Molecular Mechanism of Protein Transport into Chloroplasts

植物细胞中许多重要的代谢途径都发生在叶绿体内。虽然这些过程所需的一些蛋白质和酶是在叶绿体内部合成的，但绝大多数这些蛋白质是在植物细胞的细胞质中作为前体合成的，随后被转运到叶绿体中。这些蛋白质进入叶绿体是由位于叶绿体表面的输入装置介导的。该项目的长期目标是确定构成模式植物Arabadopsis进口装置的蛋白质，并阐明进口装置中的单个蛋白质促进前体蛋白质向叶绿体运输的生化机制。本项目使用遗传方法来研究作为进口机器分子马达的选定蛋白质的功能，通过为运输过程提供驱动力。在转基因植物中，正常的Arabadopsis蛋白要么被灭活，要么被一种改变形式的蛋白所取代。细胞生物学和生物化学实验将被用来评估基因改变对转运过程的影响。转运过程将在表达一种改变蛋白或多种改变蛋白的植物中进行研究。这一策略将阐明单个蛋白质的功能，并提供各种蛋白质之间相互作用的信息。该项目对蛋白质输入的新认识将有助于各种叶绿体特异性代谢途径的工程设计。例如，合成独特脂肪酸的新型酶可以靶向叶绿体，以创造具有改良脂肪酸的植物，这些脂肪酸具有更高的营养或工业价值。因此，这项研究将促进我们对蛋白质靶向叶绿体的基本理解，并通过提高我们设计和修饰植物的各种用途的能力产生实际影响。

Many essential metabolic pathways in plant cells occur within the chloroplast. Although some of the proteins and enzymes required for these processes are synthesized within the chloroplast itself, the vast majority of these proteins are synthesized as precursors in the cytoplasm of plant cells and are subsequently transported into chloroplasts. Import of these proteins into chloroplasts is mediated by an import apparatus located on the chloroplast surface. The long-term goal of this project is to identify the proteins that constitute the import apparatus of the model plant Arabadopsis and to clarify the biochemical mechanisms by which individual proteins of the import apparatus contribute to the transport of precursor proteins into chloroplasts. This project uses a genetic approach to investigate the function of selected proteins that operate as the molecular motor of the import machinery, by providing the driving force for the transport process. Transgenic plants will be constructed in which the normal Arabadopsis protein has been either inactivated or replaced with an altered form of the protein. Cell biological and biochemical experiments will then be used to evaluate the effect of the gene alterations on the transport process. The transport process will be studied in plants expressing either one altered protein or multiple altered proteins. This strategy will elucidate the functions of individual proteins and also provide information about interactions between the various proteins. The new understanding of protein import derived from this project will be useful for efforts that involve the engineering of various chloroplast-specific metabolic pathways. For instance, novel enzymes that synthesize unique fatty acids could be targeted to chloroplasts to create plants with modified fatty acids that have improved nutritional or industrial value. Hence, this research will both advance our basic understanding of protein targeting to chloroplasts and have the practical impact by improving our ability to engineer and modify plants for a variety of uses.