Electron Transfer Processes in Iron and Copper Proteins

描述(由申请人提供)：电子转移(ET)过程是活细胞中能量传递途径的重要元素。这项研究计划的总体目标是确定控制这些反应速度的因素。研究的重点是确定蛋白质结构如何调节电子流动；速率如何取决于氧化还原部位的能量；氧化还原部位的电子结构如何影响电子转移的方向性和效率；以及速率如何取决于蛋白质的构象和动力学。 目的1：当蛋白质中氧化还原位点之间的电子偶联较强，而多肽松弛动力学较慢时，理论认为ET率与偶联强度无关，并受多肽松弛动力学的限制。介质动力学的影响将通过研究强偶联Ru和Os修饰的蛋白质中的ET来探讨。 目的2：介导性多肽的三维结构决定了氧化还原中心之间的偶联效率。为了确定侧链原子在调节长程偶联中的重要性，将检查具有相似主干结构但不同一级序列的Ru修饰蛋白质中的ET率。 目的3：氨基酸自由基(如色氨酸、酪氨酸)被认为在蛋白质中起关键的酶作用的蛋白质越来越多。为了评估它们在酶催化中的作用，必须对Trp和Tyr氧化还原反应的动力学和机理有详细的了解。我们将研究Re和Ru修饰的天青中自由基形成和还原的动力学，以阐明质子和电子转移反应之间的相互作用。 目的4：为了不使ET在生物氧化还原过程中成为速率限制，需要毫秒或更快的隧道时间。对于较低的驱动力，这一要求将生物隧穿反应的最大施主-受体距离设置为大约20A。为了实现更长距离的电子传输，需要多个隧穿步骤。将设计和制备具有氧化还原活性基团(例如，3-硝基酪氨酸)的Ru修饰和重新修饰的天青素，以便在实验上测试多步隧道效应在调节长程电子传输方面的效率。

DESCRIPTION (provided by applicant): Electron-transfer (ET) processes are vital elements of energy transduction pathways in living cells. The broad goal of this research program is to define the factors that control the rates of these reactions. Research is focused on defining how protein structure regulates electron flow; how rates depend on the energetics of the redox sites; how the electronic structures of the redox sites affect the directionality and efficiency of electron transfer; and how rates depend on protein conformation and dynamics. Aim 1: When the electronic coupling between redox sites in a protein is strong, and polypeptide relaxation dynamics are slow, theory suggests that ET rates are independent of coupling strength and are limited by the polypeptide relaxation dynamics. The effects of medium dynamics will be probed with investigations of ET in strongly coupled Ru- and Os-modified proteins. Aim 2: The efficiency of the coupling between redox centers is determined by the three-dimensional structure of the intervening polypeptide. ET rates in Ru-modified proteins with similar backbone structures but different primary sequences will be examined in order to determine the importance of side-chain atoms in mediating long-range couplings. Aim 3: There is a rapidly growing list of proteins in which amino-acid radicals (e.g., tryptophan, tyrosine) are believed to play key enzymatic roles. In order to assess their roles in enzyme catalysis, a detailed understanding of the kinetics and mechanisms of Trp and Tyr redox reactions must be developed. The kinetics of radical formation and reduction in Re- and Ru-modified azurins will be investigated to elucidate the interplay between proton- and electron-transfer reactions. Aim 4: In order that ET not become rate-limiting in biological redox processes, millisecond or faster tunneling times are required. For low driving forces, this requirement sets the maximum donor-acceptor distance for biological tunneling reactions at approximately 20 A. Multiple tunneling steps are necessary to effect electron transport over longer distances. Ru- and Re-modified azurins with intervening redox-active groups (e.g., 3-nitrotyrosine) will be designed and prepared in order to test experimentally the efficiency of multistep tunneling in mediating long-range electron transport.