**1.1.3 Cecropin peptides**

Cecropin peptides were first purified from insect hemolymph, and their expression is usually inducible. Cecropins structural conformations were determined by NMR. Circular dichroism and NMR (Nuclear Magnetic Resonance) data have shown that in aqueous solvent the cecropin structure is largely disordered; but they adopt a stable alpha-helical secondary structure in more hydrophobic environment. This makes the insertion of these peptides in the lipidic membranes entropically favorable. Cecropin usually present a glycine in the middle of their amino acid sequence. This glycine has been proposed to induce a kink between the alpha helical structures that these peptides form in hydrophobic solvent. In turn the deletion of this glycine or its replacement by another amino acid do not eliminate the antimicrobial activity; instead it endows these mutant peptides with hemolytic and cytolytic activity (Moore et al., 1996). The cecropin usually present a tryptophan in one of the first two amino acid position as well as a glycine in the first position.

### **1.1.4 Magainin/scorpions AMP/cathelicidin peptides**

Magainin peptides come from the frog genus Xenopus (Duclohier et al., 1989). In this AMP class arthtropod AMP like Opistoporin-2 from Scorpion *Opistophthalmus carinatus* are also included (Moerman et al., 2002) as well as cathelicidin peptides (Travis et al., 2000) and the fly cecropin from *Stomoxys calcitrans* (Boulanger et al., 2002). This phylogenetically heterogeneous group present lysine/argine doublet repeats that could be considered as a structural signature. These peptides do not present the conserved glycine present in the other 2 lineal amphipatic AMP subclasses. Their positive general formal charge at neutral pH is higher than the one of the cecropin and dermaseptin AMP. They also present a conserved aspartic acid residue at the amino side of these peptides.
