SECONDARY STRUCTURE OF THE MEMBRANE-BOUND FORM OF THE PORE-FORMING DOMAIN OF COLICIN-A - AN ATTENUATED TOTAL-REFLECTION POLARIZED FOURIER-TRANSFORM INFRARED-SPECTROSCOPY STUDY

The structure of the pore-forming domain of the bacterial toxin colicin A was studied by attenuated total-reflection polarized Fourier-transform infrared spectroscopy. This channel-forming fragment interacts with dimyristoylglycerophosphoglycerol (Myr2GroPGro) vesicles and forms disk-like complexes. Analysis of the shape of the amide I' band indicates that its secondary structure is not affected by the pH 5.0-7.2. However, 5-10% of the peptide amino acids adopt an alpha-helical structure upon complex formation with Myr2GroPGro, while the random-coil and beta-sheet structure contents decrease. Interestingly, the increase in alpha-helical content is essentially due to an increase in the high-frequency component of the alpha-helical domain of amide I'. The fact that only this component was 90-degrees polarized (i.e. the helix is parallel to the acyl chain) suggests that only this particular type of helix is associated with the Myr2GroPGro bilayer.