Resonance Raman Activity From Protein- and Solvent-Derived Modes in Charge-Transfer Proteins

该项目由分子和细胞生物科学部的分子生物物理学和化学部的实验物理化学计划共同支持，旨在了解控制蛋白质电子转移反应速率的低频正常振动模式的结构性质。蛋白质中的低频振动模式对各种生物过程的动力学具有重要意义，包括视觉和光合作用的第一个事件，因为这些模式解释了反应物分子的限速结构重排，定义了反应坐标。尽管它们的重要性，很少有人具体知道哪些结构正在移动，也没有了解正常振动模式中所涉及的运动特征。PI实验室最近的工作表明，电子发色团与周围蛋白质或溶剂之间的分子间模式是控制蛋白质中电子转移反应的模式的良好候选者。像这样的相互作用允许蛋白质调整嵌入发色团的电子性质和反应性。 这些模式可以使用称为动态吸收光谱的飞秒时域形式的共振拉曼光谱来检测。该项目利用了该实验室在探测和分析溶液和蛋白质宿主中电子发色团的地面和激发态势能表面上低频相干波包运动所产生的信号方面取得的最新进展。这项工作的一个重要发现是，在第一溶剂化壳层的发色团与离域π电子系统的簇溶剂分子可以振动耦合到发色团的π到π * 电子跃迁，他们获得共振拉曼活性攻击的π电子密度的发色团。最初的研究重点将是锌（II）取代的卟啉在溶液中的振动相干性的表征和两个简单的蛋白质主机，细胞色素c和肌红蛋白。这些研究的重点将是相邻溶剂或氨基酸侧链与卟啉π电子密度的有序极性和非极性分子间相互作用，本项目将开发的方法和思想在生物系统、材料和凝聚相中的化学动力学研究中具有广泛的应用前景。强电子生色团的使用在蛋白质和溶剂动力学的时间分辨光谱研究也是潜在的重要性，蛋白质的稳定性和折叠/错误折叠的区域。这项研究将在PI的研究生和本科教学中发挥不可或缺的作用，提供关键的演讲主题和应用，即使在入门课程。此外，这项工作将为各级研究生提供良好的培训。这项工作将使学生接触到广泛的学科，从结构生物学到化学物理学。

The objective of this project, jointly supported by Molecular Biophysics in the Division of Molecular and Cellular Biosciences and the Experimental Physical Chemistry Program in the Chemistry Division, is to understand the structural nature of the low-frequency normal modes of vibration that control the rate of electron-transfer reactions in proteins. Low-frequency vibrational modes in proteins are of significance to the dynamics of a variety of biological processes, including those of the first events of vision and photosynthesis, because these modes account for the rate-limiting structural rearrangement of the reactant molecules that defines the reaction coordinate. Despite their importance, very little is concretely known about which structures are moving nor is the character of the motion involved in the normal mode of vibration understood. Recent work in the PI's laboratory suggests that intermolecular modes between electronic chromophores and the surrounding protein or solvent are good candidates for the modes that control electron-transfer reactions in proteins. Interactions like these allow a protein to tune the electronic properties and reactivity of the imbedded chromophores. These modes can be detected using a femtosecond time-domain form of resonance Raman spectroscopy called dynamic absorption spectroscopy. This project takes advantage of recent progress made in this laboratory in the detection and analysis of signals arising from low-frequency coherent wave-packet motion on the ground and excited-state potential-energy surfaces of electronic chromophores in solution and in protein hosts. An important finding from this work is that clustered solvent molecules in the first solvation shell of chromophores with delocalized pi-electron systems can be vibronically coupled to the chromophore's pi-to-pi* electronic transition; they obtain resonance Raman activity by attacking the pi-electron density of the chromophore. The initial focus of the research will be on characterization of vibrational coherence of Zn(II)-substituted porphyrins in solution and in two simple protein hosts, cytochrome c and myoglobin. The focus in these studies will be on the ordered polar and non-polar intermolecular interactions of neighboring solvent or amino acid side chains with the pi-electron density of the porphyrin.The methods and ideas that will be developed in this project are potentially of broad use in the study of chemical dynamics in biological systems, materials, and in condensed phases. The use of strong electronic chromophores in time-resolved spectroscopic studies of protein and solvent dynamics is also of potential importance to the area of protein stability and folding/misfolding. This research will play an integral role in the PI's graduate and undergraduate teaching by providing key lecture topics and applications even in introductory courses. Additionally, the work will provide excellent training for research students at all levels. The work will expose the students to a wide range of disciplines, ranging from structural biology to chemical physics.