Enhanced membrane-perturbing activities of bundled amphiphilic α-helix polypeptides on interaction with phospholipid bilayer

The 24-peptide 4₆, designed to take an amphiphilic α-helix structure, had strong activity toward phospholipid membranes and could form ion-channels selective for cations on a planar membrane [J. Biol. Chem., 266, 20218 (1991)]. Four, six, and eight segments of the peptide 4₆ were bundled (4α-4₆, 6α-4₆, and 8α-4₆) on dendrimers consisting of Lys residues. These bundled peptides had highly α-helical structures with an enhanced α-helicity compared with the original 4₆ peptide. These peptides had hydrophobic pockets inside the bundle structures in aqueous solution in which the fluorescent hydrophobic probe, 1-anilino-8-naphthalenesulfonate (ANS), bound strongly. The peptides caused much leakage of carboxyfluorescein from small unilamellar vesicles of phospholipids at much lower concentrations of peptides than 4₆ did. Furthermore, the peptides induced the vesicle fusion at lower concentrations than those of the leakage. Four segments of the analogous 24-peptide 4₆S, in which six Ser residues were introduced instead of Ala and Leu residues in 4₆, were bundled by the same method (4α-4₆S). The fluorescent properties of the Trp residues incorporated at the 1 and 12 positions in 4α-4₆S, respectively, indicated that the centers of the helices were in more hydrophobic conditions than the N-terminal was. These facts caused us to conclude that the bundled conformation increased the perturbation of the phospholipid membrane, and as a result, the peptides were embedded in the membrane.