Short, multiple-stranded β-hairpin peptides have antimicrobial potency with high selectivity and salt resistance

The beta-hairpin structure has been proposed to exhibit potent antimicrobial properties with low cytotoxicity, thus, multiple beta-hairpin structures have been proved to be highly stable in structures containing tightly packed hydrophobic cores. The aim of this study was to develop peptide-based synthetic strategies for generating short, but effective AMPs as inexpensive antimicrobial agents. Multiple-stranded beta hairpin peptides with the same beta-hairpin unit, (WRXxRW)(n) where n = 1, 2, 3, or 4 and Xx represent the turn sequence, were synthesized, and their potential as antimicrobial agents was evaluated. Owning to the tightly packed hydrophobic core and paired Trp of this multiple-stranded beta-hairpin structure, all the 12-residues peptides exhibited high cell selectivity towards bacterial cells over human red blood cells (hRBCs), and the peptide W2 exhibited stronger antimicrobial activities with the MIC values of 2-8 mu M against various tested bacteria. Not only that, but W2 also showed obvious synergy with streptomycin and chloramphenicol against Escherichia coli, and displayed synergy with ciprofloxacin against Staphylococcus aureus with the FICI values <= 0.5. Fluorescence spectroscopy and electron microscopy analyses indicated that W2 kills microbial cells by permeabilizing the cell membrane and damaging membrane integrity. Collectively, based on the multiple beta-hairpin peptides, the ability to develop libraries of short and effective peptides will be a powerful approach to the discovery of novel antimicrobial agents. Statement of significance We successfully screened a peptide W2 ((WRPGRW)2) from a series of multiple-stranded beta-hairpin antimicrobial peptides based on the "S-shaped" motif that induced the formation of a globular structure, and Trp zipper was used to replace the disulfide bonds to reduce the cost of production. This novel structure applied to AMPs improved cell selectivity and salt stability. The findings of this study will promote the development of peptide-based antimicrobial biomaterials. Further exploration of these AMPs will allow for diverse biotechnological and clinical applications such as biomedical coating, food storaging, and animal feeding. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.