Elucidation of protein-lipid interactions in a lysozyme-corn oil system byFourier transform Raman spectroscopy

Lysozyme (25% in D2O), corn oil, and their emulsions (10% w/w oil/D2O solut ion) were examined by Fourier transform Raman spectroscopy. Emulsions showe d three layers, namely, top oil, middle cream, and bottom aqueous layers. R aman spectral analysis revealed hydrophobic interactions involving both pro tein and lipid components. Compared to lysozyme in D2O, the difference spec trum obtained after subtraction of oil from the cream layer spectrum showed reduced intensity of tryptophan bands at 760, 1013, 1340, and 1360 cm(-1), reduced intensity ratio of the tyrosine doublet at 850 and 830 cm(-1), and increased intensity of the C-H bending band at 1455 cm(-1). Compared to co rn oil, the difference spectrum after subtraction of lysozyme from the crea m layer spectrum indicated decreased intensity at 2855 cm(-1) (lipid CH2 sy mmetric stretch) and 3011 cm(-1) (unsaturated fatty acid hydrocarbon chain =C-H stretch) and a higher intensity ratio of the C-H stretching band at 29 00 cm-(1) to bands at 2885 and 2933 cm(-1). Spectra of the top and bottom l ayers resembled corn oil and lysozyme, respectively, except for changes in the D2O band. Raman spectroscopy can be used to detect structural changes i n proteins, lipids, and D2O due to;protein-lipid interactions.