Actinins as novel broad-spectrum AMP isolated from the tentacle of Anthozoan Actinia equina (Linnaeus, 1758)

Abstract

Capturing activities and defense mechanisms of Cnidarian are strongly associated with toxins and peptide with antimicrobial properties. AMP are an important component of many organisms’ innate immune system with a good inhibitory or killing effect against invaders pathogens. We investigated the AMP activity of acid extracts obtained from tentacle and body of Actinia equina (Cnidaria, Anthozoa) against Gram positive (Micrococcus lysodeikticus) and Gram negative (Escherichia coli, Vibrio alginolyticus) bacteria. The peptide fractions showed interesting minimum inhibitory concentrations (MIC) values (concentrations up to 0.125 μg/ml) against tested pathogens. Tentacle acid extracts exhibiting a good antimicrobial activity, were further investigated, characterized and the peptides purified by reverse phase chromatography on solid phase Sep-Pak C8 column followed by several HPLC runs on C18 column. A broad-spectrum antibacterial peptides activity was detected in 40 % acetonitrile fractions. The Peptide 6.2 has a molecular weight of 2612.91 Da and is composed of 27 amino acids (Actinin A); while peptide 7.3 has a molecular weight of 4323.07 Da and is composed of 35 amino acids (Actinin B). The two peptides were completely sequenced and their aa sequence revealed similarity with the already described AMPs identified in amphibians and fish, with anti-Gram+ & Gram-, antifungal, candidacidal, anti- Methicillin-resistant Staphylococcus aureus (MRSA) activity Actinins A and B were chemically synthesized and tested in vitro against the above-mentioned bacterial pathogens. The analysis identified the peptide Actinin B which showed an interesting antibacterial and can be considered good candidates for new therapeutic applications.