**1.1.1 General properties**

The first peptide of this family discovered is the cecropin A from the pupae of the moth *Hyalophora cecropiae* (Steiner et al., 1981; Hultmark et al., 1982). This structure of AMP has been encountered in virtually all the multi-cellular organisms. Even if their sequences show some similarity, they are not all evolutionary linked. As such, they cannot be aligned as a whole, and are commonly separated in structural subclasses: Cecropin, magainin and dermaseptin AMP. This AMP class do share general common features: the lack of cysteine bridges, the tendency to form alpha helical secondary structure in relatively hydrophobic solvent, the net positive charge at neutral pH and hydrophobic residues interspersed every 3 amino acid, giving them an amphipatic nature. Indeed, basic amino acid side chains face predominantly one side of the alpha helix and hydrophobic residues are generally on the other side of the molecule. A global alignment of the linear peptides separates three different classes that could be broadly characterised as Dermaseptin, magainin and cecropin class of lineal amphipathic AMP. Most of these peptides share the present a glycine near the middle of their peptidic sequence.
