Use of Mutants to Study Biogenesis and Functions of the Reaction Center Proteins of Photosystem I

本课题主要研究多亚单位蛋白复合体光系统I （PSI）。PSI定位于蓝藻、藻类和植物的类囊体膜，是光合作用电子传递链的一个组成部分，并介导从质体青素或细胞色素c6到低电位受体（如铁氧还蛋白）的跨膜电子转移。PSI是一种含有11个多肽成分的大色素蛋白。此外，该蛋白复合体中还存在醌类、铁硫中心、类胡萝卜素和近100种叶绿素等辅助因子。来自蓝藻的PSI复合体已经结晶，其结构目前以4.5 a的分辨率已知。该项目的长期目标是从分子角度了解PSI的生物发生和功能。实验生物是Synechocystis 6803，这是一种单细胞的，自然可转化的蓝藻，它提供了一个通用的遗传系统来研究这种蛋白质复合物。PI的实验室最近在Synechocystis 6803中发现了一种新的蛋白质BtpA，它不是PSI的结构成分，而是调节其催化活性核心复合物的组装。该项目的具体目的是：(1)确定BtpA蛋白的细胞位置。(2)通过分离和分析BtpA突变体中恢复PSI核心复合物组装的抑制突变体来阐明BtpA的功能。(3)探讨BtpA是否是一种膜结合分子伴侣。(4)检测BtpA是否作为翻译激活蛋白。(5)阐明PSI组装中BtpA突变体温度敏感性的基础。通过收集太阳辐射，PSI综合体为我们世界上一半的生物质生产提供了能源。大多数，如果不是全部，结构蛋白以及PSI的氧化还原成分已经被确定。目前的挑战是了解控制这种膜蛋白复合物的化学计量组装和功能的机制。在这个项目中，将结合遗传学、生物化学和生物物理学的工具来追求这一挑战。了解这种超分子复合物的生物发生和功能也将对了解其他生物膜中这种大蛋白质复合物的一般知识做出重要贡献。＊＊＊

9632162 Pakrasi This proposal is focused on the study of the multisubunit protein complex Photosystem I (PSI). Localized in the thylakoid membranes of cyanobacteria, algae and plants, PSI is an integral component of the photosynthetic electron transport chain, and mediates transmembrane electron transfer from plastocyanin or cytochrome c6 to low potential acceptors such as ferredoxin. PSI is a large pigment-protein with eleven polypeptide components. In addition, cofactors such as quinones, iron sulfur centers, carotenoids and nearly 100 chlorophylls are present in this protein complex. The PSI complex from cyanobacteria has been crystallized and its structure is currently known at a resolution of 4.5 A. The long range goal of this project is to understand, in molecular terms, the biogenesis and function of PSI. The experimental organism is Synechocystis 6803, a unicellular, naturally transformable cyanobacterium, that offers a versatile genetic system to study this protein complex. The PI's lab has recently identified BtpA, a novel protein in Synechocystis 6803, that is not a structural component of PSI, but regulates the assembly of its catalytically active core complex. The specific aims of this project are: (1) To determine the cellular location of the BtpA protein. (2) To elucidate the function of BtpA by isolating and analyzing suppressor mutants that restore the assembly of the PSI core complex in btpA mutants. (3) To investigate whether BtpA is a membrane-bound molecular chaperone. (4) To examine whether BtpA acts as a translational activator protein. (5) To elucidate the basis for temperature sensitivity of a BtpA mutant in the assembly of PSI. %%% By harvesting solar radiation, the PSI complex provides half of the energy for biomass production in our world. Most, if not all, of the structural proteins as well as the redox components of PSI have been identified. The current challenge is to understand the mechanisms that control the stoichiometric assembly and function of this membra ne protein complex. During this project, tools of genetics, biochemistry and biophysics will be combined to pursue this challenge. Understanding the biogenesis and function of this supramolecular complex will also make important contributions to the general knowledge about such large protein complexes in other biological membranes. ***