Primary Electron Transfer Processes in Photosynthetic Bacterial Reaction Centers

光合细菌反应中心的初级电子转移过程

• 批准号: 0614529
• 负责人: Dewey Holten
• 金额: --
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-03-01 至 2010-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0614529&HistoricalAwards=false
• 关键词: Primary; Electron; Transfer; Processes; Photosynthetic

The ultimate goal of this research is to achieve a unified molecular level understanding of the photochemical processes in the bacterial photosynthetic reaction center (RC). The RCs of both bacteria and plants feature two quasi-symmetric branches of potential electron carriers. In the bacterial RC, only the L-branch (also called the A branch) is utilized for trans-membrane photo-induced electron transport. In the native RC, the M-branch (also called the B branch) is inactive. Recent work from this project has delineated conditions wherein the M-branch cofactors can be induced to support full trans-membrane electron transfer, albeit in low yield. This advance has opened the door for detailed explorations of the origins of the unidirectional electron transfer in the native RC, and of electron transfer along the entire normally inactive M-branch of RC cofactors. Such studies are the basis of this research. This work will put current models for the high quantum yield of charge separation along the L-side in the native RC to the ultimate test of consistency via manipulation and study of the same processes along the normally inactive M branch. The findings will help to elucidate the mechanistic underpinnings of electron transfer in the RC as a unified whole. From a wider perspective, the proposed work will make the normally inactive M-side cofactor chain fully accessible in a robust manner for a variety of next-generation studies in many laboratories. This includes new avenues for exploring novel intermediates and conformational or protonation states associated with the QA/QB two-electron gate function that are normally not produced or formed only transiently in the normal course of L-side charge separation. One goal will be to manipulate the cofactor content and the free energies of both the L and M-side charge-separated states to give a very high (approaching quantitative) yield of electron transfer to the normally inactive M-branch. A second goal will be to probe the contribution of electronic couplings along with energetics to directionality (i.e., initial L-side versus B-side charge separation). A third goal will be to increase the rate and yield of electron transfer from the M-side bacteriopheophytin intermediary electron acceptor to the terminal quinone acceptor QB, and in doing so test current understanding of the analogous L side processes. These goals will be pursued via static and time-resolved (femtoseconds to seconds) spectroscopic studies of RC mutants to derive the rates and yields of the charge separation and recombination processes and the relative free energies of the participating states. This research is central to understanding the primary photochemical events in the bacterial RC, and will continue to provide guideposts for research being conducted on photosystems I and II from green plants. Broader Impacts:This research will continue to have a demonstrated impact in the participation of undergraduates and underrepresented groups in research and science, and in the broad multidisciplinary training the researchers receive. The integration of research ideas into teaching and educational development will continue to be a focus of the Co-PIs, via three projects. (1) A web-based tutorial will be developed that can 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 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 application-oriented perspectives. (3) A broad, science-based lecture on general and fundamental aspects of photosynthesis with links to interests in gardening will be developed to be part of an adult education outreach program at the Missouri Botanical Garden. Despite the undeniable relevance of photosynthesis, the program has not had such a lecture/education component. Finally, in addition to the traditional means of dissemination (publications, meetings), local and national popular print and web-based publication venues will continue to be exploited through contacts with science writers in order to disseminate photosynthesis research (and contributions made under this project) to a broad spectrum of individuals.

本研究的最终目的是在分子水平上对细菌光合反应中心（RC）的光化学过程有一个统一的认识。细菌和植物的RC都具有两个准对称的潜在电子载体分支。在细菌RC中，仅L-分支（也称为A分支）用于跨膜光诱导的电子传递。在天然RC中，M分支（也称为B分支）是不活动的。该项目的最新工作已经描绘了其中M分支辅因子可以被诱导以支持完全跨膜电子转移的条件，尽管产量较低。这一进展打开了大门，详细探索的起源，单向电子转移在本机RC，电子转移沿着整个正常情况下不活跃的M-分支RC辅因子。这些研究是本研究的基础。这项工作将把目前的模型的高量子产率的电荷分离沿着的L-侧在本地RC的最终测试的一致性，通过操纵和研究相同的过程沿着通常不活跃的M分支。研究结果将有助于阐明电子转移的RC作为一个统一的整体的机制基础。从更广泛的角度来看，拟议的工作将使通常无活性的M侧辅因子链以稳健的方式完全可用于许多实验室的各种下一代研究。这包括新的途径，探索新的中间体和构象或质子化状态与QA/QB双电子门功能，通常不会产生或只形成短暂的L侧电荷分离的正常过程中。一个目标将是操纵辅因子含量和L和M侧电荷分离态的自由能，以给出非常高的（接近定量）电子转移到通常无活性的M分支的产率。第二个目标将是探测电子耦合沿着能量学对方向性的贡献（即，初始L侧对B侧电荷分离）。第三个目标将是增加从M侧细菌脱镁叶绿素中间电子受体到末端醌受体QB的电子转移的速率和产率，并且在这样做时测试目前对类似L侧过程的理解。这些目标将追求通过静态和时间分辨（飞秒至秒）的光谱研究RC突变体的电荷分离和重组过程的速率和产量和参与状态的相对自由能。这项研究是中央的了解在细菌RC的主要光化学事件，并将继续提供路标的研究正在进行的光系统I和II从绿色植物。更广泛的影响：这项研究将继续对本科生和代表性不足的群体参与研究和科学以及研究人员接受的广泛的多学科培训产生明显的影响。通过三个项目，将研究思想融入教学和教育发展将继续成为Co-PI的重点。(1)将为本科生或高中生量身定制一个关于“为什么草是绿色而血红色？“（2）两项本科生物理化学实验将大幅提升，以探讨叶绿素和相关发色团的光谱学，以及光合作用的关键能量/电子转移过程，从应用的角度教授分子电子光谱学和动力学。(3)将在密苏里州植物园开发一个广泛的、以科学为基础的关于光合作用的一般和基本方面的讲座，并将其与园艺兴趣联系起来，作为成人教育推广计划的一部分。尽管光合作用不可否认的相关性，该计划还没有这样的讲座/教育组成部分。最后，除了传统的传播手段（出版物、会议）外，将继续通过与科学作家的联系，利用地方和国家大众印刷品和网络出版物，向广大个人传播光合作用研究（以及在本项目下作出的贡献）。