NMR Lateral Diffusion Measurements in Biomembranes

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Nuclear magnetic resonance (NMR) spectroscopy has revolutionized the measurement of diffusion, since the introduction of the pulsed field gradient (PFG) NMR diffusion technique, which is now routinely applied in a multitude of chemical and biological systems and situations with enormous success. However, in biological membranes, whether model or real, the PFG NMR diffusion method has contributed considerably less, due to the inherent challenges of the membrane environment. These include broad NMR resonance lines, poor resolution, and the large range of diffusion rates which can vary by orders of magnitude from "fast" diffusing small drug molecules, to "slow" diffusing large anchored membrane proteins. Such "lateral" diffusion within membranes is a fundamental property of the proteins, lipids and other biomolecules of which membranes are constituted, is critical for proper membrane functioning, and can reveal key aspects of structure-function relations hitherto unrecognized. We have introduced several new approaches to NMR diffusion measurements in membranes that overcome many of the inherent barriers. The primary objectives of the research program proposed here are to exploit these approaches in the investigation of several important biomembrane phenomena. In particular, we will investigate the energy of the associations between transmembrane alpha-helical peptides with the goal of understanding the energy hierarchy of the different means by which such associations occur. Also, we will examine domains in membranes, which are long-lived regions of distinct composition and function, but which remain poorly characterized, much less understood. Finally, we will continue to refine our new model membrane system, which is a hybrid of a lipid bilayer supported on a "smart" polymer hydrogel sphere, and which exhibits particular advantages as a model system for diffusion and other fundamental and applied studies.