Structural studies on the antimicrobial peptide Brevinin 1E by spectroscopic methods

Skin extracts of frogs are a rich source of pharmacologically active peptides such as caeruleins, tachykinins, bradykinins, thyrotropin-releasing hormone, bombesin-like and opioid peptides. A large variety of antimicrobial peptides has been isolated from Rana species. These peptides, grouped in several families on the basis of differing length and distinct activity, were found to have one structural motif in common: an intramolecular disulfide bridge located at the C-terminal end, forming a seven-member ring, which was designated ‘Rana box’. Brevinin 1E is a 24-residue antimicrobial peptide isolated from the skin of a frog, Rana brevipoda. This peptide shows a broad range of antimicrobial activity against prokaryotic cells but shows very much hemolytic activity against human red blood cells. The solution structure of Brevinin 1E was studied by using CD (circular dichroism) and NMR (nuclear magnetic resonance) spectroscopy. CD investigation revealed that Brevinin 1E adopts random structure in aqueous solution but adopts mainly α-helical structure in TFE/water (6 : 4, v/v) solution. The three-dimensional structure of Brevinin 1E was determined in 60% TFE/water solution using homonuclear NMR spectroscopy. This peptide showed mainly an α-helical structure with amphipathic property. Its three-dimensional structure is similar to those of other peptides such as magainin, nigrocin and ranalexin. Therefore, Brevinin 1E can be classified into the family of antimicrobial peptides containing a single linear α-helix that interact with target microbial membrane, leading to cell death through disruption of membrane integrity.