**3. Applications of CS**αβ **motif peptides**

Human beings have been using natural products containing CSαβ motif peptides for several hundreds years. The most well known natural products are sweet peptides of plants and scorpion venom. For their anti-microbial and pesticide abilities, in many cases, peptides with CSαβ motif are transfected into industrial crops to protect these transgenic plant from pathogens. In recent years, some of plant defensins are also screened and selected as antibiotics for therapeutic utilities. In this section, some peptides with therapeutic potential are selected and discussed.

### **3.1 Sweet peptide: Brazzein**

Brazzein is isolated from *Pentadiplandra brazzeana*, a climbing plant plant of the West Africa. Berry fruits of *Pentadiplandra brazzeana* have sweetness and are traditional foods of African natives (Assadi-Porter et al., 2008;Yang & Lyu, 2008). For a long time, the sweetness of the berry fruits is a secret. Ding and Hellekant at University Wisconsin Madison isolated a small peptide with sweetness from *Pentadiplandra brazzeana* and named it as brazzein 1994 (Ming & Hellekant, 1994). Peptide sequence analysis shows that brazzein contains a set of (*i, i+4*) and (*j, j+1*) cysteine pattern. Its NMR structure is solved and confirms it as a CSαβ motif peptide 1998 (Caldwell et al., 1998). Brazzein is the smallest, most heat-stable and pH-stable protein known to have an intrinsic sweetness (Jin et al., 2006). Brazzein is 200 times sweeter than sugar and it can be used both in cold and hot drinks/foods without change its sweet taste (Jin et al., 2006). Brazzein is widely recurited as sugar substitute in low caloric dietary formulas or for diabetes patients. Brazzein is a food additive for several years and no side effects have been reported (Yang & Lyu, 2008).
