Phase-Sensitive Chiral Sum Frequency Generation Vibrational Spectroscopy for Probing Protein Hydration at Aqueous Interfaces

在化学系生命过程化学(CLP)项目的支持下，耶鲁大学的严翠英教授正在通过开发一种新的光学方法来研究蛋白质与表面水的相互作用。蛋白质是执行生物功能的分子机器。许多细胞存在于细胞表面，参与重要的生命过程，如细胞通讯、细胞黏附和免疫反应。这些蛋白质是药物设计的极佳靶点，最近成功开发出新冠肺炎疫苗就是一个例子。在工业中，蛋白质与表面相互作用时的稳定性会极大地影响产品质量，如食品包装和药物输送系统。此外，蛋白质被结合在表面上，用于制造生物传感器和分子器件。因此，能够预测蛋白质在不同表面上的行为有助于推进基础知识和开发新的药物和材料。尽管如此，表面的蛋白质不能自行发挥作用。它们不仅与表面材料(如细胞膜和塑料袋)相互作用，还与周围的水分子结合在一起。这些水分子决定了蛋白质的结构和功能，因此必须加以考虑才能充分理解和预测蛋白质的行为。严教授将开发一种新的光学技术，具有前所未有的选择性，用于检测水分子及其与表面蛋白质的相互作用。结合实验和计算方法，严教授将开发方法来生成这些水分子与表面各种类型的蛋白质相互作用的详细描述。严教授将为各级学生提供进行科学研究的培训机会，并组织学生接触邻里高中，支持他们的STEM教育计划，并就STEM就业机会进行小组讨论。该项目将开发外差手性振动和频率(SFG)产生光谱来探测界面上的蛋白质水合作用。该方法具有原位、实时、无标记等优点。更重要的是，它将为折叠手性结构的蛋白质周围的水分子提供独特的选择性，而不会受到来自界面水和主体水的背景信号的干扰。该项目将建造一台外差SFG光谱仪，在存在蛋白质的情况下获取空气/水界面的水O-H伸缩光谱，并注意其二级、三级和四级结构。在界面处构建的分子动力学(MD)模型将用于模拟相分辨的手性SFG光谱。将实验光谱和计算光谱的比较与MD轨迹的分析相结合，将允许提取有关蛋白质周围水分子的拓扑和局部相互作用的信息。最后，实验和计算相结合的方法将被用来研究蛋白质在表面变性过程中水结构的变化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemistry of Life Processes (CLP) Program in the Division of Chemistry, Professor Elsa Chui-Ying Yan of Yale University is studying protein interactions with water on surfaces by developing a new optical method. Proteins are molecular machineries that carry out biological functions. Many of them are situated on cell surfaces for critical life processes, such as cell communication, cell adhesion, and immunological response. These proteins are excellent targets for drug design and the recent success in developing the COVID-19 vaccine is an example. In industries, protein stability upon interactions with surfaces can greatly impact product quality, such as food packaging and drug delivery systems. Also, proteins are incorporated on surfaces for making biosensors and molecular devices. Therefore, being able to predict protein behaviors on various surfaces can help advance fundamental knowledge and develope new drugs and materials. Nonetheless, proteins on surfaces cannot function by themselves. Not only do they interact with the surface materials (e.g., cell membrane and plastic packages), they are also integrated with surrounding water molecules. These water molecules determine protein structures and functions, and thus must be considered to fully understand and predict protein behaviors. Professor Yan will develop a new optical technique with unprecedented selectivity for detecting water molecules and their interactions with proteins on surfaces. Combining experimental and computational methods, Professor Yan will develop approaches to generate detailed descriptions of these water molecules interacting with various types of proteins on surfaces. Professor Yan will provide training opportunities to students at various levels in conducting scientific research and organize students to reach out to a neighborhood high school to support their STEM education program and hold panel discussions on STEM career opportunities. The project will develop external heterodyne chiral vibrational sum frequency (SFG) generation spectroscopy to probe protein hydration at interfaces. This method is expected to have the advantages of being in situ, real-time, and label-free. More importantly, it will provide unique selectivity to water molecules surrounding proteins that are in folded chiral structures without interference of background signals from interfacial and bulk water. The project will construct an external heterodyne SFG spectrometer to acquire water O-H stretching spectra at the air/water interface in the presence of proteins that with attention to their secondary, tertiary, and quaternary structures. Molecular dynamics (MD) models being constructed at the interface will be used to simulate the phase-resolved chiral SFG spectra. The comparison of the experimental and computational spectra in conjunction with analyses of the MD trajectories will allow for extraction of information about topology and local interactions of water molecules around the proteins. Finally, the combined experimental and computational approaches will be used to investigate changes in water structures during protein denaturation on surfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.