Probing structures and hydration of biopolymers at aqueous interfaces using chiral-selective vibrational sum frequency generation spectroscopy - Project Summary/Abstract Biopolymers (proteins, DNA, and RNA) that are stable in solution often change conformations at the aqueous interfaces. Understanding this phenomenon will help elucidate many fundamental biological functions (e.g., membrane protein folding) and help design biomaterials (e.g., drug delivery systems). Aqueous interfaces are the boundaries between water and another medium—such as a cell membrane, biomolecular condensate, or mineral—where the water hydrogen-bonding network is terminated, resulting in asymmetric chemical environments. The key unanswered question is how the asymmetric chemical environments of interfaces modulate hydration and thus structures of the biopolymers. Addressing this question requires a physical method with surface selectivity to suppress signals from the bulk solution, as well as selectivity to distinguish biopolymer folding and isolate water signals from the hydration shells. Current methods are limited in providing such selectivity, hindering the fundamental understanding of biological functions at aqueous interfaces. Our recent progress showed that chiral-selective vibrational sum frequency generation spectroscopy (chiral SFG) can provide the necessary selectivity. It can detect protein and DNA secondary structures and probe their first hydration shell at aqueous interfaces. In this MIRA project, we will first investigate three fundamental questions about protein stability at interfaces: (1) Does the first hydration shell of proteins at interfaces undergo a phase transition melting process during protein melting? (2) How does molecular crowding impact water structures in the first hydration shell of proteins at interfaces? (3) How do denaturants and stabilizers perturb the first hydration shell of proteins at interfaces? Also, we will develop chiral SFG for probing higher- order structures of biopolymers. We will obtain homogeneous isoforms of the amyloid fibrils from Dr. Robert Tycko (NIH) and correlate their distinct molecular symmetry with chiral SFG responses of various vibrational modes. Finally, we will develop chiral SFG for characterizing small-molecule drug binding to DNA. We will detect displacement of water from the first hydration shell using minor groove binders, major groove binders, and intercalators, thus establishing chiral SFG signals of water as reporters for site-specific binding to DNA. In carrying out this MIRA project, we will collaborate with theorists, Profs. Sharon Hammes-Schiffer (Princeton) and Victor Batista (Yale), to simulate the chiral SFG spectra of molecular systems that mimic our experiments in order to build a theoretical basis for interpreting experimental data and advancing chiral SFG as a quantitative approach for elucidating biological function at interfaces at the fundamental level. Hence, this MIRA project will develop and apply chiral SFG for detecting the interplay of interfaces, chirality, and water in modulating structures of biopolymers to understand the principles, mechanisms, and processes taking place at aqueous interfaces in living organisms. Our findings will lay the foundation to develop new technologies and advance fundamental knowledge for solving problems in biomedical sciences.
