LIPID CONTROL OF MEMBRANE PROTEIN ORGANIZATION

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The long term objective of this work is to determine the conformational changes that occur in proteins and phospholipids upon their mutual interaction. The principles involved will provide a basis for understanding the molecular organization of biological membranes and how the organization may be altered during pathological conditions. Three specific aims will be addressed to achieve this objective: (1) To determine whether integral membrane proteins preferentially partition into regions of specific chemical structure or physical order in complex phospholipid environments, and to determine the relationship of any observed partitioning to the function of membrane-bound enzymes. (2) To determine the site and magnitude of the interactions produced by membrane proteins and membrane-active peptides on phospholipid molecules. (3) To determine changes in conformation and orientational order that occur in both the phospholipid and protein components upon their mutual interaction in model vesicle and planar bilayer systems, and in a reasonably simple native preparation (lung surfactant) to be studied in vitro. The main physical method to be employed to study in non- perturbative fashion both lipid configuration and protein secondary structure is Fourier Transform Infrared (FT-IR) spectroscopy. The thermodynamics of lipid-protein interactions is evaluated with high sensitivity Differential Scanning Calorimetry (DSC). To achieve Aim 1, CaATPase from rabbit sarcoplasmic reticulum is isolated, purified, and reconstituted into phospholipid environments selected to mimic those in vivo. The miscibility and partitioning characteristics of the system are determined with FT-IR and DSC. Aim 2 is achieved by reconstitution of the desired membrane protein or peptide with phospholipids deuterated at specific positions in the acyl chains. Perturbations at the specific site in the latter will be monitored with attenuated total reflectance spectroscopy. Aim 3 is addressed by determination of the type and geometric orientation of protein or peptide secondary structure via the conformation-sensitive Amide I or II spectral regions. The organizational principles deduced through the above experiments will be extended to a simple native tissue, lung surfactant, to be studied in vitro. The molecular basis of the stability and spreading of surfactant at the air-water interface will be probed.