1.A.70 The Molecule Against Microbes A (MamA) Family
A novel gene family coding for putative antimicrobial peptides was identified the sea squirt Ciona intestinalis, and one of these genes was molecularly cloned from the Northern European Ciona subspecies (Fedders et al., 2008). In situ hybridization and immunocytochemical analysis revealed that the natural peptide is synthesized and stored in a distinct haemocyte type, the univacuolar non-refractile granulocytes. Expression of the gene is up-regulated in haemocytes after immune challenge. The antimicrobial potency of the defense peptide was dependent on its cationic core region. The peptide was effective against Gram-negative and Gram-positive bacteria as well as the yeast, Candida albicans. The antibacterial activity of the peptide was retained at salt concentrations up to 450 mM NaCl. The peptide kills Gram-negative and Gram-positive bacteria by permeabilizing their cytoplasmic membranes. In the presence of liposomes composed of negatively charged phospholipids, the peptide adopts an alpha-helical structure. The peptide is non-cytolytic for mammalian erythrocytes.