Design, synthesis and testing of novel phytopathogenic fungicides.

酶是一种促进反应的蛋白质，这些反应使生物能够获得生长、繁殖和维持所需的能量。要理解这类酶的结构-功能关系，一个关键的挑战是确定它的底物和抑制剂结合部位及其作用机制。对这个结合位点的性质的详细了解是重要的，因为它将揭示是否有一个共同的体系结构可以应用于底物和抑制剂结合位点，从而提供对结合机制的洞察。更重要的是，这一知识将有助于针对替代氧化酶的植物病原体和抗寄生虫药物的适当合理设计。这种替代氧化酶不仅存在于真菌和植物中，而且在人类寄生虫中也很普遍，例如布鲁氏锥虫(非洲昏睡病的病原体)、肠道寄生虫如微小隐孢子虫(导致空气传播的肠道感染隐孢子虫病)以及条件致病的人类病原体如白色念珠菌(导致念珠菌病或鹅口疮)。关于AOX在真菌中的作用，植物真菌病原菌对农用化学品的抗性是一个影响所有主要作物的国际问题。事实上，杀菌剂抗性是英国谷物种植成功的一个重要因素。据估计，英国谷物中的杀菌剂市场约为2.5亿GB(全球价值30亿美元)，其中冬小麦是主要作物。杀菌剂被用来防治许多疾病，其中最主要的一种是由小麦黑粉病引起的。用于治疗英国谷物的杀菌剂的主要化学类别包括类固醇生物合成抑制剂。在这些已被证明有效控制植物病原菌的杀菌剂中，最重要和最成功的一类是球果菊酯类杀菌剂，它们专门针对线粒体呼吸链(QO位点)，从而抑制真菌的呼吸。不幸的是，对这种杀菌剂往往产生抗药性，导致无法通过继续使用来控制真菌病原体。尽管对QO杀菌剂产生抗性的机制仍然存在争议，但越来越多的证据表明，在真菌病原菌中加入嘧菌酯等抑制剂会导致交替氧化酶(AOX)的强烈诱导。AOX是一种绕过QO位点的线粒体末端氧化酶，在胁迫诱导后在所有植物、真菌病原体和原生生物中都被诱导。我们以前已经证明了真菌植物病原体，如引起小麦主要叶斑病的真菌-小麦全蚀型真菌--小麦赤霉菌变种。当用呼吸抑制剂处理时，小黑麦具有表达AOX的能力，从而允许发展出对百菌灵具有抗药性的呼吸途径，这可能解释了百菌清杀菌剂的不同疗效。本研究的主要目的是确定含有抑制真菌交替氧化酶和/或主要呼吸链的新化合物的制剂，从而为有效控制谷类作物的真菌病害提供一种技术。我们已经设计了一些化合物(PCT/GB2015/050148和PCT/GB2013/051030)，这些化合物已经被证明是对白蜡树枯萎病菌的有效抑制剂，并证明这些化合物对小麦黑粉病也有有效的抑制作用。我们将在酵母中表达真菌rAOX酶，这将使我们不仅能够快速筛选化合物的抑制效果，而且还可以通过对真菌酶的遗传操作来确定酶对我们合成的化合物的抗药性程度。

Enzymes are proteins that facilitate the reactions that enable living organisms to acquire energy for growth, reproduction and maintenance. A key challenge in understanding the structure-function relationship of one such group of enzymes, the alternative oxidases (AOX), rests upon the identification of its substrate and inhibitor-binding site and its mechanism of action. A detailed knowledge of the nature of this binding site is important since it will reveal whether or not there is a common architecture that can be applied to substrate and inhibitor-binding sites in general and hence provide an insight into the mechanism of binding. More importantly, this knowledge will assist in the suitable rational design of phytopathogenic and anti-parasitic drugs that are specifically targeted to the alternative oxidase. The alternative oxidase is not only present in fungi and plants but also widespread amongst human parasites such as Trypanosoma brucei (the causative agent of African sleeping sickness), intestinal parasites such as Cryptosporidium parvum (responsible for an airborne intestinal infection cryptosporidiosis) and opportunistic human pathogens such as Candida albicans (causes candidiasis or 'thrush'). With respect to the role of AOX in fungi, the development of resistance to agrochemicals by plant fungal pathogens is an international problem that affects all major crops. Indeed fungicide resistance is an important factor in the successful cultivation of cereals in the UK. It is estimated that the UK market for fungicides in cereals is approximately £250M (worldwide $3bn) with winter wheat being the main crop. Fungicides are used against a number of diseases, the major one of winter wheat being caused by Septoria tritici. The main chemical classes of fungicides used to treat UK cereals include the sterol biosynthesis inhibitors. The most important and successful group of these fungicides that have proved effective in the control of plant pathogens are the strobilurin fungicides which are specifically targeted to the mitochondrial respiratory chain (Qo site) thereby inhibiting fungal respiration. Unfortunately resistance to this fungicide often develops resulting in an inability to control fungal pathogens through continued application. Although the mechanism for conferring resistance to Qo fungicides is still controversial there is growing evidence to suggest that the addition of inhibitors, such as azoxystrobin, to fungal pathogens results in a strong induction of the alternative oxidase (AOX). AOX is a mitochondrial terminal oxidase which by-passes the Qo site and is induced in all plants, fungal pathogens and protists following stress induction. We have previously demonstrated that fungal plant pathogens such as Septoria tritici, a fungus that causes major leaf spot diseases in wheat & the wheat "Take-all" fungus, Gaeumannomyces graminis var. tritici have the capacity to express AOX when treated with respiratory inhibitors thereby allowing a strobilurin-resistant respiratory pathway to develop which may account for the varying efficacy of strobilurin fungicides. The major objective of this study is to identify formulations containing novel compounds which inhibit the fungal alternative oxidase and/or the main respiratory chain thereby providing a technique for the effective control of fungal diseases in cereal crops. We have already designed a number of these compounds (PCT/GB2015/050148 & PCT/GB2013/051030) which have proved to be potent inhibitors of the Ash dieback fungus and have demonstrated that these compounds are also effective against Septoria tritici. We will express the fungal rAOX enzyme in a yeast which will enable us to not only to quickly screen the compounds inhibitory effectiveness but also through genetic manipulation of the fungal enzyme ascertain the extent to which the enzyme may become resistant to the compounds we have synthesised.