植物5-氨基乙酰丙酸合成中GluTR及其调控蛋白的结构基础

5-氨基乙酰丙酸（ALA）是植物的四吡咯（如叶绿素和血红素）生物合成途径中第一个重要分子，是对四吡咯合成进行调控的重要节点。ALA由谷氨酸经过GluRS、GluTR和GSA-AT三个酶催化生成，其中GluTR催化的还原反应是ALA合成的限速步骤。对GluTR活性的调控是植物对ALA合成调节的关键。植物叶绿体中仅有一个GluTR，其调控元件包括：负调控因子FLU和四吡咯合成的终产物血红素抑制GluTR的活性；GluTRBP通过结合GluTR，分配ALA至不同的四吡咯合成途径。此外，GluTR下游的GSA-AT被认为与GluTR形成分子间通道，以确保GluTR的不稳定产物转化为ALA。本项目拟结合结构生物学、生物化学以及植物生理学的方法，全面阐述植物中以GluTR为靶点的ALA生物合成的调控机理，从蛋白质水平上揭示植物生理功能调节的分子基础，为更好的了解和改造植物提供理论依据。

5-aminolevulinic acid (ALA) is the first important molecule in tetrapyrrole (such as chlorophyll and heme) biosynthesis pathways in plants, which makes it a critical control point in tetrapyrrol biosynthesis. ALA is converted from glutamic acid by three sequential reactions catalyzed by GluRS, GluTR and GSA-AT, respectively, and the glutamyl-tRNA reduction catalyzed by GluTR is the rate-limiting step in ALA synthesis. Therefore, controlling GluTR activity is a key to regulate ALA synthesis in plants. Only one GluTR has been found in chloroplast, and its regulatory components have been characterized as the following: both the negative regulator protein FLU and one end product, heme, inhibit GluTR activity; GluTRBP organizes ALA synthesis into separated pathways for balanced synthesis of heme and chlorophyll by binding to GluTR. Besides, the downstream enzyme GSA-AT is proposed to form an intermolecular channel with GluTR to ensure the direct transfer of unstable GSA, the product of GluTR, to GSA-AT. Our goal is, by using a combination of structural biological, biochemical and plant physiological methods, to elucidate the regulation mechanism of ALA synthesis via GluTR in plants, and thus to reveal such physiological regulation at the molecular level, and to provide clues for further understanding and modifying plants.