STRUCTURE-FUNCTION RELATIONSHIP OF ISOFLAVONOID O-METHYLTRANSFERASES

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。由于固着的习性，植物进化出一套复杂的次生代谢产物来保护它们免受疾病、草食和许多其他环境胁迫的影响。我们正在使用蛋白质结晶学/生化遗传学相结合的方法来了解构成次生代谢多样性的关键生物合成酶的结构和功能的细节。我们目前的重点涉及一组依赖S腺苷蛋氨酸的O-甲基转移酶，这种酶促进多酚(异黄酮类和异黄酮类)的甲基化。特定甲基化形式的(Iso)类黄酮已被证明参与许多过程，包括对紫外线照射的抗性、真菌病原体、虫害以及植物根瘤菌对氮气固定的信号转导。我们最近从豆科模式植物紫花苜蓿中发现了一个小的(Iso)类黄酮氧甲基转移酶(IOMTs)家族。然而，控制它们的生化性质的结构基础还不完全清楚，这些酶在植物中所起的催化作用还有待确定。我们提出了一种X射线结晶学和诱变相结合的方法来探索它们区域特异性和立体选择性甲基化的结构基础。我们还建议使用反向遗传学和代谢谱来评估特定的IOMT家族成员在体内对(Iso)类黄酮生物合成的功能。这些结构和功能的分析将导致对(Iso)类黄酮生物合成途径复杂性的分子基础的更全面的理解。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Due to their sessile habit, plants have evolved a complex set of secondary metabolites to protect them from diseases, herbivory and many other environmental stresses. We are employing a combined protein crystallographic/biochemical-genetics approach to understand the details of structures and functions of the key biosynthetic enzymes that underlie the diversity of secondary metabolism. Our current focus involves a group of S-adenosylmethionine (SAM) dependent O-methyltransferases, enzymes that facilitate methylation of polyphenolic (iso)flavoniods (flavonoids and isoflavonoids). Specific methylated forms of (iso)flavonoids have been shown to mediate many processes including resistance to UV irradiation, fungal pathogens, insect attack, and plant-rhizobium signaling for N2 fixation. We recently identified a small family of (iso)flavonoid O-methyltransferases (IOMTs) from the legume model plant Medicago truncatula. However the structural underpinnings governing their biochemical properties are not completely understood, and the catalytic roles these enzymes play in planta remain to be defined. We propose a combined X-ray crystallographic and mutagenesis approach to explore the structural basis for their regiospecific and stereoselective methylations. We also propose to use reverse genetics and metabolic profiling to assess the in vivo functions of the specific IOMT family members for (iso)flavonoid biosynthesis. These structure and function analyses will lead to a more complete understanding of the molecular basis that underlies the complexity of (iso)flavonoid biosynthetic pathways.