Assembly and Function of the Cyanobacterial Photosystem II Complex

在植物、藻类和蓝藻中发现的光系统II （PSII）复合体是一种叶绿素-蛋白质复合体，位于称为类囊体的特殊细胞膜内。PSII催化关键的水分解反应，利用太阳能产生地球生物圈中食物和能源生产所需的活性氢。与此同时，PSII负责地球上所有气态氧气的生产。尽管具有全球重要性，但PSII也可以被认为是光合生物的“阿喀琉斯之踵”。这是因为它很容易受到作为能量来源的光的伤害。因此，由于这种持续的光损伤，PSII处于持续的修复状态。该项目将阐明尚不清楚的修复机制，重点是氧演化所需的催化金属的组装。除了基础研究外，该项目还将为本科生和研究生在生物化学、生物物理学和分子遗传学领域提供广泛的培训机会。此外，这是该项目的一个大型外联组成部分，旨在为职前和在职高中教师提供研究机会。该项目将研究PSII水分解配合物的金属团簇（Mn4CaO5）催化中心的多步组装。最近的研究揭示了受损的PSII迁移到位于细胞外周区域的专门“修复区”。该项目验证了以下假设：(1)Mn4CaO5的丢失触发了向修复区迁移；(2)只有当受损的PSII复合体迁移到这些修复区后，Mn4CaO5簇的组装才能有效地进行。因为光也可以驱动Mn4CaO5的组装，所以这个过程可以用闪光来精确控制，这将使人们对蛋白质中金属簇组装的广泛问题有新的认识。这项工作将使用一种基因可转化的蓝藻和一系列技术，以分子分辨率探测组装过程。PI和合作者正在开发和利用最先进的生物物理和分子遗传技术。这些技术包括合成DNA、高速极谱、EPR和FTIR技术。

The photosystem II (PSII) complex found in plants, algae, and cyanobacteria is a chlorophyll-protein complex located in specialized internal cell membranes called thylakoids. PSII catalyzes the crucial water-splitting reaction that uses solar energy to produce the activated hydrogen required for food and energy production throughout the Earth's biosphere. At the same time, the PSII is responsible for the production of essentially all the gaseous oxygen on Earth. Despite its global importance, PSII can also be considered the "Achilles Heel" of photosynthetic organisms. This is because it is prone to damage from the very light that it uses as an energy source. Consequently, PSII is under a constant state of repair owing to this incessant light damage. The project will elucidate the poorly understood repair mechanism with a focus on the assembly of the catalytic metals necessary for oxygen evolution. In addition to the fundamental research, the project will provide extensive training opportunities for undergraduate and graduate students in in the areas of biochemistry, biophysics, and molecular genetics. Moreover, the is a large outreach component of the project that is designed to provide research opportunities for pre-service and in-service high school teachers. The project will investigate the multistep assembly of the metal cluster (Mn4CaO5) catalytic center of the PSII water-splitting complex. Recent work has revealed the migration of damaged PSII to specialized "repair zones" located in the peripheral regions of the cell. The project tests the hypotheses that (1) loss of the the Mn4CaO5 triggers the migration to repair zones and (2) the assembly of the Mn4CaO5 cluster occurs efficiently only after migration of the damaged PSII complex to these repair zones. Because light also drives Mn4CaO5 assembly, the process can be precisely controlled using flashes of light, which will allow new insights into the broad problem of metal cluster assembly in proteins. The work will use a genetically transformable cyanobacterium and an array of techniques that probe the assembly process with molecular resolution. State-of-the-art biophysical and molecular genetic techniques are being developed and utilized by the PI and collaborators. These include synthetic DNA, high-speed polarography, EPR, and FTIR techniques.