Design and conformation of non-Aib synthetic peptides enjoying alamethicin-like ionophore activity

Analogues of alamethicin, a 20-mer amphipathic helical peptide with ionophore activity, in the sequence of which all Aib residues were substituted by Ala (A1) or Leu (L1), were synthesized by the solid phase method, purified by high performance liquid chromatography and characterized by fast atomic bombardment mass spectrometry. Infrared and CD studies showed that A1 easily underwent a transconformation to beta-structure whereas L1 displayed a predominant alpha-helical character, thus being a potential ionophore model. Its voltage-dependent multistate activity in model membranes showed that Aib is not a requisite residue to observe an alamethicin-like behavior. However, as the lifetime of the single channels was much shorter than for alamethicin, the peptide chain was lengthened by a Leu (LL1) or a Ser (SL1) residue. The last peptide gave an increased channel lifetime, but the design of other non-Aib peptides, taking into account the hydroxyl C-terminus and side-chain interactions between helices in a barrel-stave bundle, is desirable to approach more closely the alamethicin activity.