Bacillus thuringiensis (Bt) Cry1Fa and Cry1Ab proteins are important Cry toxins due to their high, selective toxicity against a number of lepidopteran species, including important pests of corn and cotton. Competition binding assays are a classical tool for investigating Cry toxin interactions with target pest insects. We developed a fluorescence-based binding assay and assessed Cry1Fa and Cry1Ab toxin binding to brush border membrane preparations from lepidopteran corn pests including Ostrinia nubilalis (European corn borer, ECB), Diatraea grandiosella (south western corn borer, SWCB), and Helicoverpa zea (corn earworm, CEW). Homologous and heterologous competition binding assays with fluorophore-(Alexa488)-labeled Cry1Fa toxin showed that Cry1Fa shares binding site(s) with Cry1Ab toxin in ECB, and SWCB for which Cry1Ab has higher affinity than Cry1Fa. Apart from the shared binding sites, Cry1Ab and Cry1Fa bind an additional site(s) in ECB and SWCB. In CEW, Cry1Fa and Cry1Ab each, has a high affinity binding site(s), which binds the heterologous toxin with low affinity. The Cry1Ab-Cry1Fa toxin binding models for ECB, SWCB and CEW based on our results are considered in the context of what is known about acquired cross-resistance against Cry1Ab and Cry1Fa toxins.

中文翻译：

---

苏云金芽孢杆菌 Cry1Fa 和 Cry1Ab 毒素结合位点在 Ostrinia nubilialis (Hübner)、Diatraea grandiosella (Dyar) 和 Helicoverpa zea (Boddie) 幼虫刷状缘膜囊泡上的荧光分析

苏云金芽孢杆菌 (Bt) Cry1Fa 和 Cry1Ab 蛋白是重要的 Cry 毒素，因为它们对许多鳞翅目物种（包括玉米和棉花的重要害虫）具有高选择性毒性。竞争结合分析是研究 Cry 毒素与目标害虫相互作用的经典工具。我们开发了一种基于荧光的结合测定，并评估了 Cry1Fa 和 Cry1Ab 毒素与鳞翅目玉米害虫包括 Ostrinia nubilalis（欧洲玉米螟，ECB）、Diatraea grandiosella（西南玉米螟，SWCB）和 Helicoverpa zea（玉米穗虫，CEW）。用荧光团 (Alexa488) 标记的 Cry1Fa 毒素进行同源和异源竞争结合测定表明，Cry1Fa 与 ECB 中的 Cry1Ab 毒素共享结合位点，Cry1Ab 的亲和力高于 Cry1Fa 的 SWCB。除了共享的结合位点外，Cry1Ab 和 Cry1Fa 还结合了 ECB 和 SWCB 中的其他位点。在 CEW 中，Cry1Fa 和 Cry1Ab 均具有高亲和力结合位点，以低亲和力结合异源毒素。基于我们的结果，ECB、SWCB 和 CEW 的 Cry1Ab-Cry1Fa 毒素结合模型是在已知的对 Cry1Ab 和 Cry1Fa 毒素的获得性交叉抗性的背景下考虑的。