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项目共同支持，目的是了解控制蛋白质中电子转移反应速率的低频正常振动模式的结构本质。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事件，因为这些模式解释了定义反应坐标的反应物分子的限速结构重排。尽管它们很重要，但对于哪些结构在运动，以及正常振动模式中涉及的运动特征，我们所知甚少。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良好候选模式。像这样的相互作用允许蛋白质调整嵌入的发色团的电子特性和反应性。这些模式可以用一种飞秒时域形式的共振拉曼光谱被称为动态吸收光谱来检测。本项目利用了本实验室在检测和分析溶液和蛋白质宿主中电子发色团的基态和激发态势能表面上低频相干波包运动产生的信号方面的最新进展。这项工作的一个重要发现是，具有离域pi电子系统的发色团的第一溶剂化壳中的聚集溶剂分子可以与发色团的pi到pi*电子跃迁进行振动耦合；它们通过攻击发色团的pi电子密度获得共振拉曼活性。研究的最初重点将是表征锌（II）取代卟啉在溶液和两种简单蛋白质宿主细胞色素c和肌红蛋白中的振动相干性。这些研究的重点将放在邻溶剂或氨基酸侧链与卟啉pi电子密度的有序极性和非极性分子间相互作用上。本项目将发展的方法和思想在生物系统、材料和凝聚相的化学动力学研究中具有广泛的应用潜力。在蛋白质和溶剂动力学的时间分辨光谱研究中使用强电子发色团对蛋白质稳定性和折叠/错误折叠领域也具有潜在的重要性。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，提供关键的讲座主题和应用，甚至在入门课程中。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.