Unlocking the chemical diversity of plant natural product pathways: Accessing the limonoids

解锁植物天然产物途径的化学多样性：获取柠檬苦素

• 批准号: BB/T015063/1
• 负责人: Anne Osbourn
• 金额: $ 58.19万
• 依托单位: John Innes Centre
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FT015063%2F1
• 关键词: Unlocking; chemical; diversity; plant; natural

Collectively, plants biosynthesise a vast array of natural products. Many of these are specialized metabolites that are produced by particular plant species or lineages. These metabolites likely perform important ecological functions, for example by providing protection against attach by pests and pathogens. Plant metabolic diversification is likely to be a reflection of adaptation to survival in different ecological niches.Within this proposal, we are especially interested in a large and structurally complex group of plant natural products known as limonoids. Limonoids are produced by members of the Rutaceae (Citrus) and Meliaceae (Mahogany) families. Rutaceae limonoids contribute to bitterness in citrus fruit and also have pharmaceutical potential, while Meliaceae limonoids (e.g. salannin, azadirachtin) are of interest because of their anti-insect activity. Azadirachtin (isolated from the neem tree, Azadirachta indica) is particularly well known for its potent insect antifeedant activity and environmentally friendly properties (systemic uptake, degradability, low toxicity to mammals, birds, fish, and beneficial insects). Extracts from A. indica seeds (which contain high quantities of azadirachtin) have a long history of traditional and commercial (e.g., NeemAzal-T/S, Trifolio-M GmbH) use in crop protection. Although the total chemical synthesis of azadirachtin was reported in 2007, this involved 71 steps and gave 0.00015% total yield. Chemical synthesis of azadirachtin is therefore not practical at industrial scale. Similarly, chemical synthesis of Rutaceae limonoids such as limonin (achieved in 35 steps from geraniol) is also unlikely to be commercially viable. Therefore, at present the use of Meliaceae limonoids for crop protection relies on extraction of A. indica seeds. Similarly, the potential health benefits of Rutaceae limonoids remain restricted to dietary consumption.Limonoids belong to the major class of natural products known as triterpenes. However, these compounds are non-canonical because of their unusual structures. Triterpenes typically have a 30-carbon scaffold. In contrast, the basic limonoid scaffold has only 26 carbons, which is believed to be formed from a 30-carbon 'protolimonoid' precursor by loss of four carbons and scaffold rearrangement by as yet unknown mechanisms. The 26 carbon limonoid scaffolds are heavily oxygenated and can exist as simple ring-intact structures or a highly modified derivatives in which the ring structure is broken. While considerable advances have been made in characterisation of the genes and enzymes for the biosynthesis of classical 30-carbon triterpenes, the routes to the biosynthesis of limonoids remain largely unknown, and until our recent publication in 2019 on the elucidation of the early pathway up to protolimonoids, no biosynthetic genes for limonoid production had been reported. Identifying the biosynthetic genes required for limonoid biosynthesis will enable us to understand the unprecedented biochemistry that creates the chemical diversity found within this important family of plant natural products. Metabolic engineering offers opportunities to generate crop plants with enhanced insect resistance and also to produce high-value limonoids (e.g., for pharmaceutical use) by expression in heterologous hosts. However, to achieve this the enzymes responsible for limonoid biosynthesis and diversification must first be characterized. In this proposal, we describe how we will discover how plants synthesise and diversify structurally complex limonoids. We will garner the enzymes that catalyse these processes and deploy them into our transient plant expression platform to support limonoid scaffold diversification. We will then investigate the features of these molecules that determine their anti-insect activities.

总的来说，植物生物合成了大量的天然产物。其中许多是由特定植物物种或谱系产生的专门代谢物。这些代谢物可能具有重要的生态功能，例如保护机体免受害虫和病原体的侵害。植物代谢多样化可能是适应不同生态位生存的一种反映。在这个提案中，我们特别感兴趣的是一个大型和结构复杂的植物天然产物组，称为柠檬酮。柠檬素是由芸香科（柑橘类）和桃花心木科（桃花心木）家族的成员生产的。芦花科柠檬素对柑橘类水果的苦味有贡献，也有药用潜力，而茉莉科柠檬素（如salannin，印楝素）因其抗虫活性而受到关注。印楝素（从印楝树印楝树中分离出来）因其强大的抗虫活性和环境友好特性（全身吸收、可降解、对哺乳动物、鸟类、鱼类和有益昆虫的低毒性）而闻名。印楝种子提取物（含有大量印楝素）在作物保护方面有着悠久的传统和商业应用历史（例如NeemAzal-T/S， Trifolio-M GmbH）。虽然2007年报道了印楝素的全化学合成，但共71步，总收率为0.00015%。因此，化学合成印楝素在工业规模上是不实际的。同样，化学合成芸香科类柠檬素，如柠檬素（由香叶醇35步合成）也不太可能具有商业可行性。因此，目前将苦楝科柠檬素用于作物保护主要依赖于对苦楝种子的提取。同样，芸香科类柠檬素的潜在健康益处仍然局限于饮食消费。柠檬素属于被称为三萜的天然产物的主要类别。然而，这些化合物由于其不寻常的结构而是非规范化合物。三萜通常有一个30碳的支架。相比之下，碱性类柠檬素支架只有26个碳，据信是由30个碳的“类柠檬素原”前体通过失去4个碳和支架重排而形成的，其机制尚不清楚。26碳类柠檬素支架是重氧的，可以作为简单的环完整结构或环结构断裂的高度修饰衍生物存在。虽然在经典30碳三萜生物合成的基因和酶的表征方面取得了相当大的进展，但类柠檬素的生物合成途径在很大程度上仍然未知，直到我们最近在2019年发表的关于阐明原类柠檬素的早期途径的文章之前，还没有关于类柠檬素生产的生物合成基因的报道。确定类柠檬素生物合成所需的生物合成基因将使我们能够了解前所未有的生物化学，这种生物化学创造了在这一重要的植物天然产物家族中发现的化学多样性。代谢工程为培育抗虫性增强的作物提供了机会，也为通过在异源寄主中表达产生高价值的类柠檬素（例如，用于制药）提供了机会。然而，为了实现这一目标，必须首先对负责类柠檬素生物合成和多样化的酶进行表征。在本提案中，我们描述了我们将如何发现植物如何合成和多样化结构复杂的柠檬素。我们将收集催化这些过程的酶，并将它们部署到我们的瞬时植物表达平台中，以支持类柠檬酮支架的多样化。然后我们将研究这些分子的特征，这些特征决定了它们的抗虫活性。

项目成果

Complete biosynthesis of the potent vaccine adjuvant QS-21

• DOI: 10.1038/s41589-023-01538-5
• 发表时间: 2024-01-26
• 期刊: NATURE CHEMICAL BIOLOGY
• 影响因子: 14.8
• 作者: Martin，Laetitia B. B.;Kikuchi，Shingo;Osbourn，Anne
• 通讯作者: Osbourn，Anne

Complex scaffold remodeling in plant triterpene biosynthesis.

植物三萜生物合成中的复杂支架重塑。

• DOI: 10.1126/science.adf1017
• 发表时间: 2023-01-27
• 期刊: Science (New York, N.Y.)

Limonoids on the menu.

菜单上有柠檬苦素。

• DOI: 10.1038/s41589-023-01287-5
• 发表时间: 2023
• 期刊: Nature chemical biology
• 影响因子: 14.8
• 作者: De Mattos-Shipley K

The Global Garden project: Imagining plant science

全球花园项目：想象植物科学

• DOI: 10.1002/ppp3.10133
• 发表时间: 2020
• 期刊: PLANTS, PEOPLE, PLANET
• 作者: Lee N