Biopesticides team (LPAP), Sfax, Tunisia.
FEMS Microbiol Lett. 2012 Apr;329(1):54-60. doi: 10.1111/j.1574-6968.2012.02504.x. Epub 2012 Feb 10.
Bacillus thuringiensis Cry1Ac toxin shares structurally five conserved blocs with the other δ-endotoxins. To study the role of some amino acids belonging to these regions, two mutations, Y(229) P and F(603) S, were introduced respectively in blocs 2 and 5. The stability and crystallization of the resulting mutant proteins Cry1Ac'1 and Cry1Ac'3 were affected. Both of them lost their toxicity to the Lepidopteran larvae Ephestia kuehniella. Unlike Cry1Ac'1, Cry1Ac'3 became very sensitive to proteases. Accordingly, the three-dimensional structures of the two mutants were studied. The obtained models showed that both of the residues, Y229, located near the bottom of the α7 helix, and F603, located in the core of domain III, are involved in hydrophobic interactions essential for protein stability and toxicity. These results reveal that conserved amino acids blocs of Cry toxins have conformational and functional roles.
苏云金芽孢杆菌 Cry1Ac 毒素与其他 δ-内毒素在结构上共有五个保守区域。为了研究这些区域中某些氨基酸的作用，分别在第 2 和第 5 区域引入了两个突变，Y（229）P 和 F（603）S。结果突变蛋白 Cry1Ac'1 和 Cry1Ac'3 的稳定性和结晶受到影响。它们都失去了对鳞翅目幼虫玉米螟的毒性。与 Cry1Ac'1 不同的是，Cry1Ac'3 对蛋白酶变得非常敏感。因此，对这两种突变体的三维结构进行了研究。得到的模型表明，两个残基 Y229 和 F603 都位于 α7 螺旋的底部附近和结构域 III 的核心部位，它们参与了对蛋白质稳定性和毒性至关重要的疏水相互作用。这些结果表明 Cry 毒素的保守氨基酸区域具有构象和功能作用。
