Structural plasticity of the feline leukaemia virus fusion peptide: a circular dichroism study.

The secondary structure of the feline leukaemia virus (FeLV) fusion peptide was investigated using circular dichroism (CD). Our results show that this peptide can readily flip between random, alpha-helical and beta-sheet conformations, depending upon its environment. The CD spectrum changes from one characteristic of random coil to predominantly beta-sheet type, and finally to that showing the characteristics of alpha-helical structure on moving from an aqueous solvent, through several increasingly hydrophobic systems, to a highly hydrophobic solvent. Electron microscopy confirmed the presence of beta structure. We propose that the structural plasticity demonstrated here is crucial to the ability of the fusion peptide to perturb lipid bilayers, and thus promote membrane fusion.