**1.5.5 Insect defensins**

The insect defensin class have an alpha-helix secondary structure bound to the beta sheet. Their structures are similar to another arthropod peptide class: the scorpion potassium channel blocker toxins (Bontems et al., 1991). Study of the structural features involved in the antimicrobial activity of longicin, a defensin from the hard tick *Haemaphysalis longicornis*, showed that the beta sheet alone was sufficient for antimicrobial activity. This part of the insect peptide is positively charged at neutral pH, as does the alpha helix of the same, nevertheless the role of the alpha-helix, at the antimicrobial level, seems to be restricted to maintain the globular shape of the peptide (Rahman et al., 2009).

*R. prolixus* insect defensin B ATCDLLSFRSKWVTPNHAGCAAHCLLRGNRGGHCKGTICHCRK
