The structure and dynamics of water has captivated the interest of researchers for decades, motivated in large measure by the importance of these properties in biological systems at interfaces. However, techniques that can routinely deal with delicate, dynamic, and heterogenous natural systems, such as proteins embedded near or in lipid membranes, remains an area of active development. Magnetic Resonance (MR) experiments rely on resonance frequencies many orders of magnitude slower than those of, e.g., ultrafast laser experiments that have shown earlier promise for interrogating interfacial systems. Nonetheless, MR relaxometry techniques can still probe fast molecular dynamics in the frequency domain through a set of techniques known as relaxometry. These techniques prove capable of dealing with very heterogeneous systems.<br/><br/>The NMR-ESR dual-resonance technique known as ODNP (Overhauser Dynamic Nuclear Polarization) can amplify signal from the surface layer against a bulk background, and also move to much faster timescales, thus unlocking a capability to interrogate the dynamics of water molecules in the hydration layer. This technique comes with many of the advantages inherent in traditional NMR, such as directly measuring – rather than inferring – nuclear motion. Furthermore, ODNP does not rely on higher-order spectroscopic effects, requires only a simple, versatile, and non-perturbative labeling strategy, and functions seamlessly in opaque, viscous, and other experimentally difficult systems. Notably, ODNP can interrogate differences in hydration water residing in different patches on the surface of the same macromolecule.<br/><br/>In this talk, I focus on two key ongoing investigations in our group. First, we look at the surface interface of a transmembrane helix of the light-activated proton pump proteorhodopsin. Understanding interactions between this protein and the surrounding lipid environment are key to ongoing efforts to engineer this protein and integrate it into synthetic membranes, and yet even more native-like surfactant environments remain sparsely explored. We perform measurements of water permeating into the lipid layer and then manipulate this behavior through specific ion effects. Next, we look at a globular signaling protein (K-Ras) and begin to directly explore the energy required to displace water molecules in the hydration layer by way of a practicable temperature-controlled ODNP measurement.

Heterogeneous hydration layer encasing proteins and its interaction with lipid molecules

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.