CAREER: Understanding the Role of Amino Acid Radicals in Electron Transfer

氨基酸自由基对许多基本生物过程的催化机制至关重要，包括核酸代谢、DNA修复、光合作用和有氧呼吸。在氧化过程中，氨基酸自由基可以作为正电荷的“汇”，通过多步隧道效应促进蛋白质中远距离（25埃）电子转移。然而，尽管氨基酸自由基在生物学上具有重要意义，但它们的电化学和电子转移性质尚未得到很好的定义。在这个项目中，这些特性将直接使用β -片蛋白azurin和4-螺旋束蛋白细胞色素c'作为模型系统进行测量。为了研究电化学电位对电子传递机制的影响，将非天然的Trp和Tyr氨基酸掺入多肽链的特定位点。与天然氨基酸相比，这扩大了电化学电位~ +/- 0.4 V的范围。此外，一些Tyr类似物的pKa值在生物pH范围内。这些提供了一个独特的机会，从动力学上分离电子转移从伴随的质子转移步骤，是强制性的生物电子转移。类似物还为确定局部氨基酸环境提供了独特的光谱处理。更广泛的影响：与拟议的研究相结合的是一个以研究为导向的高级生物化学课程的发展，该课程将讲座与实验室时间相结合。该课程的目标是让更多的本科生接触科学研究，并鼓励他们从事科学事业。课程评估和结果评估的指导方针也包括在内。该课程还为研究生或博士后学者提供了探索创新教学方法和展示课程材料所需的资源。我们特别努力招募美国本土的本科生和研究生来参与这个项目。与蒙大拿部落学院的现有联系极大地促进了这一点。

Amino acid radicals are vital to the catalytic mechanisms of many fundamental biological processes, including nucleic acid metabolism, DNA repair, photosynthesis, and aerobic respiration. Amino acid radicals may serve as "sinks" for positive charges during oxidation, to facilitate very long-range (25 angstrom) electron transfer in proteins via multi-step tunneling. Yet despite the significance of amino acid radicals in biology, their electrochemical and electron transfer properties are not well defined. In this project, these properties will be measured directly using the beta-sheet protein azurin and the 4-helix bundle protein cytochrome c' as model systems. To investigate the effects of electrochemical potentials on electron transfer mechanisms, non-natural Trp and Tyr amino acids will be incorporated at specific sites of the polypeptide chains. This extends the range of electrochemical potentials ~ +/- 0.4 V compared with the natural amino acids. Moreover, several Tyr analogs have pKa values within the biological pH range. These offer a unique opportunity to kinetically separate electron transfer from the accompanying proton transfer step that is obligatory in biological electron transfer. The analogs also provide distinctive spectroscopic handles for defining local amino acid environments.Broader impacts: Coupled with the proposed research is the development of a research-oriented upper level biochemistry course that integrates lectures into laboratory time. The goals of the course are to expose more undergraduates to scientific research and encourage them to pursue careers in science. Guidelines for course evaluation and outcomes assessment are also included. The course also provides a graduate student or postdoctoral scholar with the resources needed to explore innovative ways of teaching and presenting course material. Special efforts are made to recruit native American undergraduate and graduate students to work on the project. This is greatly facilitated by existing contacts with tribal colleges in Montana.