Abstract
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 fromRanaspecies. 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 mainlyα-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 anα-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 linearα-helix that interact with target microbial membrane, leading to cell death through disruption of membrane integrity.
Highlights
The history of antimicrobial peptides runs in parallel with the penicillin work
Brevinin 1E has two conserved cysteines delineated by a disulfide bridge in the C-terminal region, which is characteristic of the antimicrobial peptides from Ranidae
Brevinin 1E has two proline residues, which are highly conserved in the antimicrobial peptides from Ranidae
Summary
The history of antimicrobial peptides runs in parallel with the penicillin work. It starts in 1939 with Dubos’ demonstration that ‘an unidentified soil bacillus’ produced some antimicrobial compounds that could prevent pneumococcal infections in mice. The solvent-filled unspecific pores, by permeating the membrane to various substances including ions, cause the electric potential to dissipate across the membrane, leading to death of the microbial cell These models explain the permeating effect of helical antimicrobial peptides, they do not account for their remarkable specificity of action, which may be partly explained by the difference in lipid composition of the membrane of the target cells and the exact nature of the peptide’s side chains. These antimicrobial peptides serve as immune substances and they are primary defense agents of innate immunity rather than secondary metabolites [23,40]. The solution structures of Brevinin 1E, a 24-residue antimicrobial peptide, were determined in 60% trifluoroethanol solution by using NMR to investigate the structure-activity relationship
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