Circular dichroism studies on lipid-protein complexes of a hydrophobic myelin protein

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Abstract
Circular dichroism spectra of lipophilin (a hydrophobic protein purified from human CNS myelin) were analyzed by the method of Chen et al. to obtain information on its secondary structure in aqueous and lipid environments. When introduced into phosphatidylcholine vesicles by dialysis from 2-chloroethanol, the protein possessed about 75% .alpha. helix. A new water-soluble form of lipophilin also containing over 70% .alpha. helix was obtained by a similar dialysis in the absence of lipid. This product had a higher helical content than 2 other water-soluble preparations derived by dialysis from phenol-acetic acid-urea. Interaction of all 3 aqueous forms of the protein with lysolecithin micelles resulted in increases in total helical content or in the average length of helical segments. The amount of .beta. sheet was at a minimum for lipophilin incorporated into vesicles, where the presence of lipid also provided some protection against thermal denaturation.