STRUCTURE-FUNCTION RELATIONSHIP OF ISOFLAVONOID O-METHYLTRANSFERASES

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。由于它们的无根习性，植物进化出了一套复杂的次生代谢物，以保护它们免受疾病、草食和许多其他环境压力的侵害。我们正在采用蛋白质晶体学/生化遗传学相结合的方法来了解次要代谢多样性基础上的关键生物合成酶的结构和功能的细节。我们目前的研究重点涉及一组s -腺苷蛋氨酸（SAM）依赖的o -甲基转移酶，这些酶促进多酚类黄酮（类黄酮和异黄酮）的甲基化。（iso）黄酮类化合物的特定甲基化形式已被证明介导许多过程，包括抵抗紫外线照射、真菌病原体、昆虫攻击和植物根瘤菌固氮信号。我们最近从豆科模式植物紫花苜蓿（Medicago truncatula）中鉴定出一个（iso）类黄酮o -甲基转移酶（IOMTs）小家族。然而，控制其生化特性的结构基础尚未完全了解，并且这些酶在植物中发挥的催化作用仍有待确定。我们提出结合x射线晶体学和诱变方法来探索其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IOMT家族成员对（iso）类黄酮生物合成的体内功能。这些结构和功能分析将导致对（iso）类黄酮生物合成途径复杂性的分子基础有更全面的了解。

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.