ENHANCED MEMBRANE-PERTURBING ACTIVITIES OF BUNDLED AMPHIPHILIC ALPHA-HELIX POLYPEPTIDES ON INTERACTION WITH PHOSPHOLIPID-BILAYER

The 24-peptide 4(6), designed to take an amphiphilic alpha-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 4(6) were bundled (4 alpha-4(6), 6 alpha-4(6), and 8 alpha-4(6)) on dendrimers consisting of Lys residues. These bundled peptides had highly alpha-helical structures with an enhanced alpha-helicity compared with the original 4(6) peptide. These peptides had hydrophobic pockets inside the bundle structures in aqueous solution in which the fluorecent 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 4(6) did. Furthermore, the peptides induced the vesicle fusion at lower concentrations than those of the leakage. Four segments of the analogous 24-peptide 4(6)S, in which six Ser residues were introduced instead of Ala and Leu residues in 4(6), were bundled by the same method (4 alpha-4(6)S). The fluorescent properties of the Trp residues incorporated at the 1 and 12 positions in 4 alpha-4(6)S, 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.