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复合体的核心成分，但其确切功能尚不清楚。通过定向诱变技术，研究了D2的特定氨基酸残基和多肽区域在光系统II复合体的功能、结构和组装中的作用。特异性突变被诱导D2。将携带位点定向突变的psbD- 1基因（编码D2）引入可转化光异养蓝藻胞杆菌6803突变体中，其中两个psbD基因拷贝（psbD- 1和psbD- 2）被删除。产生D2突变的靶区部分是通过与紫色细菌反应中心部分同源的M亚基进行比较来确定的，后者的详细结构是已知的。对突变体光系统II复合体的特性进行了多种分析，包括mRNA研究、光系统II蛋白组成和合成分析、电子传递分析、叶绿素荧光分析、特异性EPR信号分析、除草剂结合分析、闪光引起的吸光度变化。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重要但鲜为人知的蛋白质中的作用。将获得关于氧化络合物是如何组织的见解。潜在的重要意义是，蛋白质复合物可以被改变，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.***//