Studies on Conformation Analysis of Functional Peptides in Lipid Double Layr by UV Resonance Raman Spetrometry

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UV resonance Raman spectrometry using 193nm for excitation is useful for the elucidation of the structures of peptides and proteins in various enviroments, since that enables to observe the amide bands of these compounds selectively. The purpose of this work is the analysis of the conformation of functional peptides, Boc- (Ala-Aib) _n-OMe (n=2,4,8), and their aggregation in bimolecular lipid membrane. Raman spectrometric measurement was carried out by using an Ar/F excimer laser as a light source and a multiple wave detection method. Raman signals to be ascribed to amide I,II,III and 2V were observed from the peptide which existed in liposome made from dimyristoyl phosphatidylcholine. The wavenumbers of the amide bands oberved from Boc- (Ala-Aib) _8-OMe exising in the lipid membrane were in fair accord with those from poly (L-lysine) , whose structure was ascribed to alpha-helix based on its CD spectrum. Thus, it suggests the hexadecamer of that peptide in lipid membrane has the alpha-helix structure. In addition, the structures of the tetramer and the octamer were confirmed : an irregular structure for the tetramer and the 3_<10> structure for the octamer. An explicit correlation was confirmed between the observed wavenumbers of the amide bands and the secondary structure of peptides. A shift of the amide V band to higher wavenumber for a peptide aggregate was expected from the calculation of normal vibration mode based on molecular dynamics and that agreed with the results observed with higher concentration of Boc- (Ala-Aib) _8-OMe. It suggests the number of intramolecular hydrogen bond or the stbility of the conformation is decreased because of the distorted structure of the associated peptide.