Primary Electron Transfer Processes in Photosynthetic Bacterial Reaction Centers

本研究的最终目标是实现对细菌光合反应中心光化学过程的统一分子水平认识，该中心是光合细菌中发现的一种色素-蛋白质复合物。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潜在电子载流子分支。在细菌反应中心，只有其中一个，即所谓的A支，被用来储存（太阳）光的能量，这是通过A支上的跨膜光诱导电子传递来完成的。在天然反应中心，b支是无活性的。本项目前期的工作表明，在某些特殊条件下，b支辅因子可以被诱导支持完全的跨膜电子转移。产率足够高，现在可以沿着整个通常不活跃的反应中心辅助因子的b支详细探索电子转移。这些研究是本项目的基础。这项研究将测试当前的模型，并利用从以前的有源分支（a -分支）过程研究中获得的见解，并以此阐明RC中作为一个统一整体的电子转移的机制基础。从更全局的角度来看，该项目旨在使通常不活跃的b支辅因子链以健壮的方式完全可访问，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，这些过程被认为与反应中心两个醌（Qs）的QA/QB双电子门功能有重要的功能关联。这些目标将通过对RC突变体的静态和时间分辨（飞秒到秒）光谱研究来实现，这些突变体具有多种氨基酸变化，可以合理地操纵辅因子的性质以及电荷分离和重组过程的速率和产率。这项研究不仅对理解细菌RC的主要光化学事件至关重要，而且将为植物光系统I和II的研究提供指导。更广泛的影响：了解光合作用RC过程的分子水平机制为太阳能收集/转换的合成系统奠定了基础，从而解决了国家对下一代可再生能源的需求。本科生和研究生将参与本研究。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)开发网络教程。它将为本科生或高中生量身定制，主题是“为什么草是绿的，血是红的？”(2)华盛顿大学的两个本科物理化学实验室实验将广泛升级，以利用叶绿素和相关发色团的光谱学，以及光合作用关键的能量/电子转移过程，从新的面向应用的角度教授分子电子光谱学和动力学。最后，一个广泛的，以科学为基础的讲座，关于光合作用的一般和基本方面，并与园艺兴趣联系起来，将作为密苏里植物园成人教育推广计划的一部分。尽管光合作用具有不可否认的相关性，但该项目目前还没有这样的讲座/教育组成部分。通过这些方式，我们将努力传播对光合作用的理解，它与地球栖息地的关系，以及对广泛的个人的太阳能研究。

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.