The Role of the D2 Protein in the Photosystem II Complex as Probed by Directed Mutagenesis and Mutant Analysis

D2蛋白是光合膜中光系统II复合体的中心成分，但其确切功能尚不清楚。D2的特定氨基酸残基和多肽区在光系统II复合体的功能、结构和组装中的作用正在用定向突变技术进行研究。特定的突变被诱导为D2。将编码D2的psbD-I基因导入可转化光异养蓝藻聚球藻6803的突变体中，两个psbD基因拷贝(psbD-I和psbD-II)已被缺失。产生D2突变的靶区部分是通过与紫色细菌反应中心的部分同源M亚单位进行比较来确定的，后者的详细结构已知。对突变的光系统II复合体的性质进行了多种分析，包括mRNA研究、光系统II蛋白的组成和合成分析、电子传递、叶绿素荧光、特异的EPR信号、除草剂结合和闪光诱导的吸光度变化。该项目的结果将导致详细了解特定残基和区域在光合膜中一种重要但知之甚少的蛋白质中的作用。我们将深入了解氧化复合体是如何组织起来的。潜在的重要意义在于，蛋白质复合体可以被改变，从而导致更有效的操作。

The D2 protein is a central component of the Photosystem II complex in photosynthetic membranes, but its precise function is unknown. The role of specific amino acid residues and polypeptide regions of D2 in function, structure and assembly of the Photosystem II complex is being studied by directed mutagenesis techniques. Specific mutations are induced D2. The psbD-I gene (encoding D2) carrying site-directed mutations is introduced into a mutant of the transformable photoheterotrophic cyanobacterium Synechocystis 6803, from which the two psbD gene copies (psbD-I and psbD-II) have been deleted. Target regions to create D2 mutations are identified in part by comparison with the partially homologous M subunit of the reaction center from purple bacteria, for which the detailed structure is known. The properties of the mutant Photosystem II complex are analyzed in a variety of ways, including mRNA studies, and analysis of Photosystem II protein composition and synthesis, electron transport, chlorophyll fluorescence, specific EPR signals, herbicide binding, and flash-induced absorbance changes. The results of this project will lead to a detailed understanding of the role of specific residues and regions in an important but poorly understood protein in photosynthetic membranes. Insight will be gained on how the oxidizing complex is organized. Potentially significant is that the protein complex can be altered to result in more efficient operation.***//