Structural and Functional Analysis of the Plant Phenylpropanoid Biosynthetic Pathway

本研究的目的是了解植物苯丙烷类化合物生物合成的酶机制。本研究采用了一种全面的实验方法，在分子水平上，旨在了解的结构和功能的基础上参与苯丙素类生物合成途径的酶的催化性能。该项目的长期目标是使用来自蛋白质X射线晶体学的原子分辨率酶结构作为合理操纵生物合成途径中单个生物合成酶和多种酶的底物和产物特异性的起点。这项工作集中在苜蓿中苯丙烷类化合物产生的一组分支途径上。 特别是，这项建议的重点是完成的三维X-射线晶体结构的几种酶参与的生物合成的诱导剂和植物抗毒素。 此外，还将对具有结构特征的酶进行功能实验。 这些后面的实验的重点将是揭示核心的机制原则，管理的底物和产品的特异性，每种酶。 目前的目标是（1）扩大植物聚酮脱氢酶，查耳酮合酶，（2）芪合酶，和吡喃酮合酶的结构和功能分析;和（3）解决X-射线晶体结构的查耳酮异构酶，然后通过额外的功能实验来调节这些酶的特异性。 这些研究将阐明植物中苯丙素类化合物产生的酶机制。 此外，该实验策略采用蛋白质X射线晶体学，定点和饱和诱变的单个和多个氨基酸的位置，从同源家族的生物合成酶，小分子鉴定，和动力学分析收集的序列信息将作为起点的合理操作的底物和产品的特异性的个别生物合成酶和多个酶的生物合成途径。 植物苯丙素类化合物是由植物在受到真菌、细菌和病毒等感染因子的挑战时合成的一组不同的化学物质。 这些复杂的小分子在植物与周围环境的相互作用中也起着至关重要的作用。这类天然产物包括水杨酸盐、木脂素、绿原酸、香豆素、芪类和类黄酮。 类黄酮组包括异黄酮、紫檀烷、黄酮、黄酮醇和花青素。 这种分子多样性是由于被称为酶的高度特异性生物催化剂的作用而产生的。 这些化合物在植物中的用途变化很大，包括作为结构聚合物、防御屏障、响应微生物、昆虫和草食动物捕食而合成的防御化学物质、固氮根瘤菌的信号分子、UV保护剂和色素的作用。 除了它们在植物生理学中的作用之外，苯丙素类化合物还具有许多已被证明对制药、食品、农业和营养工业有用的性质。 特别地，许多植物衍生的苯丙素类是有价值的药用剂。 此外，常规膳食摄入类苯丙酸衍生的化合物，包括木脂素、芪类和甘草酸，具有相当大的健康益处。 该项目利用一种称为蛋白质x射线晶体学的技术来破译负责创造苯丙素小分子的重要植物催化剂的三维形状。 然后使用这些信息来了解和改变这些催化剂的特异性，以便在这些生物合成系统中创造更大的分子多样性。 这些酶的底物和产物特异性的调节将直接影响生产具有治疗和农业意义的新型化合物的努力。

The goal of this project is to understand the enzymatic mechanisms underlying the biosynthesis of plant phenylpropanoids. This research employs a comprehensive experimental approach on the molecular level aimed at understanding the structural and functional basis for the catalytic properties of enzymes involved in phenylpropanoid biosynthetic pathways. The long-term objective of this project is to use atomic resolution enzyme structures derived from protein x-ray crystallography as starting points for the rational manipulation of both the substrate and product specificity of individual biosynthetic enzymes and multiple enzymes in biosynthetic pathways. The work centers on a branched set of pathways for phenylpropanoid production in alfalfa. In particular, this proposal focuses on the completion of the three-dimensional x-ray crystal structures of several enzymes involved in the biosynthesis of nodulation inducers and phytoalexins. In addition, functional experiments on the structurally characterized enzymes will be carried out. The emphasis of these latter experiments will be to uncover the core mechanistic principles governing the substrate and product specificity of each enzyme. The current objectives are (1) to expand the structural and functional analysis of the plant polyketide synthases, chalcone synthase, (2) stilbene synthase, and pyrone synthase; and (3) to solve the x-ray crystallographic structure of the enzyme chalcone isomerase followed by additional functional experiments to modulate the specificity of these enzymes. These studies will elucidate the enzymatic mechanisms governing phenylpropanoid production in plants. In addition, this experimental strategy employing protein x-ray crystallography, site-directed and saturation mutagenesis of single and multiple amino acid positions, sequence information gathered from homologous families of biosynthetic enzymes, small molecule identification, and kinetic analyses will serve as starting points for the rational manipulation of the substrate and product specificity of individual biosynthetic enzymes and multiple enzymes in biosynthetic pathways. Plant phenylpropanoids are a diverse group of chemicals synthesized by plants when they are challenged with infectious agents such as fungi, bacteria, and viruses. These complex small molecules also play vital roles in the interaction of plants with their surrounding environment. This family of natural products includes salicylates, lignans, chlorogenic acid, coumarins, stilbenes, and flavonoids. The flavonoid group encompasses isoflavones, pterocarpans, flavones, flavonols, and anthocyanins. This molecular diversity arises due to the action of highly specific biological catalysts known as enzymes. The utility of these compounds in plants varies widely and includes roles as structural polymers, defense barriers, defense chemicals synthesized in response to microbial, insect, and herbivore predation, signaling molecules for nitrogen-fixing rhizobia bacteria, UV-protective agents, and pigments. In addition to their role in plant physiology, phenylpropanoids possess a number of properties that have proven useful to the pharmaceutical, food, agricultural, and nutritional industries. In particular, a number of plant-derived phenylpropanoids are valuable medicinal agents. Moreover, the regular dietary consumption of phenylpropanoid-derived compounds including lignans, stilbenes, and isoflavonoids has considerable health benefits. This project utilizes a technique known as protein x-ray crystallography to decipher the three dimensional shapes of the vital plant catalysts responsible for creating phenylpropanoid small molecules. This information is then used to understand and alter the specificity of these catalysts in order to create even greater molecular diversity in these biosynthetic systems. Modulation of the substrate and product specificity of these enzymes will directly impact efforts to produce novel compounds of both therapeutic and agricultural interest.