The D2 Protein in Photosystem II: Its Involvement in PS II Structure and Function

这个项目有几个目标，都与D2的功能有关，D2是类囊体膜上的光系统II反应中心蛋白之一。利用定点突变和基因置换技术对蓝藻聚球藻D2编码的pbsD1基因进行突变。PCC 6803，第一个目标是确定D2 C-末端附近的残基在水裂解过程和D2正确折叠中的作用。此外，还将通过对专性光异养定点定向D2突变体产生的自发光自养突变体的分析，来探索参与水分解的D2残基的三维接近。此外，对光系统II受体侧电子转移事件的定点突变研究将强调与光系统II反应中心复合体中额外的叶绿素(S)结合以及非血红素铁在光系统II中的作用有关的实验。另一个目标是与莫斯科的谢斯塔科夫博士和他的团队合作实现的，是通过随机突变psbd1来确定D2蛋白中对光系统II功能重要的其他区域。该项目的成功完成预计将显著增加关于单个氨基酸残基在膜蛋白(如D2)的功能、折叠和稳定组装中的作用的知识基础。来自太阳的能量通过光合作用过程被捕获以供生物利用。光收集过程由两个色素-蛋白质复合体完成，光系统I和II。被光系统I吸收的光能被细胞用来固定碳和产生化学能。被光系统II吸收的光能对于再生光系统I是必不可少的，光系统I会将电子损失给细胞成分。反过来，光系统II是通过分解水来再生的，这一过程释放了氧气，并解释了地球大气中存在氧气的原因。这项建议描述了一种蛋白质D2的分子研究，它是光系统II的重要组成部分。这些研究将有助于在分子水平上阐明水的分解过程。

This project has several objectives, all related to the function of D2, one of the photosystem II reaction center proteins in thylakoid membranes. Using site-directed mutagenesis and gene replacement in the D2-encoding pbsD1 gene from the cyanobacterium Synechocystis sp. PCC 6803, the first objective is to determine the role of residues near the C-terminus of D2 in the water-splitting process and in proper folding of D2. In addition, three- dimensional proximities of D2 residues involved in water splitting will be probed by analysis of spontaneous photoautotrophic mutants generated from obligate photoheterotrophic site-directed D2 mutants impaired in water splitting. Moreover, site-directed mutagenesis studies on electron transfer events at the acceptor side of photosystem II will emphasize experiments related to binding of additional chlorophyll(s) in the photosystem II reaction center complex as well as the role of the non-heme iron in photosystem II. Another objective, to be achieved in collaboration with Dr. Shestakov and his group in Moscow (USSR), is to identify other regions of the D2 protein that are important towards photosystem II function by random mutagenesis of psbD1. A successful completion of this project is anticipated to markedly increase the base of knowledge regarding the role of individual amino acid residues in function, folding and stable assembly of membrane proteins such as D2. Energy from the sun is captured for biological use by the process of photosynthesis. The process of light harvesting is carried out by two pigment-protein complexes, photosystems I and II. Light energy absorbed by photosystem I is used by the cell for carbon fixation and chemical energy production. Light energy absorbed by photosystem II is essential for regenerating photosystem I which loses electrons to cellular constituents. Photosystem II, in turn, is regenerated by the splitting of water, a process that liberates dioxygen and accounts for the presence of oxygen in the earth's atmosphere. This proposal describes molecular studies of a protein, D2, that is an essential part of photosystem II. These studies will help to elucidate how the process of water splitting occurs at the molecular level.//