Ayra-Pardo Camilo, Davis Paul, Ellar David J
Environmental Biotechnology Laboratory, Centre for Genetic Engineering and Biotechnology (CIGB), Havana 10600, Cuba.
J Invertebr Pathol. 2007 May;95(1):41-7. doi: 10.1016/j.jip.2006.12.001. Epub 2006 Dec 30.
Bacillus thuringiensis Cry1Ac toxin is 100 times less toxic than Cry1C to Mamestra brassicae. An R(423)S mutation abolishes Cry1Ac toxin proteolysis in M. brassicae gut juice but does not increase its toxicity to this insect. The CryAAC hybrid toxin (1Ac/1Ac/1Ca) is toxic to M. brassicae but is susceptible to gut protease digestion at the R(423) residue. Accordingly we have investigated the effect of the R(423)S mutation in CryAAC on its toxicity for M. brassicae and Pieris brassicae. Bioassays demonstrated that the R(423)S mutation slightly increased the toxicity of CryAAC for M. brassicae by having a significantly inhibitory effect on the growth of surviving larvae. The mutant hybrid was still highly toxic to P. brassicae. Features of CryAACR(423)S such as, (1) stability in M. brassicae gut juice and (2) crystal solubility were investigated. Computer simulations suggest that a possible major increase in flexibility in the CryAAC loop beta7/beta8 (G(391)-P(397)) caused by the R(423)S substitution could be a reason for the increase in M. brassicae toxicity.
苏云金芽孢杆菌Cry1Ac毒素对甘蓝夜蛾的毒性比对Cry1C低100倍。R(423)S突变消除了甘蓝夜蛾肠液中Cry1Ac毒素的蛋白水解作用，但并未增加其对该昆虫的毒性。CryAAC杂合毒素（1Ac/1Ac/1Ca）对甘蓝夜蛾有毒，但在R(423)残基处易受肠蛋白酶消化。因此，我们研究了CryAAC中R(423)S突变对其对甘蓝夜蛾和粉纹夜蛾毒性的影响。生物测定表明，R(423)S突变通过对存活幼虫的生长产生显著抑制作用，略微增加了CryAAC对甘蓝夜蛾的毒性。突变杂合毒素对粉纹夜蛾仍然具有高毒性。研究了CryAACR(423)S的特性，如（1）在甘蓝夜蛾肠液中的稳定性和（2）晶体溶解性。计算机模拟表明，由R(423)S取代引起的CryAAC环β7/β8（G(391)-P(397)）柔韧性可能的主要增加可能是甘蓝夜蛾毒性增加的一个原因。
