Assembly and Function of the Cyanobacterial Water-Oxidation Complex

蓝藻水氧化复合物的组装和功能

• 批准号: 9728754
• 负责人: Robert Burnap
• 金额: $ 30万
• 依托单位: Oklahoma State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-03-01 至 2002-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9728754&HistoricalAwards=false
• 关键词: Assembly; Function; Cyanobacterial; Water; Oxidation

9728754 Burnap The focus of this project is on the structure and assembly of the catalytic site of the photosynthetic water-oxidation reaction. The work combines molecular genetic, biochemical and biophysical approaches to clarify the process of photoactivation, which is the sequential light-dependent assembly of the catalytic tetramer of manganese atoms that forms the core of the water-oxidation complex. Photoactivation represents a fascinating problem of metalloprotein assembly. It is a multi-quantum process involving a sequence of kinetically resolvable molecular rearrangements that are stabilized by the photooxidation of manganese and binding of calcium. The molecular events occurring during this process remain obscure and the major object of this research is to define these events in terms of the influence of the protein groups providing the coordination environment for the incoming manganese and calcium ions during the assembly sequence. The research is facilitated by the availability of numerous partially impaired site-directed mutants of putative manganese and calcium ligands in the intrinsic portion of the complex and mutants of the extrinsic polypeptides, which have been shown to modulate the efficiency of the assembly process. Polarographic and fluorescence methods of monitoring the assembly process are utilized. Earlier studies of photoactivation using intact mutant cyanobacterial cells are now extended to in vitro studies where analysis of the cofactor requirements of normal and genetically modified reaction center core complexes can be studied in greater detail. Photosynthesis is a globally important process that has a number of crucial unresolved features. Among the most puzzling aspects of the photosynthetic mechanism is oxygen production by the PSII water-splitting enzyme. PSII is of critical importance from both the agricultural and ecological perspectives because it is responsible both for generating the vast majority of hydrogen used to fix carbon into the earth's biosphere and for releasing oxygen necessary for respiration. The understanding of this process takes on added importance given the recognition of anthropomorphic changes such as global warming and ozone depletion because PSII is potentially quite sensitive to these environmental stresses. The project is basic research into the enzyme mechanism of PSII and because PSII is also a membrane protein, the knowledge gained from this project should also positively impact the field of membrane biology, which has many important applications.

这个项目的重点是光合作用水氧化反应催化位点的结构和组装。这项工作结合了分子遗传学、生物化学和生物物理学的方法来阐明光活化的过程，这是形成水氧化复合物核心的锰原子催化四聚体的顺序光依赖性组装。光活化是金属蛋白组装过程中一个令人着迷的问题。这是一个多量子过程，涉及一系列动力学可分解的分子重排，通过锰的光氧化和钙的结合来稳定。在这一过程中发生的分子事件尚不清楚，本研究的主要目的是根据在组装序列中为进入的锰离子和钙离子提供配位环境的蛋白质基团的影响来定义这些事件。该研究是由许多部分受损的锰和钙配体在复杂的内在部分和外源多肽突变的位点导向突变的可用性，这已被证明可以调节组装过程的效率。利用极谱法和荧光法监测组装过程。早期使用完整突变蓝藻细胞的光激活研究现在扩展到体外研究，在体外研究中，可以更详细地分析正常和转基因反应中心核心复合物的辅因子需求。光合作用是一个全球性的重要过程，有许多尚未解决的关键特征。光合作用机制中最令人困惑的方面是PSII水分解酶的氧气生产。从农业和生态的角度来看，PSII都是至关重要的，因为它既负责产生用于将碳固定在地球生物圈中的绝大多数氢，又负责释放呼吸所需的氧气。考虑到全球变暖和臭氧消耗等拟人化变化的认识，对这一过程的理解变得更加重要，因为PSII对这些环境压力可能相当敏感。该项目是对PSII酶机制的基础研究，由于PSII也是一种膜蛋白，因此该项目所获得的知识也将对膜生物学领域产生积极的影响，具有许多重要的应用价值。