Dimerization of truncated melittin analogues results in cytolytic peptides

A synthetic peptide with the sequence of the first 20 residues of melittin and terminating with an additional cysteine amide was found to have cytolytic activity similar to that of melittin. It was apparent from MS data that the cysteine-terminating peptides had formed disulphide dimers. A peptide in which the thiol was blocked by iodoacetate showed no activity, whereas the same peptide blocked by acetamidomethyl showed activity marginally less haemolytic than that of melittin. Cytolytic activity of melittin analogues comprising the full 26 residues could be obtained with wide sequence permutations providing that a general amphipathic helical structure was preserved. In contrast, the activity of the dimers was dependent not only on retention of an amphipathic helix but also on certain individual residues and a free positive charge. A free N-terminus was essential for haemolytic activity. In addition, a lysine or arginine residue at position 7 and a proline at position 14 were found to be necessary for activity, although it was apparent that additional residues are important for retention of the full lytic potential.