The long-term objective of this project is to determine how proteins associate with phospholipids. These proteins have, for the purposes of this proposal, been restricted to two types of helical proteins; these are surface associating peptides (SAPs) and membrane spanning peptides (MSPs). The former include many of the plasma apolipoproteins as well as certain polypeptide hormones. The latter includes many integral membrane proteins, although the difficulty in purifying some of this group has kept the number of known examples small. Using synthetic peptide analogs of the SAPs and MSPs in model lipid membranes, we will identify a number of correlations between their primary structure and their behavior that will be useful for predictive purposes. Using equilibrium techniques we will identify specific sequence patterns in the SAPs that affect their affinity (lipophilicity) for phospholipid surfaces; these include the effects of helix breakers, the depth of penetration of hydrophobic residues into the lipid surface, and the arrangement of polar and non-polar amino acid residues in the helical peptide. We will identify the amino acid residues in model MSPs that give them """"""""globular"""""""" character in a lipid bilayer, and demonstrate that MSPs and SAPs may be distinguished by the relatively larger number of lipid molecules that are perturbed in the latter instance. High sensitivity differential scanning calorimetry forms the cornerstone of this part of the project. Other major techniques include equilibrium dialysis, fluorescence, circular dichroism, and peptide synthesis. The results of this investigation will be useful in the validation and refinement of models for lipid-protein interaction that can be used to design and synthesize analogs of natural lipid associating peptides.
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