Protein Control of Electron Transfer Pathways in Photosynthesis

光合作用中最初的太阳能保存事件是在反应中心的一个激发的供体分子和邻近的受体分子之间的电子转移，这是一个固有的膜蛋白-色素复合物。在这个项目中，PI将继续他对紫色非硫细菌球形红杆菌的研究，研究初始电子转移反应的驱动力和温度依赖性。PI使用了反应扩散理论的一种形式，以前应用于粘性溶剂中的电子转移，描述了电子转移的复杂动力学，作为驱动力和温度的函数。这种方法已经非常成功，这意味着由光吸收引起的蛋白质构象变化控制了观察到的动力学，而不是两个潜在表面之间的静态屏障交叉。这项工作提出了几个需要回答的重要问题。首先，蛋白质运动的性质和280纳米的光谱信号似乎是这种运动的探针是不清楚的。目前的假设是，这是由于色氨酸残基对蛋白质环境变化的反应，但这仍有待证实。其次，有必要对蛋白质弛豫和电子转移之间的关系进行更详细的机制探索。这个新模型提供了一个机会来确定重组能量、驱动力和整个突变体的耦合作为温度的函数，从而产生一个比以前可用的更完整的初始光合电子转移的机制图。最后，这项工作将与当前的定向进化方法相结合，以产生沿通常未使用的辅因子途径（b侧）进行高产量电子转移的突变体。然后将对这些突变体进行一组非常相似的研究，作为驱动力和温度的函数，以探索两种电子转移途径之间的机制相似性和差异性。PI参与扩大研究生和本科生水平的跨学科研究。PI有七名本科生与他一起工作，其中两人直接参与这个项目。此外，光合作用研究的概念也被用来丰富他在物理化学和生物化学方面的教学。例如，作为亚利桑那州立大学学习社区项目的一部分，PI教授一门关于生物纳米技术的课程，在该项目中，大二学生将探索纳米技术的科学、政策和社会学。PI也是NSF生物分子纳米技术研究项目的负责人。光合作用反应中心是纳米级光电器件的首要例子，这项工作的概念是IGERT学生研究的生物分子纳米技术的关键例子之一。PI也是亚利桑那州立大学生物能源研究计划的现任主任，这是亚利桑那州立大学光合作用中心的一个新计划，旨在利用我们对光合作用过程的日益了解，并将其用于开发新能源和能量转导手段。最后，PI指导生物设计研究所的生物光学纳米技术中心。在这个职位上，他直接与大量的私人、商业和公民团体打交道，这些讨论构成了社区嵌入式研究新方法的基础，在这种方法中，社会需求和发现过程被整合到跨学科研究的新混合模型中。该项目由生物科学理事会分子与细胞生物科学部的分子生物物理学和数学与物理科学理事会化学部的实验物理化学项目共同支持。

The initial solar energy conserving event in photosynthesis is the transfer of an electron between an excited donor and a neighboring acceptor molecule in the reaction center, an intrinsic membrane protein-pigment complex. In this project the PI will continue his studies of the purple nonsulfur bacterium Rhodobacter sphaeroides, investigating the driving force and temperature dependence of the initial electron transfer reactions. The PI has used a form of reaction diffusion theory, applied previously to electron transfer in viscous solvents, to describe the complex kinetics of electron transfer as a function of driving force and temperature. This approach has been remarkably successful, implying that protein conformational changes initiated by light absorption control the observed kinetics instead of a static barrier crossing between two potential surfaces. Several important questions have been raised by this work that need to be answered. First, the nature of the protein motion and the spectroscopic signal at 280 nm that appears to be a probe of this motion are unclear. It is currently hypothesized that this is due to tryptophan residues responding to changes in the protein environment, but this remains to be proven. Second, a more detailed mechanistic exploration of the relationship between protein relaxation and electron transfer is necessary. This new model provides an opportunity to determine the reorganization energy, driving force and coupling for a whole series of mutants as a function of temperature, resulting in a much more complete mechanistic picture of initial photosynthetic electron transfer than has ever been available previously. Finally, this work will be merged with current directed evolution approaches to produce mutants that undergo high yield electron transfer along the normally unused cofactor pathway (the B-side). A very similar set of studies as a function of driving force and temperature will then be performed on these mutants to explore the mechanistic similarities and differences between the two electron transfer pathways. The PI is involved in expanding interdisciplinary research at both the graduate and undergraduate levels. The PI has seven undergraduates working with him, two directly on this project. In addition, the concepts involved in photosynthetic research are used to enrich his teaching in both physical chemistry and biochemistry. For example, the PI teaches a course on bio-nanotechnology as part of a learning community project at ASU in which sophomores explore the science, policy and sociology of nanotechnology. The PI is also the director of an NSF IGERT program in biomolecular nanotechnology. The photosynthetic reaction center is a premier example of an optoelectronic device at the nanoscale and the concepts from this work are one of the key examples of biomolecular nanotechnology studied by the IGERT students. The PI is also the current director of the ASU BioEnergy Research Initiative, a new initiative growing out of ASU's Photosynthesis Center that seeks to take our growing understanding of photosynthetic processes and utilize them in the development of new energy sources and means of energy transduction. Finally, the PI directs the Center for BioOptical Nanotechnology in the Biodesign Institute. In this role, he directly interfaces with a large number of private, commercial and citizens groups, and these discussions form the basis for a new approach to community-embedded research, in which the needs of society and the process of discovery are integrated in a new hybrid model for interdisciplinary research. This project is jointly supported by Molecular Biophysics in the Division of Molecular and Cellular Biosciences in the Directorate for Biological Sciences and the Experimental Physical Chemistry Program in the Division of Chemistry in the Mathematical and Physical Sciences Directorate.