**2.2 Antimicrobial peptides derived from chromogranin A**

Several new antimicrobial peptides isolated from the granules of chromaffin cells of the bovine adrenal medulla correspond to CGA-derived peptides (Figure 3). The corresponding sequences are highly conserved in human. Interestingly, the main cleavage site in position 78-79 of bCGA and the subsequent remove of the two basic residues K77 and K78 by the carboxipeptidase H (Metz-Boutigue et al., 1993) produces two antimicrobial fragments: vasostatin-I (VS-I; bCGA1-76) (Lugardon et al., 2000) and prochromacin (Prochrom; bCGA79-431) (Strub et al.,1996b). For these N- and C-terminal domains with antimicrobial activities several shorter active fragments were identified: for VS-I, bCGA1-40 (N CgA; NCA) (Shooshtarizadeh et al., 2010), bCGA47-66 (chromofungin; CHR) and for ProChrom, bCGA173-194 (Chromacin; Chrom) (Strub et al., 1996b) and bCGA344-364 (Catestatin; CAT) (Shooshtarizadeh et al., 2010). The unique disulfide bridge of bCGA is present in VS-I and NCA sequences. Two post-translational modifications are important for the expression of the antibacterial activity of Chrom: the phosphorylation of Y173 and the O-glycosylation of S186 [130] (Strub et al., 1996a). Furthermore, it is important to point out that a dimerization motif GXXXG similar to that reported for Glycophorin A (Brosig & Langosch, 1998) is present in the Chrom sequence (G184-G188).

#### **Vasostatin-I**

Vasostatin-I (VS-I) displays antimicrobial activity against (i) Gram-positive bacteria (*Micrococcus luteus* and *Bacillus megaterium*) with a minimal inhibitory concentration (MIC) in the range 0.1-1 µM; (ii) against filamentous fungi (*Neurospora crassa, Aspergillus fumigatus, Alternaria brassicola, Nectria haematococca, Fusarium culmorum, Fusarium oxysporum*) with a MIC of 0.5-3 µM and (iii) against yeast cells (*Saccharomyces cerevisiae, Candida albicans*) with a MIC of 2 µM (Lugardon et al., 2000). However VS-I is unable to inhibit the growth of *Escherichia coli* SBS363 and *Escherichia coli* D22. VS-I (Figure 3) possesses structural features specific for antimicrobial peptides, such as a global positive charge (+3), an equilibrated number of polar and hydrophobic residues (20:23) and the presence of a helical region CGA40-65 characterized to be a calmodulin-binding sequence (Lugardon et al., 2001; Yoo, 1992). The loss of the antibacterial activity of CGA7-57 suggests that the N- and C-terminal sequences are essential, nevertheless CGA7-57 is less efficient than VS-I against fungi. Besides, the disulfide bridge is essential for the antibacterial, but not the antifungal property. Altogether, these data suggest that antibacterial and antifungal activities of VS-I have different structural requirements (Lugardon et al., 2001). Interestingly, two helix-helix dimerization motifs important for the interaction with membranes such as LXXXXXXL, present in DAT and dopamine transporter sequences (Torres et al., 2003) are present in the bovine and human VS-I sequences (L42-L49; L57-L64).

Surface interaction of rhodamine-labelled bCGA1-40 was demonstrated using confocal microscopy after incubation of the labeled peptide with *Aspergillus fumigatus*, *Alternaria brassicola* and *Neurospora crassa* (Blois et al., 2006). In addition, the interaction of bCGA1-40 with monolayers of phospholipids and sterols, as models for the interaction with mammalian and fungal membranes was investigated by the surface tension technique (Blois et al., 2006; Maget-Dana et al., 1999). These studies demonstrated that the N-terminal bCGA1-40 fragment interacts with model membrane phospholipids in a manner consistent with an amphiphilic penetration into membranes in a concentration range relevant for biological activity in mammalian tissue (Blois et al., 2006).
