Mosquitocidal Action of Bacillus thuringensis Toxins

性状（申请人提供）：苏云金芽孢杆菌亚种Israelensis（Bti）已经在田间使用了二十多年，在任何目标昆虫中没有抗性发展。相反，蚊子对B.在许多国家的田间都观察到了球腔菌。对两种杀蚊芽孢杆菌菌株产生抗性的倾向的这种显著差异可能是由于Bti中存在多种毒素。然而，蚊子能够迅速对这种菌株的个别毒素产生抗性。蚊子明显不能对Bti产生抗性的主要原因是在这种和其他杀蚊子菌株中存在细胞溶解（Cyt）毒素。在上一次资助期间，我们发现蚊子对Bti缺乏抵抗力的关键是该菌株中的两种毒素，即Cry 11 A和Cyt 1A毒素如何相互作用。我们发现Cyt 1A作为Cry 11 Aa的替代受体。重要的是，Cyt 1Aa通过Cry 11 A环结构域结合，Cry 11 A环结构域也参与结合内源性埃及伊蚊受体蛋白。我们的研究表明，伊蚊受体蛋白包括钙粘蛋白、碱性磷酸酶（ALP）和氨肽酶（APNs）。所有三个类别都以相对高的亲和力结合杀蚊毒素，不像鳞翅目昆虫中只有钙粘蛋白以高亲和力结合。这意味着蚊子的APN和ALP都可以作为初级受体，而不是像飞蛾那样作为次级受体，这表明杀蚊子和鳞翅目Cry毒素的作用方式可能存在差异。然而，我们相信Bt Cry毒素的作用模式是保守的。因此，我们假设在蚊子中发生的作用模式与鳞翅目昆虫相似。在本提案中，我们计划检验这一假设。因此，我们假设：（i）钙粘蛋白是介导与杀蚊Cry毒素的初始结合的关键蛋白质，并且对于幼虫毒性是必需的; ii）ALP（和APN）充当允许毒素靶向细胞膜的次级受体。同样在之前的提议中，我们表明Cyt 1A在充当Cry 11 Aa的替代受体方面起着关键作用。因此，我们假设（iii）Cyt 1A也是Bti中其他Cry毒素的受体，并协同杀蚊Cry毒素的毒性。我们将测试这一假设，并阐明细胞色素毒素插入膜作为替代受体的机制。该项目也是一个建议，继续三个不同的研究人员之间的成功合作，以最好地利用每个实验室的专业知识。

DESCRIPTION (provided by applicant): Bacillus thuringiensis subsp. israelensis (Bti) has been used in the field for over twenty years without resistance development in any target insect. In contrast, mosquito resistance to B. sphaericus has been observed in the field in many countries. This remarkable difference in the propensity to develop resistance to two mosquitocidal Bacillus strains is likely due to the presence of multiple toxins in Bti. However, mosquitoes are able to rapidly develop resistance to individual toxins from this strain. A major reason for the apparent inability of mosquitoes to develop resistance to Bti is the presence of cytolytic (Cyt) toxins in this and other mosquitocidal strains. During the last grant period we showed that key to the lack of mosquito resistance to Bti was how two toxins in this strain, namely Cry11A and Cyt1A toxins interact. We showed Cyt1A acts as a surrogate receptor for Cry11Aa. Importantly Cyt1Aa binds through Cry11A loop domains that are also involved in binding endogenous Aedes aegypti receptor proteins. Our research showed Aedes receptor proteins include cadherin, alkaline phosphatases (ALP), and aminopeptidases (APNs). All three classes bind mosquitocidal toxins with relatively high affinity, unlike in lepidopterans where only cadherin binds with high affinity. This implies both APN and ALP of mosquitoes could act as primary rather than as secondary receptors as in moths, suggesting a possible difference in the mode of action of mosquitocidal and lepidopteran Cry toxins. We believe however, there is conservation in the mode of action of Bt Cry toxins. Therefore we hypothesize a similar mode of action of action occurs in mosquitoes as in lepidopterans. In this proposal we plan to test this hypothesis. Consequently, we hypothesize that: (i) cadherin is a key protein which mediates initial binding to mosquitocidal Cry toxins and is essential for larval toxicity; ii) ALPs (and APNs) act as secondary receptors that allow toxin targeting to the cell membrane. Also in the previous proposal we showed Cyt1A plays a critical role in acting as a surrogate receptor for Cry11Aa. We therefore hypothesize that (iii) Cyt1A also is a receptor for other Cry toxins in Bti, and synergizes the toxicity of mosquitocidal Cry toxins. We will test this hypothesis and also elucidate the mechanism by which Cyt toxins insert into the membrane to act as surrogate receptors. This project is also a proposal to continue a successful collaboration between three different investigators to best use the expertise of each laboratory.