Plant Terpene Metabolism: Monoterpene Hydroxylases and Sesquiterpene Cyclases

大多数单萜和倍半萜是由焦磷酸戊烯基环化成烯烃，然后由细胞色素p450依赖的羟基化引发氧化修饰而得到的。对两种物理性质和反应复杂性不同的倍半萜环化酶进行研究，将验证相同的活性位点残基在该酶类型的亲电机制中发挥相似作用的假设。对三种密切相关的(-)-柠檬烯羟化酶的研究，这些酶在这种简单的单萜烯烯烃烯丙基羟基化的位置不同，将检验活性位点地形的微小变化是这些细胞色素P450酶的氧插入区域化学的基础。均相蛋白将用于产生抗体和部分氨基酸序列，并采用分子克隆和表达策略获得完整的初级序列和更大量的酶。放射性修饰试剂将用于选择性地标记环化酶的活性位点半胱氨酸和组氨酸残基，光降解底物类似物将用于标记环化酶和羟化酶位点的疏水区域。活性位点肽将被制备，测序，比较，并定位在蛋白质上。特定残基在环化酶催化中的作用将通过使用代表不同底物结合域的类似物来防止化学修饰和定向诱变来确定。柠檬烯拴系血红素定向抑制剂，以及19F-NMR方法，将用于探索细胞色素的血红素铁和柠檬烯底物之间的空间关系。这些研究将对这些新型环化酶和羟化酶催化剂的性质提供新的信息，并对萜类天然产物的来源有更清晰的认识。萜类化合物在植物与环境的相互作用中起着重要作用。对萜类生物化学的了解将使我们更深入地了解这些化合物在植物中的作用。除了商业上众所周知的树脂精油外，正在认真考虑将这些植物代谢物作为能源密集型化学品的可再生来源的非传统用途。广泛的萜类化合物具有药理意义，许多具有农化用途。从这项工作中获得的新知识将有助于努力增加这些有价值的植物代谢物的产量

Most monoterpenes and sesquiterpenes are derived by cyclization of prenyl pyrophosphates to olefins followed by oxidative modification initiated by cytochrome P450-dependent hydroxylation. Studies with two sesquiterpene cyclases, differing in physical properties and reaction complexity, will test the hypothesis that the same active site residues play similar roles in the electrophilic mechanism of this enzyme type. Studies with three closely-related (-)-limonene hydroxylases, that differ in position of allylic hydroxylation of this simple monoterpene olefin, will test the proposal that minor alterations in active site topography underlie regiochemistry of oxygen insertion by these cytochrome P450 enzymes. Homogeneous proteins will be used to generate antibodies and partial amino acid sequences, and a molecular cloning and expression strategy adopted to obtain complete primary sequences and larger amounts of the enzymes. Radioactive modifying reagents will be employed to selectively label active site cysteine and histidine residues of the cyclases, and photolabile substrate analogs will be utilized to label hydrophobic regions of both cyclase and hydroxylase sites. Active site peptides will be prepared, sequenced, compared, and located on the proteins. The role of specific residues in cyclase catalysis will be determined by protection against chemical modification using analogs representing different substrate binding domains, and by directed mutagenesis. Limonene-tethered heme- directed inhibitors, as well as 19F-NMR methods, will be used to probe the spatial relationship between the heme iron of the cytochromes and the limonene substrate. These studies will provide new information on the nature of these novel cyclase and hydroxylase catalysts and a clearer understanding of the origin of terpenoid natural products. Terpenoids play an important role in the interaction of the plant with its environment. An understanding of terpenoid biochemistry will allow a deeper understanding of the role of these compounds in plants. In addition to the well known essential oils of resins of commerce, serious consideration is being given to nontraditional uses of these plant metabolites as renewable sources of energy- intensive chemicals. A broad range of terpenoids are of pharmacological significance and many are of agrochemical utility. New knowledge gained from this work will assist in efforts to increase the production of these valuable plant metabolites.//