INFLUENCE OF PROLINE POSITION UPON THE ION-CHANNEL ACTIVITY OF ALAMETHICIN

Alamethicin, a 20-residue peptaibol, induces voltage-dependent ion cha nnels in lipid bilayers according to the barrel-stave model. To study relationships between the proline-14-induced kink region and the chann el-forming behavior of the peptide, a set of alamethicin analogs with proline incorporated at positions 11, 12, 13, 14, 15, 16, and 17, resp ectively, as well as an analog with alanine instead of proline at posi tion 14 were synthesized. Macroscopic conductance experiments show tha t the voltage dependence of the peptides is conserved although slightl y influenced, but the apparent mean number of monomers forming the cha nnels is significantly reduced when proline is not located at position 14. This is confirmed in single-channel experiments. The analogs with proline next to position 14 (i.e., 13, 15, 16) show stable conductanc e levels, but of reduced number, which follows the order Alam-P14 > Al am-P15 > Alam-P16 > Alam-P13. This reduction in the number of levels i s connected with changes in the lifetime of the channels. Analogs with proline at position 11, 12, or 17 produce erratic, extremely short-li ved current events that could not be resolved. The changes in function al properties are related to structural properties as probed by circul ar dichroism. The results indicate that proline at position 14 results in optimal channel activity, whereas channels formed by the analogs b earing proline at different positions are considerably less stable.