(683a) Determination of Orientation and Conformation of Lysozyme at the Air-Water Interface Using an Integrated MD/SFG Approach

Proteins have markedly complex and diverse structures due to a high variability in size, shape, amphiphilicity, and charge needed to carry out their biological function. The interfacial behavior of adsorbed proteins govern properties such as foaming and stabilization, relevant to applications in pharmacy, biotechnology, and the food industry.^1-2 By studying proteins at the air water interface (AWI), which occurs naturally in many biological processes, we can explore how conformation and orientation of these complex biomolecules lead to self-assembly at these interfaces. To date, the interfacial structure of even one of the most widely studied proteins, lysozyme, remains unresolved.

In this talk we describe our approach to uncovering this interfacial structure by combining molecular dynamics simulation, vibrational sum frequency generation (SFG) spectroscopy, and spectral calculations to determine the conformation and orientation of lysozyme at the AWI. Computationally, two force fields are used to simulate lysozyme. With this approach we determine agreement in a single interfacial pose at high atomistic resolution. We validate the proposed structure of lysozyme by comparing signals of experimentally derived structures, to the spectra calculated from simulation, showing strong agreement by the pose predicted by MD. Lastly, we provide additional atomistic insight, discussing how pH may lead to an orientation change from head on to side-on at the interface, explaining previous discrepancies in the literature with regards to the thickness of the experimentally derived monolayers. This work provides a template for future studies of proteins at interfaces to make maximum use of integrated computational and experimental approaches.

[1] Dickinson, E. Proteins at Interfaces and in Emulsions Stability, Rheology and Interactions. J. Chem. Soc. Faraday Trans. 1998, 94 (12), 1657–1669.

[2] McClements, D. J. Protein-Stabilized Emulsions. Curr. Opin. Colloid Interface Sci. 2004, 9 (5), 305–313.