Dicynthaurin: an antimicrobial peptide from hemocytes of the solitary tunicate, Halocynthia aurantium

We isolated a novel antimicrobial peptide, dicynthaurin, from hemocytes of a tunicate, Halocynthia aurantium. The native peptide had a mass of approxi mately 6.2 kDa and was composed of two 30-residue monomers without sequence homology to any previously identified peptides (ILQKAVLDCLKAAGSSLSKAAITAIY NKIT). Most cynthaurin molecules were C-terminally amidated and were linked covalently by a single cystine disulfide bond. When performed in membrane- mimetic environments, circular dichroism studies of dicynthaurin revealed l argely alpha -helical conformations. Dicynthaurin's broad-spectrum activity encompassed Gram-positive (Micrococcus luteus, Staphylococcus aureus, List eria monocytogenes) and Gram-negative bacteria (Escherichia coli, Pseudomon as aeruginosa), but not Candida albicans, a fungus. Although dicynthaurin w as purified from a marine invertebrate, its antimicrobial activity was opti mal at NaCl concentrations below 100 mM. This suggests that the antimicrobi al actions of this molecule may take place intracellularly (e.g., within a phagosome) rather than extracellularly. (C) 2001 Elsevier Science B.V. All rights reserved.