Effect of the amino acid composition of cyclic peptides on their self-assembly in lipid bilayers.

Abstract

The effect of amino acid composition on the formation of transmembrane channels in lipid bilayers upon self-assembly of alt-(L,D)-α-cyclic octapeptides has been investigated. Cyclic peptides comprising D-leucine, alternating with different combinations of L-azidolysine, L-lysine(Alloc), L-lysine and L-tryptophan were synthesized and the size of pores formed via self-assembly of these molecules in lipid bilayers was elucidated using large unilamellar vesicle fluorescence assays and dynamic light scattering. Pore formation was examined in large unilamellar vesicles made up of egg yolk phosphatidylcholine or Escherichia coli total lipid extract. From these analyses, we have established that cyclic peptides with charged side chains form large pores while those with neutral side chains form unimeric pores. Furthermore, the cyclic peptides that consist of non-symmetric amino acid configurations possess a higher membrane activity than the cyclic peptides with a symmetric amino acid configuration. In addition, we have found that peptide amphiphilicity plays a vital role in selective partitioning between bilayers that consist of egg yolk phosphatidylcholine and those comprised of E. coli total lipid extract. These results suggest that selective transbilayer channel formation via self-assembly may be a viable alternative for many applications that currently use more expensive, multistep synthesis methods.