Protein Dynamics in Electron Transfer

本项目将分子动力学模拟和实验测量相结合，建立了紫色非硫细菌球形红细菌反应中心光合作用电子传递的动力学模型。目前对该系统的模拟表明，慢速、集体蛋白质模式参与调节这些反应是关键，因此，反应过程中可用的重组能量的量在很大程度上取决于反应的时间尺度，特别是当一个人从皮秒移动到纳秒时。在这里，一个理论小组和一个实验小组联手探索蛋白质动力学是如何参与平衡两个相互竞争的电子转移反应的，这两个反应对光合作用中的太阳能转换至关重要。第一种是发生在200ps时标上的从细菌素中间体到苯二酚的有效电子转移反应。第二种是竞争的非生产性复合反应，在该反应中，电子在10-20 ns的时间尺度上返回给电子体。模拟和测量将作为这两个反应的驱动力和温度的函数进行，并直接进行比较，目的是了解大自然如何优化蛋白质结构和动力学，以促进生产性光合作用功能。将研究一系列表面电荷突变体和不同的pH，以检验模拟所建议的蛋白质/水界面上的电荷分布控制初始和末态势面形状的概念。此外，被认为会改变潜在表面之间位移的内部突变也将被研究。最终目标是提供从蛋白质结构定量预测这一复杂生物系统中的生化反应动力学和相关功能的能力。开发一种定量的、基于结构的光合作用反应中心结构、动力学和功能之间关系的模型将具有广泛的价值。在这方面，反应中心代表着某种具有高分辨率结构数据和用于相当详细地监测电子转移的固有光学探测器的“分子实验室”。该项目将支持梅萨高中生物技术学院的学生在基因操作和光合细菌光谱探测的基础上开发完整的参与式学习体验。这将包括在一个夏天在亚利桑那州立大学的实验室进行教师培训，然后PI直接与学院的教师和学生合作，在接下来的几年里开展这项活动。在过去的5年里，PI在实验室里有25名本科生，他们非常积极地参与了本科生的指导工作。

This project integrates molecular dynamic simulation and experimental measurement to develop a dynamic model for photosynthetic electron transfer in reaction centers of the purple nonsulfur bacterium, Rhodobacter sphaeroides. Current simulations on this system have suggested that the involvement of slow, collective protein modes in mediating these reactions is key, and as a result, the amount of reorganization energy available during a reaction is profoundly dependant on the time scale of the reaction, particularly as one moves from picoseconds to nanoseconds. Here, a theoretical group and an experimental group have joined forces to explore how proteins dynamics is involved to balance two competing electron transfer reactions that are critical to solar energy conversion in photosynthesis. The first is a productive electron transfer reaction that takes place on the 200 ps timescale from a bacteriopheophytin intermediate to a quinone. The second is the competing unproductive recombination reaction in which the electron returns back to the original electron donor on the 10-20 ns time scale. Simulations and measurements will be performed as a function of the driving force and temperature for these two reactions and compared directly, the goal being to understand how Nature has optimized protein structure and dynamics to promote productive photosynthetic function. A series of surface charge mutants and different pH's will be investigated, testing the concept that that the charge distribution at the protein/water interface controls the shape of the initial and final state potential surfaces, as suggested by simulation. In addition, internal mutations, thought to alter the displacement between potential surfaces, will also be investigated. The ultimate objective is to provide the capability to quantitatively predict biochemical reaction dynamics and associated function from protein structure in this complex biological system. The development of a quantitative, structure-based model of the relationship between structure, dynamics and function in the photosynthetic reaction center would be broadly valuable. The reaction center in this respect represents something of a "lab on a molecule" with high resolution structural data and the inherent optical probes for monitoring electron transfer in considerable detail. The project will support the development of a complete, participatory learning experience for the students in the Mesa High School Biotechnology Academy, based on genetic manipulation and spectroscopic probing of photosynthetic bacteria. This will involve both teacher training in the ASU laboratories during one summer and then PIs working directly with the teachers and students in the academy to perform the activity during the subsequent years. The PIs are very heavily involved in undergraduate mentoring having had 25 undergraduates in the lab during the last 5 years.