In broad terms, the goal of this research is to obtain a better understanding of membrane structural properties and their relationship to biological function. These basic studies will contribute significantly to general medical research as well as to research in heart and muscle diseases. New experimental and theoretical methods will be developed for the study of the structural and dynamic properties of lipid bilayers and their interactions with cholesterol and integral membrane proteins. A series of different lipid bilayers and membranes containing the Ca2+-ATPase from sarcoplasmic reticulum will be investigated using nuclear magnetic resonance (NMR) techniques. Deuterium NMR will be used to derive order parameters for the individual bond segments of the lipid and protein molecules in the liquid-crystalline state to yield new structural information. The dependence of the spin- lattice relaxation rates on the segmental ordering, resonance frequency, and bilayer orientation will be studied using one- and two-dimensional (2-D) NMR methods. The results will then be used to critically evaluate different theoretical models for the molecular dynamics of lipid bilayers. The experimental studies will include detailed investigations of the influences of acyl chain length, polar head group, and degree of hydration on bilayer physical properties. Similar studies of phospholipid membranes containing cholesterol or the Ca2+-ATPase will be performed. Carbon-13 NMR studies of phospholipid bilayers and biomembranes will be conducted at natural abundance or with isotopically enriched samples using novel solid-state techniques. Dipolar tensors will be determined from 2-D NMR experiments to derive order parameters for the individual bond segments of the lipid and protein moieties. The carbon-13 NMR studies will also involve spin-lattice relaxation rate measurements in the laboratory- and rotating-coordinate frames. In addition, high-resolution proton and carbon-13 NMR studies of the Ca2+-ATPase and its 20 kD tryptic fragment in detergent micelles and membranes will be carried out. From these results, a unified picture for the structural dynamics of membranes will be developed. Finally, NMR studies of membranes containing the Ca2+-ATPase will be correlated with studies of their ATP-hydrolyzing and calcium translocating activities to relate their structural and dynamic properties to function.
