Molecular Mechanism of Protein Transport into Chloroplasts

小行星9630459 细胞生物学中一个重要的未解决的问题是胞质合成的蛋白质如何靶向真核细胞的各个区室的问题。 在植物细胞中，叶绿体为研究这个问题提供了一个很好的系统。 大多数叶绿体蛋白质在细胞核中编码，在细胞质中合成为较高分子量的前体，并通过两个包膜膜后向输入。 这项研究的长期目标是提供一个详细的分子理解如何发生这种进口过程。 近年来，在识别和表征包含在前体蛋白中的靶向信号以及识别和表征转运装置的分子组分方面取得了重大进展。 该项目的目标是了解前体蛋白如何与运输装置的组件相互作用，以实现适当的靶向和易位。 为此，将努力实现三个具体目标。 首先是调查的超分子结构的运输组件存在于外膜的叶绿体包膜，并确定它们的排列是如何改变的前体。 第二个是调查易位接触位点的形成，将外被膜、内被膜和叶绿体基质空间中存在的转运组分聚集在一起。 这两个目标都将采用化学交联策略来稳定易位复合物，然后采用敏感的免疫学和生物化学技术来确定每个复合物的组成。 第三个目标将是研究存在于外包膜中的运输装置的两个组件的拓扑结构。 选择这两种蛋白质进行详细研究，因为它们被认为在运输装置中很重要，并且因为它们似乎具有膜蛋白的不寻常性质。 了解这些蛋白质是如何位于包膜膜最终应导致新的见解，他们如何介导的前体蛋白质的运输跨包膜膜。 了解蛋白质输入叶绿体是重要的，至少有两个原因。 首先，它增加了我们对基本细胞过程的理解，即，细胞内蛋白质运输 第二，植物体内许多经济上重要的功能发生在叶绿体中，因此，增加对蛋白质转运到叶绿体中的理解将对利用基因工程改变叶绿体内的代谢过程具有实际意义。 ***

9630459 Keegstra A significant unsolved problem in cell biology is the question of how cytoplasmically synthesized proteins are targeted to the various compartments of eukaryotic cells. In plant cells, chloroplasts offer an excellent system for studying this problem. Most chloroplastic proteins are encoded in the nucleus, synthesized in the cytoplasm as higher molecular weight precursors, and imported posttranslationally across the two envelope membranes. The long term goal of this research is to provide a detailed molecular understanding of how this import process occurs. Significant process has been made in recent years in identifying and characterizing the targeting signals contained within precursor proteins, and in identifying and characterizing the molecular components of the transport apparatus. The goal of this project is to understand how precursor proteins interact with the components of the transport apparatus to achieve proper targeting and translocation. To this end, three specific objectives will be pursued. The first is to investigate the supramolecular structure of transport components present in the outer membrane of the chloroplast envelope and determine how their arrangement is altered by precursors. The second is to investigate the formation of translocation contact sites that bring together transport components present in the outer envelope membrane, the inner envelope membrane and in the chloroplastic stromal space. Both of these objectives will be pursued using chemical cross-linking strategies to stabilize translocation complexes, followed by sensitive immunological and biochemical techniques to determine the composition of each complex. The third objective will be to investigate the topology of two components of the transport apparatus present in the outer envelope membrane. These two proteins were chosen for detailed study because they are thought to be important in the transport apparatus and because they appear to have unusual properties for membrane p roteins. Understanding how these proteins are situated in the envelope membrane should eventually lead to new insights into how they mediate the transport of precursor proteins across the envelope membranes. %%% Understanding protein import into chloroplasts is important for at least two reasons. First, it adds to our understanding of a basic cellular process, i.e., intracellular protein trafficking. Second, many economically important functions within plants occur in the chloroplasts, and therefore an increased understanding of protein transport into chloroplasts will have practical significance for efforts to employ genetic engineering to alter the metabolic processes inside chloroplasts. ***