Microscopic Dielectric Relaxation as a Tool for Studying Protein Dynamics

蛋白质结构域的集体运动通常发生在纳秒或皮秒的时间尺度上，对蛋白质的功能至关重要。色氨酸残基的时间分辨和光谱分辨荧光发射包含关于这些时间尺度上的蛋白质弛豫动力学的信息。这种类型的动态信息是对从X射线衍射和核磁共振数据获得的结构和动态信息的补充。用短激光脉冲激发色氨酸残基会改变它和带电残基之间的静电力，使系统失去平衡。当系统弛豫到一个新的平衡时，色氨酸发射光谱向更低的能量移动，这种移动可以用皮秒的时间分辨率来记录。初步研究表明，少数被测蛋白质的驰豫曲线包含三个或三个以上的指数项，其驰豫时间在60ps到8 ns之间不同。较快的指数表示小化学基团的运动，而较慢的指数表示大块结构域或二级结构元素的相对运动。本研究的目的是在由荧光数据得到的实验弛豫曲线与理论之间建立定量的对应关系。通过改变色氨酸残基和带电残基的位置，研究不同类型振动的动力学。这项技术将被用来将域内运动与不同域间的相对运动分开。第二部分的工作将集中在与单个电荷的添加和移除相关的松弛曲线的变化。所提出的活动的智力优势在于关于蛋白质集体运动的皮秒和纳秒动力学的新信息。除了培养研究生，PI还将在他的实验室培训本科生和高中生。这些学生的目的是向他们传授科学研究的兴奋，并向他们展示他们在生物物理学领域有什么职业选择。

Collective motion of protein domains usually takes place on the nanosecond or picosecond time scales and is important for protein function. Time- and spectrally-resolved fluorescence emission of tryptophan residues contains information about protein relaxation dynamics on these time scales. This type of dynamic information is complementary to the structural and dynamic information available from X-ray diffraction and NMR data. Exciting a Trp residue with a short laser pulse alters the electrostatic forces acting between it and charged residues and throws the system out of equilibrium. As the system relaxes to a new equilibrium, the Trp emission spectrum shifts to lower energies, and this shift can be recorded with picosecond time resolution. Preliminary studies revealed that the relaxation curves for a few tested proteins contain three or more exponential terms with different relaxation times in the range from 60ps to 8ns. The faster exponentials represent the motion of small chemical groups, while the slower exponentials represent the relative motions of bulky domains or secondary-structure elements. The goal of this research is to establish quantitative correspondence between the experimental relaxation curves obtained from fluorescence data and theory. By changing the location of the Trp residue and of charged residues, the dynamics of different kinds of vibrations will be studied. This technique will be used to separate intradomain motions from the relative motions of different domains. The second part of the work will focus on changes in the relaxation curves associated with the addition and removal of a single charge.The intellectual merit of the proposed activity is in the new information about picosecond and nanosecond dynamics of collective motions in proteins. In addition to training graduate students, the PI will train undergraduate and high school students in his laboratory. The aim with these students is to impart the excitement of scientific research to them and to show them what career options are available to them in Biophysics.