Artificial ion channels formed by a synthetic cyclic peptide

A new cyclic peptide 1 having an (LLLD)(3) configuration pattern was design ed that is capable of forming artificial transmembrane ion channels by self -assembly of planar peptide rings, with hydrophilic groups arrayed in the i nterior of the channel. ion permeability in the presence of the synthetic p eptide 1, cyclo[-Trp-Dap-Leu-D-Ala-Trp-Ser-Val-D-Ala-Trp-Ser-Ile-Gly-] (Dap : L-diaminopropionic acid), was observed in lipid bilayer membranes. The pH dependence of ionic conductance showed that the beta -amino group of Dap m ay play a role in the conductance of the peptide channels. Fourier-transfor m infrared and circular dichroism data imply that, in a membrane, a stack o f cyclic peptides is formed in which the inter peptide H bonds form a kind of beta -structure analogous to that in the gramicidin A dimer and distinct from the H-bonding pattern of the beta -barrels.