Secondary structure of the hydrophobic myelin protein in a lipid environment as determined by Fourier-transform infrared spectrometry.

The secondary structure of a hydrophobic myelin protein (lipophilin), reconstituted with dimyristoylphosphatidylcholine or dimyristoylphosphatidylglycerol, was investigated by Fourier-transform infrared spectroscopy. Protein infrared spectra in the amide I region were analyzed quantitatively using resolution enhancement and band fitting procedures. Lipophilin in a phospholipid environment adopts a highly ordered secondary structure which at room temperature consists predominantly of alpha-helix (approximately 55%) and beta-type conformations (36%). The secondary structure of the protein is not affected by the lipid gel to liquid crystalline phase transition. Heating of the lipid-protein complex above approximately 35 degrees C results in a gradual decrease in alpha-helical content, accompanied by an increase in the amount of beta-structures. Lipophilin dissolved in 2-chloroethanol is, compared to the protein in a lipid environment, richer in the alpha-helical conformation but still contains a sizable amount of beta-structure.