Oriented circular dichroism of a class A amphipathic helix in aligned phospholipid multilayers.

The effect of lipid phase state on the orientation and conformation of a class A alpha-helical peptide on aligned lipid multilayers was examined using oriented circular dichroism spectroscopy. A comparison of oriented spectra in aligned peptide-lipid multilayers with CD spectra of unaligned peptide lipid vesicle complexes is consistent with a preferential alignment of helices parallel to the membrane surface at temperatures above and below the main acyl-chain melting transition temperature of the phospholipid. Changes are observed in the oriented CD spectra with lipid phase state which are attributed to a subtle conformational change of the peptide on the lipid surface. The results are compared with available experimental data on membrane-active lytic and antimicrobial helical peptides.