Carbonyl vibrations have become useful probes of structure and dynamics in biological systems. Increasingly accurate models coupled with state-of-the-art MD simulations have helped extract a molecular view of protein structure and dynamics from experimental amide I spectra. Despite the large diversity of C=O groups in biological molecules, other probes such as ester carbonyls have, thus far, received little attention. Our research focuses on using ester C=O vibrations of lipids as local probes of the interface in lipid membranes. Carbonyls are located precisely at the 1-nm-thick interface between bulk water and the hydrophobic membrane core where important biological processes take place. IR spectroscopy provides a detailed view of the interface. For example, the number and lifetime of water-C=O hydrogen bonds can be directly extracted from IR and 2D IR spectra. In this talk I will discuss the development of spectroscopic models to extract structural information, such as lipid phase, and lipid-lipid interactions at the lipid-water interface from 2D IR spectra. The models are designed to accurately reproduce the IR absorption lineshapes of ester carbonyls in a broad range of environments. I show how IR lineshapes are sensitive to the lipid phase (gel, liquid ordered, liquid disordered) in model membranes, and how the number of lipid-water hydrogen increases upon transitioning from the gel to the liquid phase. I will also discuss the effects of membrane heterogeneity and how different lipid species induce local disorder. Finally, I will show how amide I to ester C=O coupling depends on protein orientation and protein-lipid interactions. Our group currently measuring protein-lipid interactions in small membrane-bound peptides in order to understand the role of the membrane in the folding mechanism of these peptides.

Investigating lipid membrane interfaces with 2D IR spectroscopy

253rd National Meeting (2017)

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