Secondary structure and association of melittin during and after solid‐phase synthesis: a Raman and static light scattering study

The solid-phase synthesis of melittin, a haemolytic peptide containing 26 amino acid residues, was monitored by near-infrared Fourier transform Raman spectroscopy. The resin used was Tenta Gel S RAM. The secondary peptide structure was investigated for each step in the synthesis. A random coil secondary structure was the most probable in all cases, and accordingly all steps in the synthesis gave good yields. Melittin cleaved from the resin showed an α-helix secondary structure in the solid state. Raman spectra were obtained for 10, 5, 4, 2 and 1% (w/w) aqueous solutions. The 1 and 2% solutions showed too weak melittin bands to be able to draw conclusions about the secondary structure. However, the more concentrated solutions evidently showed an α-helical structure. Simultaneous static light scattering, refractive index measurements and exclusion chromatography on synthetic melittin in 50 mM phosphate (pH 7) and 150 mM NaCl showed the presence of dimers and tetramers in the eluted liquid. No evidence of monomers or trimers was found. Copyright © 2002 John Wiley & Sons, Ltd.