Primary Electron Transfer Processes in Photosynthetic Bacterial Reaction Centers

这项研究的最终目标是在分子水平上统一理解细菌光合作用反应中心的光化学过程，细菌光合作用反应中心是在光合作用细菌中发现的一种色素-蛋白质复合体。植物也有类似的光合作用机制。所有这些反应中心都有两个准对称的势载流子分支。在细菌反应中心，只有一个分支，即所谓的A分支，被用来储存(太阳)光的能量--通过跨膜光致A分支上的电子传递来完成。在天然反应中心，B分支是不活跃的。该项目的前期工作表明，在某些独特的条件下，可以诱导B-支链辅助因子来支持完全的跨膜电子转移。产率足够高，现在可以详细地探索沿着反应中心辅因子的整个正常不活跃的B分支的电子转移。这些研究是该项目的基础。本研究将测试当前的模型，并利用以前对活动分支(A分支)过程的研究获得的见解，并在此过程中阐明RC作为一个统一的整体中电子转移的机制基础。从更全球化的角度来看，这个项目的目的是使通常不活跃的B-分支辅因子链以一种稳健的方式完全可用于各种下一代研究。这项工作将为探索电子和/或构象变化、质子运动和其他类似过程开辟新的途径，这些过程被认为是与反应中心两个醌(Qs)的QA/QB双电子门功能有关的重要功能。这些目标将通过对具有多个氨基酸变化的RC突变体的静态和时间分辨(飞秒到秒)光谱研究来实现，这些研究合理地操纵辅因子的属性以及电荷分离和复合过程的速率和产量。这项研究不仅是理解细菌RC中主要光化学事件的核心，而且将为正在进行的植物光系统I和II的研究提供指南：了解光合作用RC中过程的分子水平机制为太阳能收集/转换的合成系统奠定基础，从而满足国家对下一代可再生能源的需求。本科生和研究生将参与这项研究。将研究理念融入教学和教育发展将重点放在两个项目上。(1)将开发基于网络的教程。它将为本科生或高中生量身定做，主题为“为什么草是绿的，血是红的？”(2)华盛顿大学的两个本科生物理化学实验室实验将进行广泛的升级，以利用叶绿素和相关生色团的光谱以及光合作用的关键能量/电子转移过程，从新的、面向应用的角度教授分子电子光谱和动力学。最后，密苏里州植物园成人教育推广计划的一部分，将开发一场广泛的、以科学为基础的讲座，内容涉及光合作用的一般和基本方面，并与园艺兴趣相联系。尽管光合作用具有不可否认的相关性，但该计划目前还没有这样的讲座/教育部分。通过这些方式，我们将努力向更广泛的个人传播对光合作用及其与地球栖息地的关系的理解，以及对太阳能研究的理解。

The ultimate goal of this research is to achieve a unified molecular level understanding of the photochemical processes in the bacterial photosynthetic reaction center, which is a pigment-protein complex found in photosynthetic bacteria. Plants have similar photosynthetic machinery. All these reaction centers have in common two quasi-symmetric branches of potential electron carriers. In the bacterial reaction center, only one of them, the so-called A-branch, is utilized for storing the energy of (sun)light -accomplished by trans-membrane photo-induced electron transport on the A branch. In the native reaction center, the B-branch is inactive. The previous work in this project has shown that under certain unique conditions, the B-branch cofactors can be induced to support full trans-membrane electron transfer. The yield is high enough that detailed explorations of electron transfer along the entire normally inactive B-branch of reaction center cofactors are now possible. Such studies are the basis of this project. This research will test current models and exploit insights gained from previous studies of the active-branch (A-branch) processes and in doing so elucidate mechanistic underpinnings of electron transfer in the RC as a unified whole. From a more global perspective, this project is aimed at making the normally inactive B-branch cofactor chain fully accessible in a robust manner for a variety of next-generation studies. This work will open up new avenues for exploring electronic and/or conformational changes, proton movement and other similar processes that are thought to be functionally significant in association with the QA/QB two-electron gate function of the two quinones (Qs) in the reaction center. These goals will be pursued via static and time-resolved (femtoseconds to seconds) spectroscopic studies of RC mutants with multiple amino acid changes that rationally manipulate the properties of the cofactors and the rates and yields of the charge separation and recombination processes. This research is not only central to understanding the primary photochemical events in the bacterial RC, but also will provide guideposts for research being conducted on plant photosystems I and II.Broader Impact: Understanding the molecular-level mechanisms of the processes in the photosynthetic RC lays a foundation for synthetic systems for solar-energy harvesting/conversion, thereby addressing a national need for next generation renewable energy sources. Undergraduate and graduate students will participate in this research. The integration of research ideas into teaching and educational development will focus on two projects. (1) A web-based tutorial will be developed. It will be tailored for undergraduate or high school students, on the general topic "Why is grass green and blood red?" (2) Two undergraduate physical-chemistry laboratory experiments at Washington University will be extensively upgraded to exploit the spectroscopy of chlorophyll and related chromophores, and the energy/electron transfer processes critical to photosynthesis, to teach molecular electronic spectroscopy and kinetics from new, application-oriented perspectives. Finally, a broad, science-based lecture on general and fundamental aspects of photosynthesis with links to interests in gardening will be developed as a proposed part of an adult education outreach program at the Missouri Botanical Garden. Despite the undeniable relevance of photosynthesis, the program does not have such a lecture/education component at present. In these ways we will endeavor to disseminate an understanding of photosynthesis, its relation to the earth's habitat, and to solar energy research to a broad spectrum of individuals.