Abstract

We investigated the modes interaction of mastoparan B, model peptide Ac-(Leu-Ala-Arg-Leu)_3-NHCH_3 (4_3) and gramicidin S, amphiphilic peptides with biomembranes. As a result, we observed morphological changes in erythrocytes and bacterial membranes. Mastoparan B caused a change in the shape of erythrocytes from normal discoid to a crenated form (named echinocytes). The major morphological changes of Staphylococcus aureus 209P induced by 4_3 and gramicidin S were the destruction of the cell wall and the accumulation of large enectron-opaque structures in the ccytoplasm. The damage was initiated by gap formation in the cell wall. In the freeze-fracture method, heavy damages occurred in the cell membrane. The cell wall became thin and finally ruptured. The protoplasts prepared from the 4_3-treated bacteria were unstable in an osmotically controlled vuffer and lysed within 2 hr, whereas those prepared from control cell and 4_3treated protoplasts were stable for more than 3 hr. These structural changes were not specific for 4_3 but were also found in gramicidin S-treated cells. Therefore, we expect that the bactericidal mechanism of 4_3, an amphiphilic linear peptide, and gramicidin S, an amphiphilic cyclic peptide, on Staphylococcus aureus 209P will by basically the same. In the case of erythrocytes, their transformation to echinocytes by mastoparan B should be similar to the way in which the transformation is caused by amphiphilic basic peptides such 4_3 and gramicidin S.

• Keywords: Gramicidin S; mastoparan B; model peptide; Ac-(Leu-Ala-Arg-Leu)_3-NJCH_3 (4_3); morphological change