Probing Residue-Specific Water-Protein Interactions in Oriented Lipid Membranes via Solid-State NMR Spectroscopy.

Water plays a central role in membrane protein folding and function. It not only catalyzes lipid membrane self-assembly but also affects the structural integrity and conformational dynamics of membrane proteins. Magic angle spinning (MAS) solid-state NMR (ssNMR) is the technique of choice for measuring water accessibility of membrane proteins, providing a measure for membrane protein topology and insertion within lipid bilayers. However, the sensitivity and resolution of membrane protein samples for MAS experiments are often dictated by hydration levels, which affect the structural dynamics of membrane proteins. Oriented-sample ssNMR (OS-ssNMR) is a complementary technique to determine both structure and topology of membrane proteins in liquid crystalline bilayers. Recent advancements in OS-ssNMR involve the use of oriented bicellar phases that have improved both sensitivity and resolution. Importantly, for bicelle formation and orientation, lipid bilayers must be well organized and hydrated, resulting in the protein's topology being similar to that found in native membranes. Under these conditions, the NMR resonances become relatively narrow, enabling a better separation of