Molecular Design and Structure-Function of Ion Transfer Peptides : Investigation of structural stabilizing factor, Trp and Functional Factor, Glu

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Peptaibols form alpha-helical structures leading to voltage-dependent ion channels in lipid membranes. It has been confirmed that 2-aminoisobutyric acid (Aib)-containing peptides tend to take alpha-helix conformations and form voltage-dependent channels in lipid bilayrs. In the present study, amphiphilic helical Aib-containing peptides with various chain lengths, Ac- (Aib-Lys-Aib-Ala) n-NH2 (n=1-5 ; named as BKBA-4,8,12,16 and 20, respectively) have been designed to investigate the aggregation and transmembrane orientation of Aib-containing helical motifs in lipid bilayrs.Peptide synthesis was carried out by a solid-phase method. CD spectra of BKBA-4 and BKBA-8 in the buffer exhibited a weak band at 200 nm, representative of non-ordered structure. CD spectra of peptides having longer peptide chains, BKBA-12,16 and 20, exhibit the typical double minimum bands, characteristic of alpha-helix. The helicities of the peptides increased with increasing of chain length. In particular, BKBA-16 and 20 took almost complete a-helical structures (77 and 85%, respectively). In TFE,BKBA-12,16 and 20 also displayd significant a-helical contents. From comparing the CD spectra of the peptides in the buffer and TFE,the band at 208 nm increases dramatically in TFE.The reversal of the ellipticity ratio of 208 to 225 nm in TFE may reflect the transition from an aggregated state in buffer to single stranded helices in TFE.Moreover, the alpha-helical structures were intensified in phospholipid liposomes. Especially, CD characteristics of BKBA-16 and 20 were very close to those of alamethicin. These results suggest that BKBA-16 and 20 may aggregate and form alamethicin-like barrel-stave conformations in phospholipid bilayrs. This structure can be also confirmed by the formation of stable conducting pores in bilays, using patch-clamp methodology.