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

在耶鲁大学化学系生命过程化学（CLP）项目的支持下，耶鲁大学严翠英教授正在开发一种新的光学方法，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。它们中的许多位于细胞表面，参与细胞通讯、细胞粘附和免疫反应等关键生命过程。这些蛋白质是药物设计的极好靶点，最近成功开发的COVID-19疫苗就是一个例子。在工业中，蛋白质与表面相互作用的稳定性可以极大地影响产品质量，例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装置。因此，能够预测蛋白质在各种表面上的行为可以帮助推进基础知识和开发新的药物和材料。然而，表面上的蛋白质不能单独发挥作用。它们不仅与表面材料（如细胞膜和塑料包装）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，因此必须考虑到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，该技术具有前所未有的选择性，可以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上各种蛋白质相互作用的详细描述。严教授将为不同层次的学生提供进行科学研究的培训机会，并组织学生到社区高中支持他们的STEM教育计划，并就STEM职业机会举行小组讨论。该项目将开发外外差手性振动和频率（SFG）产生光谱来探测界面处的蛋白质水合作用。该方法有望具有原位、实时和无标签的优点。更重要的是，它将对处于折叠手性结构的蛋白质周围的水分子提供独特的选择性，而不会干扰界面水和大量水的背景信号。本项目将构建外差SFG光谱仪，在蛋白质存在的情况下获取空气/水界面的水O-H拉伸光谱，并关注其二级、三级和四级结构。在界面处建立的分子动力学（MD）模型将用于模拟相分辨手性SFG光谱。将实验光谱和计算光谱的比较与MD轨迹的分析结合起来，可以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用于研究蛋白质变性过程中表面水结构的变化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.