Secondary structure of sea anemone cytolysins in soluble and membrane bound form by infrared spectroscopy

Attenuated total reflection (ATR) Fourier transform infrared spectroscopy ( FTIR) was used to investigate the secondary structure of two pore-forming c ytolysins from the sea anemone Stichodactyla helianthus and their interacti on with lipid membranes. Frequency component analysis of the amide I' band indicated that these peptides are composed predominantly of beta structure, comprising 44-50% beta-sheet, 18-20% beta-turn, 12-15% alpha-helix, and 19 -22% random coil. Upon interaction with lipid membranes a slight increase i n the alpha-helical and beta-sheet structures was observed with a concomita nt decrease of the unordered structure. Polarisation experiments indicated that both toxins had some disordering effect on the lipid layers. The dichr oic ratio of the cu-helical component of the membrane-bound toxin was 3.0-3 .3, indicating that this element was oriented with an angle of 38 degrees-4 2 degrees with respect to the normal to the plane of the crystal surface, t hus resulting almost parallel to the mean direction of the lipid chains, (C ) 1999 Academic Press.