Pseudin-2: An Antimicrobial Peptide with Low Hemolytic Activity from the Skin of the Paradoxical Frog

Abstract

Four structurally related peptides (pseudins 1–4) with antimicrobial activity were isolated from an extract of the skin of the paradoxical frog Pseudis paradoxa (Pseudidae). Pseudin-2 (GLNALKKVFQGIHEAIKLINNHVQ) was the most abundant peptide (22 nmol/g tissue) and also the most potent (minimum inhibitory concentrations, MIC = 2.5 μM against Escherichia coli, 80 μM against Staphylococcus aureus, and 130 μM against Candida albicans). The concentration of pseudin-2 producing 50% hemolysis of human erythrocytes was >300 μM. Circular dichroism studies showed that the pseudins belong to the class of cationic, amphipathic α-helical antimicrobial peptides but their amino acid sequences are not similar to any previously characterized peptides from frog skin. The pseudins do, however, show sequence similarity with a region at the C-terminus of DEFT, a death effector domain-containing protein expressed in mammalian testicular germ cells that is involved in the regulation of apoptosis.