Isolation and characterization of pleurocidin, an antimicrobial peptide in the skin secretions of winter flounder.

Antimicrobial peptides are found in both myeloid cells and mucosal tissues of many vertebrates and invertebrates. These peptides are predicted to operate as a first-line host defense mechanism exerting broad-spectrum activity against pathogenic bacteria, fungi, parasites, and enveloped viruses. We report the characterization of a novel 25-residue linear antimicrobial peptide found in the skin mucous secretions of the winter flounder (Pleuronectes americanus). This peptide was purified through multiple chromatographic methods to obtain a single peak by reversed-phase high performance liquid chromatography. This purified peptide, which we named pleurocidin, exhibited antimicrobial activity against Escherichia coli in a bacterial cell lysis plate assay. Mass spectrometry and amino acid sequence analysis indicated that it is 25 amino acids in length. Pleurocidin is predicted to assume an amphipathic alpha-helical conformation similar to many other linear antimicrobial peptides. There is a high degree of homology between pleurocidin and two antimicrobial peptides, ceratotoxin from the Mediterranean fruit fly and dermaseptin from the skin of a hylid frog. The minimal inhibitory concentration and minimal bactericidal concentration of pleurocidin were determined against 11 different Gram-negative and Gram-positive bacteria. Immunohistochemistry locates pleurocidin in the epithelial mucous cells of flounder skin. Pleurocidin represents a novel antimicrobial peptide found in fish and may play a role in innate host defense.