Esculentin-1c

Granular glands in the skins of frogs synthesize and secrete a remarkably diverse range of peptides capable of antimicrobial activity. These anuran skin antimicrobial peptides are commonly hydrophobic, cationic and form an amphipathic α-helix in a membrane mimetic solution. Recently, they have been considered as useful target molecules for developing new antibiotics drugs. Esculentin-1c is a 46-amino acid residue peptide isolated from skin secretions of the European frog, Rana esculenta. It displays the most potent antimicrobial activity among bioactive molecules. Esculentin-1c has the longest amino acids among all antimicrobial peptides. The present study solved the solution structure of esculentin-1c in TFE/water by NMR, for the first time. We conclude that this peptide is comprised of three α-helices with each helix showing amphipathic characteristics, which seems to be a key part for permeating into bacterial membranes, thus presenting antimicrobial activity.

The anuran (frogs and toads) skin is a rich source of antimicrobial peptides that can be developed therapeutically. We searched the skin secretions of Korean Rana esculenta for antimicrobial peptides, and isolated two cationic peptides with antimicrobial activity and little hemolytic activity: a 46-residue peptide of the esculentin-1 family and a 24-residue peptide of the brevinin-1 family. Their sequences showed some differences from the esculentins-1 and brevinins-1 of European Rana esculenta, indicating that sequence diversification of anuran skin antimicrobial peptides can arise from differences in habitat as well as from species differences. The 46-residue peptide named esculentin-1c had broad antimicrobial activity, while the 24-residue peptide named brevinin-1Ed exhibited limited activity. The solution structure of brevinin-1Ed was in good agreement with that of other brevinin-1-like peptides, with an amphipathic alpha-helix spanning residues 3-20, stabilized in membrane-mimetic environments. The weak bioactivity of brevinin-1Ed was attributable to the unusual presence of an anionic amino acid in the middle of the helical hydrophilic face. This report contributes to world-wide investigations of the structure-activity relationships and evolutional diversification of anuran-skin antimicrobial peptides.