residues. In mosquito larvae, the mutants R158A/E/Q (R158) could hardly penetrate the PM due to a significantly reduced ability to alter PM permeability; the mutant Y170A, however, could pass through the PM, but degraded in the space between the PM and the midgut epithelium. Further characterization by oligomerization demonstrated that Arg-158 mutants failed to form correctly sized high-molecular weight oligomers. This is the first report that Arg-158 plays a role in the formation of Cry4Ba oligomers, which are essential for toxin passage across the PM. Tyr-170, meanwhile, is involved in toxin stabilization in the toxic mechanism of Cry4Ba in mosquito larvae.
苏云金芽孢杆菌（Bt）Cry毒素的杀虫活性涉及毒素稳定、寡聚化、穿过围食膜（PM）、与中肠受体结合以及孔形成。已证明精氨酸-158和酪氨酸-170残基对Bt Cry4Ba的毒性至关重要。我们对这些残基的生物学功能进行了表征。在蚊虫幼虫中，突变体R158A/E/Q（R158）由于改变PM通透性的能力显著降低而几乎无法穿透PM；然而，突变体Y170A可以穿过PM，但在PM与中肠上皮之间的空间中降解。通过寡聚化的进一步表征表明，精氨酸-158突变体未能形成正确大小的高分子量寡聚体。这是首次报道精氨酸-158在Cry4Ba寡聚体形成中起作用，而Cry4Ba寡聚体对于毒素穿过PM至关重要。同时，酪氨酸-170在蚊虫幼虫Cry4Ba毒性机制中参与毒素稳定。
